{"title":"William Optics Imaging Accessories","description":"\u003cp\u003eWilliam Optics imaging accessories help with framing, focus and tilt in an astrophotography setup. Camera angle rotators in M54, M63 (for the 2.5\" focuser) and M92 versions let you turn the camera to frame a target without losing focus.\u003c\/p\u003e\u003cp\u003eBahtinov focusing masks come in sizes from 75-110mm up to 243-308mm, plus Bahtinov mask covers made for the GT81 and Z81, the GT71, Z73 and Star71II, and the Takahashi FSQ106. The image plane tilt adjuster corrects sensor tilt for even stars across the frame.\u003c\/p\u003e","products":[{"product_id":"william-optics-243-308mm-bahtinov-focusing-mask","title":"William Optics 243-308mm Bahtinov Focusing Mask","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eFits Dew Shields with Outer Diameters from 243mm to 308mm\u003c\/li\u003e\n\u003cli\u003eGenerates a Clear Three-Spike Diffraction Pattern for Precise Focusing\u003c\/li\u003e\n\u003cli\u003eEssential Tool for Deep-Sky and Planetary Astrophotography\u003c\/li\u003e\n\u003cli\u003eAdjustable Thumbscrews for a Secure Fit\u003c\/li\u003e\n\u003cli\u003eLightweight Design Minimizes Impact on Telescope Balance\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eWilliam Optics 243-308mm Bahtinov Focusing Mask\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Bahtinov Focusing Mask is the definitive tool for achieving critical focus, designed to fit telescopes with dew shield diameters from 243mm to 308mm. By generating an unmistakable diffraction pattern, this mask transforms the subjective act of focusing into a precise, repeatable, and rapid adjustment, ensuring your stellar images are perfectly sharp from the start.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eThe Bahtinov Pattern: Objective Focus in Seconds\u003c\/h3\u003e\n\u003cp\u003eA Bahtinov mask works by creating a set of three diffraction spikes around any bright star in your field of view. Two spikes form a fixed \"X,\" while a third central spike moves as you adjust your focuser. Perfect focus is achieved the moment this central spike is perfectly centered within the \"X\"—an unambiguous pattern that your eyes can verify instantly on a camera's live view screen.\u003c\/p\u003e\n\u003cp\u003eThis method removes all guesswork. It is faster and often more accurate than relying on visual estimation or chasing the smallest star size, giving you a physical, undeniable confirmation of critical focus every time you set up.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eAdjustable Fit for 243mm to 308mm Dew Shields\u003c\/h3\u003e\n\u003cp\u003eEngineered for versatility, this mask features adjustable mounting hardware to securely grip the outer wall of your telescope's dew shield. The 243mm to 308mm range makes it compatible with a wide array of popular instruments, including many 8\" to 11\" Schmidt-Cassegrains, larger refractors, and Newtonian reflectors.\u003c\/p\u003e\n\u003cp\u003eAttaching to the dew shield is a critical design choice. It prevents the mask from scratching your optical tube assembly and ensures a secure fit on tapered or unconventional tube designs, making it a universal solution for multiple telescopes in your collection.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eBahtinov Mask vs. FWHM Software: A Critical Advantage in Real-World Seeing\u003c\/h3\u003e\n\u003cp\u003eWhile software metrics like Full Width at Half Maximum (FWHM) are powerful, they are highly susceptible to atmospheric seeing. A moment of poor seeing can cause FWHM values to jump, leading you to settle on a focus position that isn't truly optimal. The Bahtinov pattern, however, is largely immune to this turbulence.\u003c\/p\u003e\n\u003cp\u003eThe diffraction spikes remain coherent and readable even when the star's image is boiling. This allows you to find the true point of best focus regardless of atmospheric conditions, a crucial advantage that saves time and prevents entire subframes from being compromised by soft stars.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I use the William Optics 243-308mm Bahtinov Mask?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eSimply place the mask over the end of your telescope's dew shield and secure it with the thumbscrews. Point your telescope at a moderately bright star, and engage your camera's live view. You will see a three-spike diffraction pattern. Adjust your focuser until the central spike is perfectly centered between the other two spikes. Once centered, your focus is perfect. Remove the mask before you begin imaging.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill this William Optics mask fit my Celestron 9.25\" SCT?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes, this mask is an excellent fit. A standard Celestron 9.25\" SCT dew shield has an outer diameter well within the 243mm to 308mm adjustment range of this mask, making it a perfect tool for achieving critical focus with that telescope.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs a Bahtinov mask better than my camera's live view zoom for focusing?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes, for astrophotography, a Bahtinov mask is significantly more precise. While zooming in helps you see the star, your eye can be tricked into accepting a \"good enough\" focus. The mask creates a pattern that shows you not just when you are in focus, but the \u003cstrong\u003edirection\u003c\/strong\u003e you need to move the focuser to achieve it, removing all ambiguity.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use the William Optics Bahtinov Mask for visual observing?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eA Bahtinov mask is a tool specifically for photographic focusing. While you could technically use it to focus an eyepiece, the diffraction pattern is faint and difficult to judge by eye. It is designed to be used with the high sensitivity and magnification of a camera's live view screen.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhy should I use this mask when imaging Jupiter?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eFor planetary imaging, critical focus is essential to resolve fine details like cloud bands on Jupiter or the Cassini Division in Saturn's rings. The best practice is to focus on a nearby bright star using the William Optics Bahtinov Mask, lock your focuser, and then slew back to the planet to begin your high-frame-rate capture. This ensures your focus is set with objective precision before you start recording.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eDoes the William Optics Bahtinov Mask work with color cameras?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eAbsolutely. The mask works perfectly with both monochrome and one-shot color cameras. The diffraction pattern is created by the physics of light and is independent of the type of sensor you are using. Some advanced users even use the slight color separation (chromatic aberration) at the tips of the spikes to fine-tune focus for different color channels.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eBrand\u003c\/td\u003e\n\u003ctd\u003eWilliam Optics\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eProduct Type\u003c\/td\u003e\n\u003ctd\u003eBahtinov Focusing Mask\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSKU\u003c\/td\u003e\n\u003ctd\u003eWO-BM-DS-GR150\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFitment\u003c\/td\u003e\n\u003ctd\u003eMounts on Telescope Dew Shield\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCompatible Dew Shield Diameter\u003c\/td\u003e\n\u003ctd\u003e243mm - 308mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eWilliam Optics 243-308mm Bahtinov Focusing Mask\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/william-optics-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eWilliam Optics 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":44967217004829,"sku":"WO-BM-DS-GR150","price":149.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/products\/William-Optics-243-308mm-Bahtinov-Focusing-Mask-BM-DS-GR150-1__38162.1596133226.1280.1280.jpg?v=1684339072"},{"product_id":"william-optics-75mm-110mm-bahtinov-focusing-mask","title":"William Optics 75mm -110mm Bahtinov Focusing Mask","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eFits Telescope Dew Shields from 75mm to 110mm\u003c\/li\u003e\n\u003cli\u003eCreates Sharp Diffraction Spikes for Precise Focusing\u003c\/li\u003e\n\u003cli\u003eIdeal for Small Apochromatic Refractors and Astrographs\u003c\/li\u003e\n\u003cli\u003eEliminates Subjective Focusing Errors\u003c\/li\u003e\n\u003cli\u003eA Critical Tool for Astrophotography\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eDownloads\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eWilliam Optics 75mm -110mm Bahtinov Focusing Mask\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Bahtinov Focusing Mask provides a simple, data-driven method for achieving perfect focus on any telescope with a dew shield outer diameter between 75mm and 110mm. This essential tool removes the guesswork from focusing, allowing you to achieve critically sharp stars for every astrophoto.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003ePrecision Focusing for Telescopes from 75mm to 110mm\u003c\/h3\u003e\n\u003cp\u003eThis mask operates on the principle of diffraction, splitting the light from a bright star into a distinct, symmetrical spike pattern. As you adjust your focuser, the central spike moves in or out; perfect focus is achieved the moment this spike is precisely centered between the outer two. The result is an unambiguous, repeatable focus point that is far more accurate than the human eye alone.\u003c\/p\u003e\n\u003cp\u003eDesigned for versatility, the mask is built to fit any telescope tube or dew shield with an outer diameter ranging from 75mm to 110mm. This makes it a perfect match for many popular wide-field refractors and other portable imaging instruments, ensuring your small-aperture setup can produce the sharpest possible images.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I use the William Optics 75-110mm Bahtinov Mask?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003ePlace the mask over the front of your telescope's dew shield or objective. Point to a moderately bright star, bring it into a rough focus, and view it on your camera's live-view screen. You will see a diffraction pattern of three spikes. Adjust the focuser until the central spike is perfectly centered between the other two, then lock your focuser and remove the mask.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill this William Optics mask fit my 80mm refractor?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes, most likely. This mask is designed for any telescope with an outer dew shield diameter between \u003cstrong\u003e75mm and 110mm\u003c\/strong\u003e. An 80mm refractor typically has a dew shield that falls comfortably within this range, making this mask an ideal fit.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use the 75-110mm Bahtinov mask for imaging Jupiter or the Moon?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo, a Bahtinov mask requires a point-like light source, such as a star, to generate its distinctive diffraction pattern. Planets like Jupiter or extended objects like the Moon do not produce the necessary pattern for the mask to work. For planets, it's best to focus on one of its moons first before turning to the planet itself.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat makes a Bahtinov mask more accurate than focusing by eye?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eFocusing by eye is subjective and can be affected by atmospheric seeing, eye fatigue, and small judgment errors. A Bahtinov mask converts the abstract concept of \"sharpness\" into a simple, symmetrical geometric pattern. Aligning the central spike is a precise, objective task that yields repeatable, perfect focus every time, independent of the observer.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the William Optics Bahtinov mask useful for visual observing?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eWhile primarily designed for the critical demands of astrophotography, a Bahtinov mask can also be used for visual observing to ensure your telescope is perfectly focused. However, its main benefit is for imaging, where even a tiny focusing error can ruin a long exposure.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhy does the diffraction pattern change as I focus?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe pattern is a direct visualization of the light cone from the star. When you are inside or outside of focus, the light cone is wider, causing the central diffraction spike to shift to one side. At the exact point of focus, the light cone is at its narrowest point, and the diffraction pattern becomes perfectly symmetrical.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eProduct Type\u003c\/td\u003e\n\u003ctd\u003eBahtinov Focusing Mask\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCompatible Dew Shield Diameter\u003c\/td\u003e\n\u003ctd\u003e75mm - 110mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/william-optics-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eWilliam Optics 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":44967217037597,"sku":"WO-BM-DS-GR45","price":81.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/products\/William-Optics-75mm-110mm-Bahtinov-Focusing-Mask-BM-DS-GR45-1__16153.1596133226.1280.1280.jpg?v=1684339076"},{"product_id":"william-optics-105-148mm-bahtinov-focusing-mask","title":"William Optics 105 -148mm Bahtinov Focusing Mask","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eFits Telescope Dew Shields from 105mm to 148mm\u003c\/li\u003e\n\u003cli\u003eGenerates Clear Diffraction Spikes for Focusing\u003c\/li\u003e\n\u003cli\u003eRemoves Subjectivity from Manual Focusing\u003c\/li\u003e\n\u003cli\u003eLightweight and Durable Construction\u003c\/li\u003e\n\u003cli\u003eIdeal for Astrophotography\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eWilliam Optics 105-148mm Bahtinov Focusing Mask\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Bahtinov Focusing Mask provides a fast, repeatable method for achieving critical focus for astrophotography. It is designed to fit any telescope with an outer dew shield diameter between 105mm and 148mm, making it a versatile tool for a wide range of optical tubes.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eUniversal Fit for Dew Shields from 105mm to 148mm\u003c\/h3\u003e\n\u003cp\u003eThis mask features adjustable mounting posts to securely grip the outer edge of your telescope's dew shield. This simple yet effective design allows it to fit a wide variety of instruments, from small refractors to mid-sized reflectors, as long as the dew shield diameter falls within the 105mm to 148mm range.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eAdjustable Fit:\u003c\/strong\u003e Securely mounts on any dew shield from 105mm to 148mm in diameter, ensuring broad compatibility.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eLightweight Construction:\u003c\/strong\u003e Adds minimal weight to the front of your telescope, preventing balance issues when imaging.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSimple Installation:\u003c\/strong\u003e Attaches and removes in seconds without any tools, letting you get to focusing quickly.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eThe Bahtinov Diffraction Pattern: Visualizing Perfect Focus\u003c\/h3\u003e\n\u003cp\u003eInstead of guessing when a star is at its smallest point, the Bahtinov mask creates a bright, easy-to-see diffraction pattern around it. As you adjust your focuser, you'll see a central diffraction spike move between two outer spikes. Perfect focus is achieved only when the central spike is perfectly centered and symmetrical.\u003c\/p\u003e\n\u003cp\u003eThis visual confirmation is immediate and unambiguous, even on a small camera screen. It works on any bright star and is significantly more accurate than relying on visual estimation, which can be affected by eye fatigue and atmospheric conditions.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eBahtinov Mask vs. FWHM: Why Visual Confirmation Matters\u003c\/h3\u003e\n\u003cp\u003eWhile autofocus routines using Full Width at Half Maximum (FWHM) are powerful, they can be misled by atmospheric turbulence (\"seeing\"), which causes star sizes to fluctuate moment by moment. A Bahtinov mask is largely immune to seeing; the diffraction pattern remains stable and readable even when the air is unsteady.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eSeeing Immunity:\u003c\/strong\u003e Provides a clear result even in turbulent atmospheric conditions that can fool software metrics.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNo Software Required:\u003c\/strong\u003e An essential analog tool that works directly at the eyepiece or on any live-view camera feed without needing a computer.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFaster Than Software:\u003c\/strong\u003e For manual focusing, finding the symmetrical spike pattern is often faster than waiting for software to analyze multiple exposures and calculate FWHM values.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I use the William Optics 105-148mm Bahtinov Mask?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eSimply place the mask over the front of your telescope's dew shield and point at a moderately bright star. Use your camera's live view, zoomed in on the star, to see the diffraction pattern. Adjust your focuser until the central spike is perfectly centered between the two outer spikes. Once centered, your focus is perfect, and you can remove the mask to begin imaging.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill this William Optics Bahtinov mask fit my telescope?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThis mask is designed to fit any telescope with an outer dew shield diameter that measures between \u003cstrong\u003e105mm and 148mm\u003c\/strong\u003e. Measure the outside diameter of your dew shield to confirm compatibility. The adjustable posts will securely hold it in place within this range.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat kind of star should I use to focus the William Optics Bahtinov Mask?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eChoose a bright star that is not overly brilliant, like Vega or Arcturus. An ideal star is bright enough to produce a clear diffraction pattern on your camera's live view but not so bright that it completely saturates the sensor, which can make the spikes difficult to judge. It's often best to choose a star near your imaging target to minimize focus shift from mirror flop or temperature changes.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use the William Optics 105-148mm Bahtinov Mask for visual observing?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eWhile designed for astrophotography, a Bahtinov mask can be used for visual focusing. However, the diffraction pattern is much easier to see and evaluate on a camera screen than through an eyepiece. For imaging, it is an essential tool; for visual, it can be helpful but is generally less necessary.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eI have a William Optics ZenithStar 81; will this 105-148mm mask fit?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes, this mask is a good fit for many popular refractors. To be certain, you should measure the outer diameter of your ZenithStar 81's dew shield. If it falls within the \u003cstrong\u003e105mm to 148mm\u003c\/strong\u003e range, the mask will fit perfectly.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the William Optics Bahtinov Mask help when imaging a target like the Orion Nebula (M42) with a DSLR?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eWhen imaging a faint object like the Orion Nebula (M42), achieving perfect focus is critical to capturing fine detail. Before you slew to the nebula, point your DSLR and telescope to a nearby bright star like Rigel. Use the Bahtinov mask with your camera's live view to set focus precisely. Then, remove the mask and move to M42, confident that your stars will be as sharp as possible in your final stacked image.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eMask Type\u003c\/td\u003e\n\u003ctd\u003eBahtinov\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFitment Method\u003c\/td\u003e\n\u003ctd\u003eMounts on Telescope Dew Shield\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFitment Diameter Range\u003c\/td\u003e\n\u003ctd\u003e105mm - 148mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eWilliam Optics 105-148mm Bahtinov Focusing Mask\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/william-optics-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eWilliam Optics 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":44967217103133,"sku":"WO-BM-DS-GR55","price":94.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/products\/William-Optics-105-148mm-Bahtinov-Focusing-Mask-BM-DS-GR55-1__76274.1596133226.1280.1280.jpg?v=1684339080"},{"product_id":"william-optics-172mm-235mm-bahtinov-focusing-mask","title":"William Optics 172mm -235mm Bahtinov Focusing Mask","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eFits Dew Shield Diameters from 172mm to 235mm\u003c\/li\u003e\n\u003cli\u003eGenerates Clear Diffraction Spikes for Precise Focusing\u003c\/li\u003e\n\u003cli\u003eIdeal for Astrophotography of Planets and Deep-Sky Objects\u003c\/li\u003e\n\u003cli\u003eAdjustable Mount for a Secure Fit on Multiple Telescopes\u003c\/li\u003e\n\u003cli\u003eLightweight and Durable Construction\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eDownloads\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eWilliam Optics 172mm - 235mm Bahtinov Focusing Mask\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Bahtinov Focusing Mask eliminates the guesswork of achieving critical focus by providing a simple, repeatable method for any telescope with a dew shield diameter from 172mm to 235mm. This essential tool is engineered for the astrophotographer who requires objective, perfect focus for every imaging session.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eOne Mask for Multiple Telescopes: 172mm to 235mm Fit\u003c\/h3\u003e\n\u003cp\u003eThis mask's key feature is its adjustable mounting system, designed to fit a wide range of instruments. The versatile 172mm to 235mm diameter range means a single mask can serve your entire collection of mid-sized telescopes, from 6-inch refractors to 8-inch SCTs, without needing to buy a custom-fit mask for each one. The secure mounting ensures it stays perfectly centered on your optical axis without slipping.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eFrom Guesswork to Certainty: Diffraction-Based Focusing\u003c\/h3\u003e\n\u003cp\u003eA Bahtinov mask creates a distinctive diffraction pattern of spikes around any bright star. As you adjust your focuser, a central spike moves in relation to two outer spikes. Perfect, critical focus is achieved only when the central spike is positioned exactly in the middle, creating a perfectly symmetrical pattern. This method is far more precise than relying on visual estimation or FWHM measurements, which can be easily skewed by atmospheric seeing conditions.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I use the William Optics 172-235mm Bahtinov Mask?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eUsing the \u003cstrong\u003eWilliam Optics Bahtinov Mask\u003c\/strong\u003e is straightforward. First, place the mask over the front of your telescope's dew shield and secure it. Point your telescope at a bright star, and bring it into rough focus. When you view the star through your camera's live view, you will see the diffraction spike pattern. Adjust your focuser until the central spike is perfectly centered between the two outer spikes. Once symmetrical, your focus is perfect, and you can remove the mask.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill the William Optics 172-235mm Bahtinov Mask fit my 8-inch SCT?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. An 8-inch (203mm) Schmidt-Cassegrain Telescope typically has a dew shield outer diameter that falls comfortably within the \u003cstrong\u003e172mm to 235mm\u003c\/strong\u003e range of this mask. This makes it an ideal focusing tool for popular 8\" SCT and EdgeHD models.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat makes this William Optics Bahtinov Mask better than just focusing by eye?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eFocusing by eye is subjective and can be affected by seeing conditions, eye fatigue, and the observer's visual acuity. The \u003cstrong\u003eWilliam Optics Bahtinov Mask\u003c\/strong\u003e removes this subjectivity by creating a clear, unmistakable pattern. Achieving a symmetrical diffraction pattern is an objective, repeatable indicator of perfect focus that does not depend on the observer's judgment.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use the William Optics Bahtinov Mask for planetary imaging of Jupiter?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eWhile you cannot focus on the planet itself, you can use the \u003cstrong\u003eWilliam Optics Bahtinov Mask\u003c\/strong\u003e on a nearby bright star to achieve perfect focus before slewing back to Jupiter. This ensures your telescope is critically focused for capturing fine details in Jupiter's cloud bands and the Great Red Spot. Once focused on the star, lock your focuser and remove the mask before beginning your planetary capture.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhich star is best for focusing with the William Optics Bahtinov Mask?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe ideal target is a moderately bright, isolated star. Stars like Vega, Arcturus, or Capella are excellent choices. Avoid using very dim stars, as the diffraction pattern will be faint, or extremely bright stars that might saturate your camera sensor, making the spikes difficult to judge accurately. Also, choose a star that is near the celestial object you plan to image to minimize focus shift from mirror flop or temperature changes.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eDoes the William Optics 172-235mm Bahtinov Mask work with autofocusers?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. Many automated focusing routines, such as those in N.I.N.A. or Sequence Generator Pro, can use a Bahtinov mask to assist in their focusing process. The software analyzes the diffraction pattern to determine the point of critical focus. The \u003cstrong\u003eWilliam Optics Bahtinov Mask\u003c\/strong\u003e provides a clear pattern that these programs can interpret effectively.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eSKU\u003c\/td\u003e\n\u003ctd\u003eWO-BM-DS-GR90\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFits Dew Shield Diameter\u003c\/td\u003e\n\u003ctd\u003e172mm - 235mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eWilliam Optics 172mm - 235mm Bahtinov Focusing Mask\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/william-optics-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eWilliam Optics 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":44967217201437,"sku":"WO-BM-DS-GR90","price":121.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/products\/William-Optics-172mm-235mm-Bahtinov-Focusing-Mask-BM-DS-GR90-1__73641.1596133227.1280.1280.jpg?v=1684339086"},{"product_id":"william-optics-bahtinov-mask-cover-for-gt71-z73-star71ii","title":"William Optics Bahtinov Mask Cover for GT71 \/ Z73 \/ Star71II","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003ePatented Bahtinov mask integrated into a dust cover\u003c\/li\u003e\n\u003cli\u003ePrecision-cut pattern for accurate focusing\u003c\/li\u003e\n\u003cli\u003eDesigned for William Optics GT71, Z73, and Star71II refractors\u003c\/li\u003e\n\u003cli\u003eDurable anodized aluminum construction\u003c\/li\u003e\n\u003cli\u003eAvailable in Gold, Red, and Blue finishes\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n  \u003cdiv class=\"DAV-bg-light\"\u003e\n    \u003cdiv class=\"DAV-section-center\"\u003e\n      \u003ch2\u003eWilliam Optics Bahtinov Mask Cover for GT71 \/ Z73 \/ Star71II\u003c\/h2\u003e\n      \u003cp\u003eEnsure every astrophoto taken with your William Optics GT71, Z73, or Star71II refractor starts with perfect focus. This patented Bahtinov Mask Cover replaces your standard dust cap, integrating a precision focusing tool directly into your telescope's protective cover. It’s the simplest, most effective way to achieve critical focus, ensuring you never waste valuable imaging time on soft stars again.\u003c\/p\u003e\n    \u003c\/div\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"DAV-bg-light\"\u003e\n    \u003cdiv class=\"DAV-section\"\u003e\n      \u003ch3\u003ePatented Dual-Function Design for GT71, Z73 \u0026amp; Star71II\u003c\/h3\u003e\n      \u003cp\u003eA Bahtinov mask is the most precise tool for achieving sharp focus for astrophotography. By placing this mask over your objective, a bright star displays a distinct three-spike diffraction pattern. Adjusting your focuser until the central spike is perfectly centered between the other two guarantees you’ve nailed critical focus, eliminating guesswork.\u003c\/p\u003e\n      \u003cp\u003eWilliam Optics' innovative design integrates this essential tool into the telescope's primary dust cap. This patented solution means your focusing mask is always with your telescope, preventing it from being forgotten or lost. Simply leave it on for protection, and you're ready to achieve perfect focus the moment you set up.\u003c\/p\u003e\n      \u003cul\u003e\n        \u003cli\u003e\n\u003cstrong\u003ePerfect Compatibility:\u003c\/strong\u003e Designed to fit the dew shields of the William Optics Gran Turismo 71, Zenithstar 73, and RedCat 71 (Star71II) refractors.\u003c\/li\u003e\n        \u003cli\u003e\n\u003cstrong\u003eAnodized Aluminum Construction:\u003c\/strong\u003e Machined from high-quality aluminum and anodized in your choice of Gold, Red, or Blue to match your William Optics hardware.\u003c\/li\u003e\n        \u003cli\u003e\n\u003cstrong\u003eInstant Focus Confirmation:\u003c\/strong\u003e Provides clear, unambiguous visual feedback for achieving perfect focus through your camera's live view screen.\u003c\/li\u003e\n      \u003c\/ul\u003e\n    \u003c\/div\u003e\n  \u003c\/div\u003e\n\n\u003c\/div\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I use the William Optics Bahtinov Mask Cover to focus my GT71 on a star like Vega?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eSimply place the Bahtinov Mask Cover over the end of your GT71's dew shield, point the telescope at a bright star like Vega (Alpha Lyrae), and view the star on your camera's live view screen. You will see a pattern of three diffraction spikes. Adjust your focuser until the central spike is perfectly symmetrical and centered between the two outer spikes. Once centered, your focus is perfect.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eWill this mask help me achieve sharp focus for nebula imaging with my Z73 refractor?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eAbsolutely. For nebula imaging, achieving critical focus on the surrounding stars is essential. Before you slew to your target nebula, use the William Optics Bahtinov Mask Cover on a nearby bright star to set your focus. This ensures your stars are as tight as possible, resulting in a much sharper final image of the nebula.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eWhat is the main advantage of having the Bahtinov mask built into the lens cover?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eThe primary advantage is convenience and availability. A separate Bahtinov mask can be easily forgotten, misplaced, or damaged. By integrating it into the dust cover, William Optics ensures this critical focusing tool is always with your telescope, protected and ready for use whenever you are.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eIs the William Optics Bahtinov Mask Cover compatible with any other telescopes?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eNo, this model is specifically designed for the dew shield diameters of the \u003cstrong\u003eWilliam Optics GT71\u003c\/strong\u003e, \u003cstrong\u003eZ73\u003c\/strong\u003e, and \u003cstrong\u003eStar71II\u003c\/strong\u003e refractors. It will not provide a secure fit or proper function on other telescopes.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eWhat am I looking for in the diffraction pattern when using this Bahtinov mask?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eYou are looking for perfect symmetry. When out of focus, the central diffraction spike will be shifted to one side of the \"X\" pattern. As you adjust the focuser, this central spike moves. Perfect focus is achieved at the exact point where the central spike is positioned perfectly in the middle of the \"X,\" creating a star-like, six-pointed pattern.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eDoes the color of the William Optics Bahtinov Mask Cover affect its performance?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eNo, the color (Gold, Red, or Blue) is purely cosmetic. The anodized finish is designed to match the aesthetic of William Optics telescopes and accessories. The performance of the Bahtinov mask pattern is identical across all color options.\u003c\/p\u003e\n  \u003c\/div\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n  \u003ctable class=\"DAV-specifications\"\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n\u003ctd\u003eCompatibility\u003c\/td\u003e\n\u003ctd\u003eWilliam Optics GT71, Z73, Star71II\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eFunction\u003c\/td\u003e\n\u003ctd\u003eFocusing Mask and Dust Cover\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eMaterial\u003c\/td\u003e\n\u003ctd\u003eAnodized Aluminum\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eAvailable Options\u003c\/td\u003e\n\u003ctd\u003eGold, Blue, Red\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n  \u003cul class=\"DAV-grid\"\u003e\n    \u003cli class=\"DAV-grid-item\"\u003e\n      \u003cdiv\u003e\n        \u003cp class=\"DAV-item-title\"\u003eWilliam Optics Bahtinov Mask Cover\u003c\/p\u003e\n        \u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n      \u003c\/div\u003e\n    \u003c\/li\u003e\n  \u003c\/ul\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/william-optics-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eWilliam Optics 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Gold","offer_id":44967218315549,"sku":"WO-CPBM-71GD","price":163.0,"currency_code":"CAD","in_stock":true},{"title":"Blue","offer_id":44967218348317,"sku":"WO-CPBM-71BU","price":147.0,"currency_code":"CAD","in_stock":true},{"title":"Red","offer_id":44967218381085,"sku":"WO-CPBM-71RD","price":163.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/products\/William-Optics-Bahtinov-Mask-Cover-for-WO-70-Series-Telescopes-CPBM-71-1__68564.1596133230.1280.1280.jpg?v=1684339261"},{"product_id":"william-optics-bahtinov-mask-cover-for-gt81-z81","title":"William Optics Bahtinov Mask Cover for GT81 \/ Z81","description":"\u003cul\u003e\n\t\u003cli\u003eBahtinov mask cover for William Optics GT81 and Z81 telescopes\u003c\/li\u003e\n\t\u003cli\u003eEnhances focusing accuracy for astrophotography\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\t\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cul class=\"tabs-content\"\u003e\n\t\u003cli class=\"active\"\u003e\n\t\t\u003cp\u003e\nThe William Optics Bahtinov Mask Cover is an essential accessory for precise focusing in astrophotography. Designed to fit the William Optics GT81 and Z81 telescopes, this Bahtinov mask cover ensures accurate focus for your celestial observations and imaging.\n\t\t\u003c\/p\u003e\n\t\t\u003cdiv class=\"warning\"\u003e\n\t\t\t\u003cimg alt=\"Disclaimer\" src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/warning-logo.svg?v=1714663206\" width=\"25px\"\u003e\n\t\t\t\u003cp\u003e\nSpecifically designed for the William Optics GT81 and Z81 telescopes.\n\t\t\t\u003c\/p\u003e\n\t\t\u003c\/div\u003e\n\t\t\n\t\t\u003cdiv\u003e\n\t\t\t\u003ch3\u003eCompatibility\u003c\/h3\u003e\n\t\t\t\u003chr\u003e\n\t\t\t\u003cdiv class=\"two-columns-section\"\u003e\n\t\t\t\t\u003cdiv class=\"text-side-2\"\u003e\n\t\t\t\t\t\u003cp\u003e\nThe Bahtinov mask cover is custom-made to fit William Optics GT81 and Z81 telescopes, ensuring a secure fit and optimal performance.\n\t\t\t\t\t\u003c\/p\u003e\n\t\t\t\t\u003c\/div\u003e\n\t\t\t\t\u003cdiv class=\"image-side-2\" data-mce-style=\"text-align: start;\" style=\"text-align: start;\"\u003e\n\t\t\t\t\t\u003cimg alt=\"William Optics Bahtinov Mask Cover for GT81 \/ Z81\" src=\"https:\/\/davidastro.com\/cdn\/shop\/products\/William-Optics-Bahtinov-Mask-Cover-for-WO-81-Series-Telescopes-CPBM-81-1__39346.1596133231.1280.1280_832x832.jpg?v=1684339269\" style=\"margin-bottom: 16px; float: none;\"\u003e\n\t\t\t\t\u003c\/div\u003e\n\t\t\t\u003c\/div\u003e\n\n\t\t\t\u003cdiv data-mce-style=\"backgroundcolor: #0a0001; border-radius: 5px;\" style=\"background-color: #0a0001; border-radius: 5px;\"\u003e\n\t\t\t\t\u003ch3 style=\"color: white!important;\"\u003eEnhanced Focusing Accuracy\u003c\/h3\u003e\n\t\t\t\t\u003chr\u003e\n\t\t\t\t\u003cdiv class=\"two-columns-section\"\u003e\n\t\t\t\t\t\u003cdiv class=\"image-side-2\" data-mce-style=\"text-align: start;\" style=\"text-align: start;\"\u003e\n\t\t\t\t\t\t\u003cimg alt=\"William Optics Bahtinov Mask Cover for GT81 \/ Z81\" src=\"https:\/\/davidastro.com\/cdn\/shop\/products\/William-Optics-Bahtinov-Mask-Cover-for-WO-81-Series-Telescopes-CPBM-81-2__20318.1596133231.1280.1280_832x832.jpg?v=1684339269\" style=\"margin-bottom: 16px; float: none;\"\u003e\n\t\t\t\t\t\u003c\/div\u003e\n\t\t\t\t\t\u003cdiv class=\"text-side-2\"\u003e\n\t\t\t\t\t\t\u003cp style=\"color: white!important;\"\u003e\nThe Bahtinov mask pattern allows for precise focusing by creating diffraction spikes when viewing a bright star, making it easy to achieve perfect focus for astrophotography.\n\t\t\t\t\t\t\u003c\/p\u003e\n\t\t\t\t\t\u003c\/div\u003e\n\t\t\t\t\u003c\/div\u003e\n\t\t\t\u003c\/div\u003e\n\t\t\u003c\/div\u003e\n\n\t\t\u003ch3\u003eDurable Construction\u003c\/h3\u003e\n\t\t\u003chr\u003e\n\t\t\u003cp\u003e\nMade from high-quality materials, the Bahtinov mask cover is built to withstand regular use and provides long-lasting durability.\n\t\t\u003c\/p\u003e\n\t\t\n\t\t\u003ch3\u003ePrecision Engineering\u003c\/h3\u003e\n\t\t\u003chr\u003e\n\t\t\u003cp\u003e\nEngineered for a perfect fit on the GT81 and Z81 telescopes, the Bahtinov mask cover ensures stability and accuracy during focusing.\n\t\t\u003c\/p\u003e\n\n\t\t\u003ch3\u003eEase of Use\u003c\/h3\u003e\n\t\t\u003chr\u003e\n\t\t\u003cp\u003e\nThe Bahtinov mask cover is easy to attach and remove, making it convenient for quick adjustments in the field.\n\t\t\u003c\/p\u003e\n\n\t\t\u003ch3\u003eVersatility\u003c\/h3\u003e\n\t\t\u003chr\u003e\n\t\t\u003cp\u003e\nIdeal for both beginner and experienced astrophotographers, the Bahtinov mask cover is an essential tool for achieving sharp, detailed images of celestial objects.\n\t\t\u003c\/p\u003e\n\t\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Gold","offer_id":44967218446621,"sku":"WO-CPBM-81GD","price":163.0,"currency_code":"CAD","in_stock":true},{"title":"Blue","offer_id":44967218479389,"sku":"WO-CPBM-81BU","price":163.0,"currency_code":"CAD","in_stock":true},{"title":"Red","offer_id":44967218512157,"sku":"WO-CPBM-81RD","price":163.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/products\/William-Optics-Bahtinov-Mask-Cover-for-WO-81-Series-Telescopes-CPBM-81-1__39346.1596133231.1280.1280.jpg?v=1684339269"},{"product_id":"william-optics-bahtinov-mask-cover-for-takahashi-fsq106","title":"William Optics Bahtinov Mask Cover for Takahashi FSQ106","description":"\u003cul\u003e\n\t\u003cli\u003eBahtinov mask cover for Takahashi FSQ106 telescope\u003c\/li\u003e\n\t\u003cli\u003eEnhances focusing accuracy for astrophotography\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\t\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cul class=\"tabs-content\"\u003e\n\t\u003cli class=\"active\"\u003e\n\t\t\u003cp\u003e\nThe William Optics Bahtinov Mask Cover is an essential accessory for precise focusing in astrophotography. Designed to fit the Takahashi FSQ106 telescope, this Bahtinov mask cover ensures accurate focus for your celestial observations and imaging.\n\t\t\u003c\/p\u003e\n\t\t\u003cdiv class=\"warning\"\u003e\n\t\t\t\u003cimg alt=\"Disclaimer\" src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/warning-logo.svg?v=1714663206\" width=\"25px\"\u003e\n\t\t\t\u003cp\u003e\nSpecifically designed for the Takahashi FSQ106 telescope.\n\t\t\t\u003c\/p\u003e\n\t\t\u003c\/div\u003e\n\t\t\n\t\t\u003cdiv\u003e\n\t\t\t\u003ch3\u003eCompatibility\u003c\/h3\u003e\n\t\t\t\u003chr\u003e\n\t\t\t\u003cdiv class=\"two-columns-section\"\u003e\n\t\t\t\t\u003cdiv class=\"text-side-2\"\u003e\n\t\t\t\t\t\u003cp\u003e\nThe Bahtinov mask cover is custom-made to fit the Takahashi FSQ106 telescope, ensuring a secure fit and optimal performance.\n\t\t\t\t\t\u003c\/p\u003e\n\t\t\t\t\u003c\/div\u003e\n\t\t\t\t\u003cdiv class=\"image-side-2\" data-mce-style=\"text-align: start;\" style=\"text-align: start;\"\u003e\n\t\t\t\t\t\u003cimg alt=\"William Optics Bahtinov Mask Cover for Takahashi FSQ106\" src=\"https:\/\/davidastro.com\/cdn\/shop\/products\/William-Optics-Bahtinov-Mask-Cover-for-Takahashi-FSQ106-CPBM-TH106-1__35534.1596133232.1280.1280_832x832.jpg?v=1684339107\" style=\"margin-bottom: 16px; float: none;\"\u003e\n\t\t\t\t\u003c\/div\u003e\n\t\t\t\u003c\/div\u003e\n\n\t\t\t\u003cdiv data-mce-style=\"backgroundcolor: #0a0001; border-radius: 5px;\" style=\"background-color: #0a0001; border-radius: 5px;\"\u003e\n\t\t\t\t\u003ch3 style=\"color: white!important;\"\u003eEnhanced Focusing Accuracy\u003c\/h3\u003e\n\t\t\t\t\u003chr\u003e\n\t\t\t\t\u003cdiv class=\"two-columns-section\"\u003e\n\t\t\t\t\t\u003cdiv class=\"image-side-2\" data-mce-style=\"text-align: start;\" style=\"text-align: start;\"\u003e\n\t\t\t\t\t\t\u003cimg alt=\"William Optics Bahtinov Mask Cover for Takahashi FSQ106\" src=\"https:\/\/davidastro.com\/cdn\/shop\/products\/William-Optics-Bahtinov-Mask-Cover-for-Takahashi-FSQ106-CPBM-TH106-2__47935.1596133232.1280.1280_832x832.jpg?v=1684339107\" style=\"margin-bottom: 16px; float: none;\"\u003e\n\t\t\t\t\t\u003c\/div\u003e\n\t\t\t\t\t\u003cdiv class=\"text-side-2\"\u003e\n\t\t\t\t\t\t\u003cp style=\"color: white!important;\"\u003e\nThe Bahtinov mask pattern allows for precise focusing by creating diffraction spikes when viewing a bright star, making it easy to achieve perfect focus for astrophotography.\n\t\t\t\t\t\t\u003c\/p\u003e\n\t\t\t\t\t\u003c\/div\u003e\n\t\t\t\t\u003c\/div\u003e\n\t\t\t\u003c\/div\u003e\n\t\t\u003c\/div\u003e\n\n\t\t\u003ch3\u003eDurable Construction\u003c\/h3\u003e\n\t\t\u003chr\u003e\n\t\t\u003cp\u003e\nMade from high-quality materials, the Bahtinov mask cover is built to withstand regular use and provides long-lasting durability.\n\t\t\u003c\/p\u003e\n\t\t\n\t\t\u003ch3\u003ePrecision Engineering\u003c\/h3\u003e\n\t\t\u003chr\u003e\n\t\t\u003cp\u003e\nEngineered for a perfect fit on the Takahashi FSQ106 telescope, the Bahtinov mask cover ensures stability and accuracy during focusing.\n\t\t\u003c\/p\u003e\n\n\t\t\u003ch3\u003eEase of Use\u003c\/h3\u003e\n\t\t\u003chr\u003e\n\t\t\u003cp\u003e\nThe Bahtinov mask cover is easy to attach and remove, making it convenient for quick adjustments in the field.\n\t\t\u003c\/p\u003e\n\n\t\t\u003ch3\u003eVersatility\u003c\/h3\u003e\n\t\t\u003chr\u003e\n\t\t\u003cp\u003e\nIdeal for both beginner and experienced astrophotographers, the Bahtinov mask cover is an essential tool for achieving sharp, detailed images of celestial objects.\n\t\t\u003c\/p\u003e\n\t\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Blue","offer_id":44967218708765,"sku":"WO-CPBM-TH106BS","price":266.0,"currency_code":"CAD","in_stock":true},{"title":"Red","offer_id":44967218741533,"sku":"WO-CPBM-TH106RS","price":266.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/products\/William-Optics-Bahtinov-Mask-Cover-for-Takahashi-FSQ106-CPBM-TH106-1__35534.1596133232.1280.1280.jpg?v=1684339107"},{"product_id":"william-optics-image-plane-tilt-adjuster","title":"William Optics Image Plane Tilt Adjuster","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eDesigned exclusively for the William Optics RedCat 51 astrograph\u003c\/li\u003e\n\u003cli\u003eCorrects image plane tilt for perfectly round stars across the frame\u003c\/li\u003e\n\u003cli\u003eAdds only 12.2 mm of optical path length\u003c\/li\u003e\n\u003cli\u003eConnects via M56 female thread to the telescope\u003c\/li\u003e\n\u003cli\u003eProvides a standard M54 male thread for your camera or filter wheel\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eWilliam Optics Image Plane Tilt Adjuster for RedCat 51\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Image Plane Tilt Adjuster is an essential upgrade for imagers using the RedCat 51, adding only 12.2 mm of optical length to the imaging train. It connects directly to the telescope's native M56 thread and provides a standard M54 output for your camera, enabling precise, independent adjustment to eliminate sensor tilt and achieve a perfectly flat field.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eAchieve a Perfectly Flat Field: The 12.2mm RedCat 51 Tilt Adjuster\u003c\/h3\u003e\n\u003cp\u003eThe fast optical system of the RedCat 51 is extremely sensitive to sensor tilt, where even a few microns of misalignment can result in elongated stars in the corners of an otherwise sharp image. This tilt adjuster provides the fine control needed to make the camera sensor perfectly orthogonal to the telescope's optical axis, ensuring the RedCat's flat-field correction is fully realized from edge to edge.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eSeamless Integration with M56 and M54 Threads\u003c\/h3\u003e\n\u003cp\u003eEngineered as a drop-in solution, this adjuster features an M56 female thread on the light-in side that attaches directly to the RedCat 51's focuser drawtube. The light-out side provides a male M54 thread, a common standard for connecting to most filter wheels, off-axis guiders, and dedicated astronomy cameras. This robust, threaded connection maintains rigidity while allowing for the necessary micro-adjustments to perfect your images.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat is the primary purpose of the William Optics Tilt Adjuster for the RedCat 51?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eIts purpose is to correct for sensor tilt. This is a slight misalignment between your camera's sensor and the telescope's focal plane, which can cause stars to be sharp in the center of your image but elongated or out-of-focus in the corners. This device allows you to make fine adjustments to align the sensor perfectly, ensuring sharp stars across the entire field of view.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I know if I need this tilt adjuster for my RedCat 51?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eIf you notice that stars in the corners of your images are not perfectly round while the stars in the center are, you likely have sensor tilt. The effect is most noticeable with large sensors and the fast optics of the RedCat 51. This adjuster is the definitive solution to that problem.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill this WO-M-FD-RC51 tilt adjuster work with other telescopes?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo, this adjuster is designed specifically as an upgrade for the William Optics RedCat 51 astrograph. Its threading (M56) and optical length (12.2 mm) are engineered to integrate seamlessly into that specific optical train.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the 12.2 mm optical length of this tilt adjuster affect my imaging train?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe 12.2 mm of length it adds must be factored into your total back focus distance. You will need to reduce the length of your other extension tubes by 12.2 mm to ensure your camera sensor remains at the correct distance from the RedCat 51's final lens element.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat are the input and output threads on the William Optics Tilt Adjuster?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe adjuster has the following connections:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eTelescope Side (Light-In):\u003c\/strong\u003e M56 x 0.75 female thread\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCamera Side (Light-Out):\u003c\/strong\u003e M54 x 0.75 male thread\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIf I'm imaging the Andromeda Galaxy (M31) with my RedCat 51 and a full-frame sensor, why is this adjuster critical?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eImaging a large target like the Andromeda Galaxy (M31) with a full-frame sensor pushes the RedCat 51's image circle to its limits. Any minor sensor tilt will be immediately obvious as misshapen stars in the corners of your frame, ruining the large, flat field you're trying to capture. This tilt adjuster is critical for ensuring that the thousands of stars across M31's spiral arms are rendered as perfect pinpoints.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eCompatibility\u003c\/td\u003e\n\u003ctd\u003eWilliam Optics RedCat 51\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTelescope Connection (Light-In)\u003c\/td\u003e\n\u003ctd\u003eM56 x 0.75 Female Thread\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCamera Connection (Light-Out)\u003c\/td\u003e\n\u003ctd\u003eM54 x 0.75 Male Thread\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOptical Length\u003c\/td\u003e\n\u003ctd\u003e12.2 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eWilliam Optics Image Plane Tilt Adjuster\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/william-optics-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eWilliam Optics 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":44967237681437,"sku":"WO-M-FD-RC51","price":83.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/products\/William-Optics-Image-Plane-Tilt-Adjuster-M-FD-RC51-1__19291.1596133294.1280.1280.jpg?v=1684339589"},{"product_id":"william-optics-camera-angle-rotator-for-2-5-m63-focuser","title":"William Optics Camera Angle Rotator for 2.5\" M63 Focuser","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eAdds 360° of smooth camera rotation\u003c\/li\u003e\n\u003cli\u003eDesigned for William Optics 2.5\" focusers\u003c\/li\u003e\n\u003cli\u003eSecure M63 male and female threads\u003c\/li\u003e\n\u003cli\u003eMaintains optical alignment during adjustment\u003c\/li\u003e\n\u003cli\u003eLow-profile design minimizes back focus usage\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eWilliam Optics Camera Angle Rotator for 2.5\" M63 Focuser\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Camera Angle Rotator provides 360° of precise framing adjustment for imagers using the William Optics 2.5\" focuser with an M63 thread connection. This essential accessory allows you to perfectly compose your astrophotography targets without ever needing to unthread your camera or disrupt your optical train's alignment.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003e360° Framing Rotation for 2.5\" M63 Focusers\u003c\/h3\u003e\n\u003cp\u003eThis rotator threads directly onto the M63 drawtube of your William Optics 2.5\" focuser, providing a secure, non-flexing connection for your camera and accessories. A simple twist of the rotator housing allows for smooth, continuous rotation, letting you dial in the perfect orientation for targets like the Andromeda Galaxy (M31) or capture the full extent of the Veil Nebula complex. Once framed, the rotator locks firmly in place, preserving the rigid connection required for sharp, long-exposure images.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat is the main purpose of the William Optics M63 Camera Angle Rotator?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eIts primary purpose is to allow you to rotate your imaging camera to achieve the best possible composition for an astronomical target. The \u003cstrong\u003eWilliam Optics M63 Camera Angle Rotator\u003c\/strong\u003e lets you do this without loosening the camera from the focuser, which prevents potential sensor tilt and maintains a solid imaging train.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the WO-M-CAA63 help when imaging large targets like the Andromeda Galaxy (M31)?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eFor large, elongated targets like the Andromeda Galaxy (M31) or the Pleiades (M45), fitting the object into your camera's field of view is critical. This rotator lets you orient your rectangular sensor to match the target's longest axis, ensuring you capture the entire object and its faint outer extensions in a single, well-composed frame.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use this M63 rotator to frame intricate targets like the Horsehead Nebula (B33)?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. For targets with specific aesthetic orientations, like positioning the Horsehead Nebula (B33) relative to the Flame Nebula (NGC 2024), precise framing is key. The \u003cstrong\u003eWO-M-CAA63 rotator\u003c\/strong\u003e gives you fine control to compose the shot exactly as you envision it, turning a simple snapshot into a carefully crafted astrophoto.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill this rotator work with focusers other than a William Optics 2.5\" M63 model?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo, this rotator is specifically designed with \u003cstrong\u003eM63 threads\u003c\/strong\u003e to match the drawtube of William Optics 2.5\" focusers. It is not compatible with focusers that use different thread sizes or connection types.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I lock the William Optics rotator in place once I have my desired angle?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eMost camera angle rotators, including this William Optics model, feature a thumbscrew or a locking collar. Once you have rotated the camera to the desired position, you simply tighten the lock to prevent any further movement during your imaging session, ensuring stability.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill the WO-M-CAA63 introduce flexure into my imaging train?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe William Optics rotator is engineered to provide a rigid connection. When properly tightened and used within the focuser's load capacity, it should not introduce any noticeable flexure. It is designed to maintain the mechanical integrity of your optical path from the focuser to the camera sensor.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eProduct Name\u003c\/td\u003e\n\u003ctd\u003eWilliam Optics Camera Angle Rotator for 2.5\" M63 Focuser\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eThread Type\u003c\/td\u003e\n\u003ctd\u003eM63\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCompatible Focuser\u003c\/td\u003e\n\u003ctd\u003eWilliam Optics 2.5\" Focuser\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/william-optics-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eWilliam Optics 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":44967238566173,"sku":"WO-M-CAA63","price":178.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/products\/William-Optics-Camera-Angle-Rotator-for-2-5-inch-M63-Focuser-M-CAA63-1__74749.1596133305.1280.1280.jpg?v=1684339605"},{"product_id":"william-optics-m-caa54","title":"William Optics M54 Camera Angle Rotator (CAA)","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003e360° of precise framing rotation\u003c\/li\u003e\n\u003cli\u003eStandard M54 male and female threads\u003c\/li\u003e\n\u003cli\u003eAdds a minimal 30.2 mm to the optical path\u003c\/li\u003e\n\u003cli\u003eSecurely locks orientation for long exposures\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eWilliam Optics M54 Camera Angle Rotator (CAA)\u003c\/h2\u003e\n\u003cp\u003eThe William Optics M54 Camera Angle Rotator (CAA) provides 360° of precise framing adjustment for your imaging train, inserting between your flattener and camera while adding only 30.2 mm to your optical path. This essential accessory allows you to perfectly compose targets like elongated galaxies or sprawling nebulae without loosening your camera or disrupting your optical alignment.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003e360° Framing with a 30.2mm Optical Path\u003c\/h3\u003e\n\u003cp\u003eAchieving the perfect image orientation is critical, and the WO M54 CAA makes it simple. A smooth rotational mechanism allows for fine, controlled adjustments to match your camera sensor to the dimensions of your target. The rotator's key design consideration is its 30.2 mm optical length, a fixed value that must be factored into your back focus calculations to ensure a flat field.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eM54 Thread Standard:\u003c\/strong\u003e Features M54x0.75 male and female threads, ensuring compatibility with a wide ecosystem of William Optics flatteners, reducers, and many third-party cameras and accessories.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrecise Back Focus Integration:\u003c\/strong\u003e The 30.2 mm thickness is a known constant, allowing you to accurately subtract it from your required back focus distance and fill the remaining gap with standard M54 spacers.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eLocking Mechanism:\u003c\/strong\u003e Once you've set your desired frame, a secure locking screw holds the rotator firmly in place, preventing any drift during a long imaging session.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I install the William Optics M54 CAA in my imaging train?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe WO M54 CAA is designed to be threaded between two M54-compatible components. Typically, you would thread it directly onto the M54 output of your field flattener or reducer, and then attach your M54 spacers and camera to the female side of the rotator.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eDoes the 30.2 mm optical length of the WO M54 Rotator affect my back focus?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes, absolutely. The \u003cstrong\u003e30.2 mm optical length\u003c\/strong\u003e is a critical measurement that consumes part of your total back focus distance. If your flattener requires 55 mm of back focus, installing the rotator means you will need an additional 24.8 mm of spacers (55 - 30.2 = 24.8) between the rotator and your camera sensor to achieve a perfectly flat field.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the William Optics M54 CAA compatible with non-William Optics telescopes?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. As long as your telescope's flattener, reducer, or camera system uses the standard \u003cstrong\u003eM54x0.75 thread\u003c\/strong\u003e, the William Optics CAA will be compatible. It is not proprietary to William Optics telescopes.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhen would I use the WO M54 Camera Angle Rotator for imaging the Andromeda Galaxy (M31)?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe Andromeda Galaxy (M31) is a very wide, elliptical target. To fit its full span onto a rectangular camera sensor, you often need to orient the long axis of your sensor with the long axis of the galaxy. The WO M54 CAA allows you to make this fine rotational adjustment to perfectly frame M31 without rotating your entire, heavier imaging train.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use the WO M54 CAA with a filter wheel and off-axis guider?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. The rotator is typically placed first in the imaging train after the flattener. This allows you to rotate the entire subsequent assembly—including the off-axis guider, filter wheel, and camera—as a single locked unit. This ensures your guide camera maintains its orientation relative to the main imaging camera.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the WO M54 CAA lock its position once I have the correct framing?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe William Optics M54 CAA features a knurled thumbscrew on its side. Once you have rotated your camera to the desired angle, you simply tighten this screw. This applies pressure and securely locks the rotational position, preventing any unwanted movement during your exposure sequence.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eInput Connection\u003c\/td\u003e\n\u003ctd\u003eM54 (male)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOutput Connection\u003c\/td\u003e\n\u003ctd\u003eM54 (female)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOptical Path Length\u003c\/td\u003e\n\u003ctd\u003e30.2 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eWilliam Optics M54 Camera Angle Rotator\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/william-optics-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eWilliam Optics 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":52853691515165,"sku":"WO-M-CAA54","price":164.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/WilliamOptics-WO-Camera-Angle-Rotator-CAA-1_efbd93d4-61ab-4595-97c1-598bafd288c7.jpg?v=1788457860"}],"url":"https:\/\/davidastro.com\/collections\/william-optics-imaging-accessories.oembed","provider":"David Astro","version":"1.0","type":"link"}