{"product_id":"svbony-sv238-off-axis-guider-oag","title":"SVBONY SV238 Off-Axis Guider (OAG)","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eCorrects tracking errors and opto-mechanical flexure\u003c\/li\u003e\n\u003cli\u003eLarge 8 × 14 mm prism for bright guide stars\u003c\/li\u003e\n\u003cli\u003eSlim 12.5 mm body thickness preserves back focus\u003c\/li\u003e\n\u003cli\u003eSupports main imaging cameras up to APS-C sensor size\u003c\/li\u003e\n\u003cli\u003eIncludes M54 and M48 telescope adapters\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\u003eSVBONY SV238 Off-Axis Guider (OAG)\u003c\/h2\u003e\n\u003cp\u003eThe SVBONY SV238 Off-Axis Guider delivers exacting tracking accuracy by integrating a large 8 × 14 mm prism into a slim, 12.5 mm thick body. This design eliminates the differential flexure common with separate guidescopes, making it essential for long-exposure imaging with sensors up to APS-C format. With native M54 and M48 interfaces and a 1.25-inch port for guide cameras, the SV238 provides a rigid, precise connection in complex imaging trains.\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\u003eEliminating Flexure: The Advantage of an 8x14mm Prism\u003c\/h3\u003e\n\u003cp\u003eFor long-focal-length imaging, the greatest threat to sharp stars is differential flexure between the main telescope and a separate guidescope. The SV238 OAG solves this by using an 8 × 14 mm prism to pick off a small portion of the main telescope's light path. Any tracking error or mechanical shift seen by your guide camera is the exact same error seen by your main imaging camera, resulting in perfectly round stars.\u003c\/p\u003e\n\u003cp\u003eThe large prism size ensures you can find a suitable guide star even in sparse star fields, illuminating guide sensors from 1\/3\" to 1\/1.8\" effectively. This removes the need for a heavy, flexure-prone guidescope, simplifying your setup and improving overall image quality.\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\u003eA Slim 12.5mm Profile for Modern Imaging Trains\u003c\/h3\u003e\n\u003cp\u003eBack focus is a critical and often limited resource in astrophotography. The SV238 OAG is engineered with a main body thickness of just 12.5 mm, consuming minimal space in your optical train. This slim profile allows you to easily incorporate other essential accessories like filter wheels and rotators while still reaching focus with your main camera.\u003c\/p\u003e\n\u003cp\u003eThe total optical path length is determined by the adapter used, with the M48 adapter adding 4 mm and the M54 adapter adding 5 mm. This compact and rigid CNC-machined aluminum body is designed to support cameras with sensors up to APS-C without causing vignetting on the guide prism.\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 Adjustments for Pinpoint Guide Stars\u003c\/h3\u003e\n\u003cp\u003eAchieving optimal guiding requires precise focus on the guide star. The SV238 features a dedicated helical focuser for the 1.25-inch guide camera port, allowing for smooth, backlash-free adjustments to get your guide stars perfectly sharp. A sharp guide star enables your software to calculate centroids more accurately, leading to sub-pixel guiding corrections.\u003c\/p\u003e\n\u003cp\u003eFurthermore, the prism height is adjustable, allowing you to fine-tune its position. You can move the prism deeper into the light path to capture brighter stars or retract it to avoid vignetting the main sensor, providing the flexibility needed for various telescope and camera combinations.\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\u003eBroad Compatibility: M54, M48, and 1.25-inch Connections\u003c\/h3\u003e\n\u003cp\u003eThe SV238 is designed for maximum compatibility with common astrophotography equipment. It includes both M54 and M48 threaded adapters for connecting to a wide range of flatteners, reducers, and focusers. For connecting to cameras or filter wheels with smaller threads, M54-M42 and M48-M42 adapters are also included in the box.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eTelescope Interface:\u003c\/strong\u003e M54 and M48 adapters included for direct connection to your imaging train.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eGuide Camera Interface:\u003c\/strong\u003e A standard 1.25-inch holder with a helical focuser accepts most planetary and guide cameras.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCamera Support:\u003c\/strong\u003e Provides an unvignetted guide field for main imaging cameras with sensors up to the APS-C format.\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\"\u003eWhat is the total optical path of the SVBONY SV238 OAG?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe total optical path length depends on the adapter you use. The main body of the SV238 OAG is \u003cstrong\u003e12.5 mm\u003c\/strong\u003e thick. To this, you add the thickness of the telescope-side adapter: the \u003cstrong\u003eM48 adapter is 4 mm\u003c\/strong\u003e and the \u003cstrong\u003eM54 adapter is 5 mm\u003c\/strong\u003e. Therefore, the total path length is 16.5 mm with the M48 adapter and 17.5 mm with the M54 adapter.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I set up the SV238 OAG with an SCT and an APS-C camera?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eFor a Schmidt-Cassegrain Telescope (SCT) with a standard rear cell thread, you will typically need a reducer\/flattener that outputs an M48 or M54 thread. First, attach the appropriate adapter (M48 or M54) to the telescope side of the SV238. Then, connect your APS-C camera to the other side, using any necessary spacers to achieve the correct back focus for your flattener. Finally, insert your 1.25-inch guide camera into the helical focuser port and adjust both the prism height and helical focuser to get a sharp image of a guide star.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill the 8 × 14 mm prism on the SV238 vignette my main camera sensor?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe SV238 is designed to work with main camera sensors \u003cstrong\u003eup to APS-C format\u003c\/strong\u003e without the prism obstructing the main light path. The prism height is also adjustable, allowing you to retract it slightly if you notice any shadowing on your flat frames, ensuring a clear field for your primary imaging camera.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan the SV238 OAG find a guide star for imaging faint targets like the Pelican Nebula (IC 5070)?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. The large \u003cstrong\u003e8 × 14 mm prism\u003c\/strong\u003e intercepts a significant amount of light, increasing your chances of finding a suitable guide star, even when pointed at areas away from the dense Milky Way core. For a target like the Pelican Nebula, pairing the SV238 with a sensitive guide camera (recommended size \u003cstrong\u003e1\/3\" to 1\/1.8\"\u003c\/strong\u003e) should allow you to locate a guide star without issue.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat guide cameras are recommended for the SVBONY SV238?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe SV238 is optimized for guide cameras with sensor sizes ranging from \u003cstrong\u003e1\/3\" to 1\/1.8\"\u003c\/strong\u003e. This range includes popular and sensitive monochrome guide cameras that are well-suited for picking up faint guide stars through the OAG prism. The guide camera should have a standard 1.25-inch nosepiece to fit the helical focuser.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhy should I use the SV238 OAG instead of a separate guidescope?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eAn OAG like the SV238 eliminates the problem of \u003cstrong\u003edifferential flexure\u003c\/strong\u003e. This is when the main telescope and a separate, externally mounted guidescope physically shift slightly relative to each other during an exposure, causing elongated stars. Because the OAG uses the same light path as the main camera, it guides on the exact same motion, correcting for tracking errors, mirror flop, and tube flexure simultaneously.\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\u003ePrism Size\u003c\/td\u003e\n\u003ctd\u003e8 × 14 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOAG Body Thickness\u003c\/td\u003e\n\u003ctd\u003e12.5 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eApplicable Main Camera Sensor\u003c\/td\u003e\n\u003ctd\u003eUp to APS-C\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eRecommended Guide Sensor Size\u003c\/td\u003e\n\u003ctd\u003e1\/3\" to 1\/1.8\"\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTelescope Interface\u003c\/td\u003e\n\u003ctd\u003eM54 \/ M48\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eM54 Adapter Thickness\u003c\/td\u003e\n\u003ctd\u003e5 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eM48 Adapter Thickness\u003c\/td\u003e\n\u003ctd\u003e4 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMain Camera Interface\u003c\/td\u003e\n\u003ctd\u003eScrew Connection\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eGuide Camera Interface\u003c\/td\u003e\n\u003ctd\u003e1.25 inch with Helical Focuser\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003ePrism Height Adjustable\u003c\/td\u003e\n\u003ctd\u003eSupported\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\"\u003eSV238 Off-Axis Guider Body\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eM48 Adapter\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eM54-M42 Adapter\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eM48-M42 Adapter\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\/svbony-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eSVBONY 1-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"SVBONY","offers":[{"title":"Default Title","offer_id":52861226189085,"sku":"SV-W9196A","price":99.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/SVBONY-Off-Axis-Guider-OAG-SV238-1_2de77cc6-de5b-4aea-951d-e2d295b77122.jpg?v=1788659524","url":"https:\/\/davidastro.com\/en-us\/products\/svbony-sv238-off-axis-guider-oag","provider":"David Astro","version":"1.0","type":"link"}