{"product_id":"optolong-clear-focusing-filter","title":"Optolong Clear Focusing Filter","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eAchieve Critical Focus with Dim Stars\u003c\/li\u003e\n\u003cli\u003eTransmission \u0026gt;98.5% Across the Visible Spectrum\u003c\/li\u003e\n\u003cli\u003eλ\/4 Transmitted Wavefront for Image Integrity\u003c\/li\u003e\n\u003cli\u003eParfocal with Other 1.85mm Optolong Filters\u003c\/li\u003e\n\u003cli\u003eFunctions as a High-Quality Sensor Dust Shield\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\u003eOptolong Clear Focusing Filter\u003c\/h2\u003e\n      \u003cp\u003eThe Optolong Clear Focusing Filter is a dedicated utility filter designed to solve one of astrophotography's most persistent challenges: achieving perfect focus with dim stars. By passing over 98.5% of visible light, this filter ensures your focusing star is as bright as possible, a critical advantage when narrowband or light pollution filters would otherwise render it nearly invisible. Constructed from B270 glass with a transmitted wavefront of λ\/4 and a thickness of 1.85mm, it maintains the optical path's integrity, allowing you to focus with confidence before swapping to your imaging filter.\u003c\/p\u003e\n    \u003c\/div\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"DAV-bg-danger\"\u003e\n      \u003cdiv class=\"DAV-section-center\"\u003e\n          \u003ch3\u003e\n\u003csvg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewbox=\"0 0 512 512\" style=\"width: 20px; height: 20px; fill: currentColor; margin-right: 8px; vertical-align: text-bottom;\"\u003e\u003cpath d=\"M256 32c14.2 0 27.3 7.5 34.5 19.8l216 368c7.3 12.4 7.3 27.7 .2 40.1S486.3 480 472 480H40c-14.3 0-27.6-7.7-34.7-20.1s-7-27.8 .2-40.1l216-368C228.7 39.5 241.8 32 256 32zm0 128c-13.3 0-24 10.7-24 24V296c0 13.3 10.7 24 24 24s24-10.7 24-24V184c0-13.3-10.7-24-24-24zm32 224a32 32 0 1 0 -64 0 32 32 0 1 0 64 0z\"\u003e\u003c\/path\u003e\u003c\/svg\u003eCritical Safety Warning: Not for Solar Use\u003c\/h3\u003e\n          \u003cp\u003eThis filter is \u003cstrong\u003eNOT\u003c\/strong\u003e designed for solar observation. Looking at the Sun with this filter, or any filter not explicitly certified for safe solar viewing, will cause immediate and irreversible eye damage, including permanent blindness. Do not point your telescope at the Sun with this filter attached.\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\u003eAchieve Critical Focus with \u0026gt;98.5% Transmission\u003c\/h3\u003e\n      \u003cp\u003eNarrowband and aggressive light pollution filters drastically dim incoming starlight, making it difficult for autofocus routines to lock on or for you to judge manual focus accurately. The Optolong Clear Filter solves this by passing more than 98.5% of light across the entire 420-680nm visible spectrum. You simply use this filter to achieve a sharp, bright focus on a star, then swap it for your narrowband or LRGB filter to begin imaging, knowing your focus is already set.\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\u003eParfocal and Protective with λ\/4 Wavefront Flatness\u003c\/h3\u003e\n      \u003cp\u003eA focusing aid is useless if it degrades your image or shifts the focal point. The Optolong Clear Filter is made from B270 substrate polished to a λ\/4 transmitted wavefront with 30s parallelism, ensuring it won't introduce aberrations. Its 1.85mm thickness makes it parfocal with other Optolong filters of the same thickness, minimizing the need to refocus after a filter change. It also serves as an excellent dust shield, protecting your camera sensor or reducer optics from dust during long imaging sessions.\u003c\/p\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\"\u003eWhy do I need the Optolong Clear Focusing Filter? Can't I just focus without a filter?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eWhile you can focus without a filter, adding a narrowband or LRGB filter into the optical path will slightly shift the focal point. The Optolong Clear Focusing Filter has a thickness of \u003cstrong\u003e1.85mm\u003c\/strong\u003e, designed to be parfocal with other Optolong filters. By focusing with this filter first, you ensure the focal point is correctly set for when you swap to your imaging filter, saving time and guaranteeing sharp results.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eIs the Optolong Clear Filter the same as a Luminance (L) filter?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eNo. A Luminance filter is an imaging filter with specific UV and IR blocking characteristics. The Optolong Clear Filter is a utility filter designed purely for focusing. It passes a wider band of light (\u003cstrong\u003e\u0026gt;98.5%\u003c\/strong\u003e from 420-680nm) to maximize star brightness for focusing software and visual confirmation. It is not intended for capturing final image data.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the Optolong Clear Filter help when imaging the Horsehead Nebula (B33) with a narrowband filter?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eImaging Barnard 33 requires a strong Hydrogen-alpha filter, which blocks almost all starlight except for a single wavelength. This makes focusing stars extremely dim and difficult. With the Optolong Clear Filter, you can select a nearby bright star like Alnitak, achieve perfect focus using the full visible spectrum, lock your focuser, and then switch to your Ha filter to capture the faint nebulosity without struggling to see the dim, red-only star.\u003c\/p\u003e\n  \u003c\/div\u003e\n    \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eWill the Optolong Clear Filter improve focusing with my modified DSLR and f\/5 Newtonian?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eYes. A modified DSLR is more sensitive to a broader spectrum of light, and this filter's \u003cstrong\u003e\u0026gt;98.5%\u003c\/strong\u003e transmission takes full advantage of that. In an f\/5 Newtonian, stars will be bright and sharp through the Clear Filter, allowing your camera's live view or focusing software to achieve a much more accurate focus than with a light pollution or narrowband filter installed.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eCan I leave the Optolong Clear Filter in the optical train as a dust shield?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eAbsolutely. With its high-quality \u003cstrong\u003eB270\u003c\/strong\u003e substrate and \u003cstrong\u003eλ\/4\u003c\/strong\u003e wavefront, it will not degrade your image quality. It acts as an effective barrier, preventing dust from settling on your camera sensor or reducer optics during a long imaging night.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use the Optolong Clear Filter for solar viewing?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003e\u003cstrong\u003eNO. ABSOLUTELY NOT.\u003c\/strong\u003e This filter provides no protection from the Sun's harmful radiation. Using it for solar observation will cause instant and permanent blindness. Only use filters specifically designed and certified for safe solar observation.\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\u003eSubstrate\u003c\/td\u003e\n\u003ctd\u003eB270\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eThickness\u003c\/td\u003e\n\u003ctd\u003e1.85mm\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eAverage Transmission\u003c\/td\u003e\n\u003ctd\u003e\u0026gt;98.5% (420-680nm)\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eSurface Quality\u003c\/td\u003e\n\u003ctd\u003e60\/40\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eTransmitted Wavefront RMS\u003c\/td\u003e\n\u003ctd\u003eλ\/4\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eParallelism\u003c\/td\u003e\n\u003ctd\u003e30s\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eAvailable Sizes\u003c\/td\u003e\n\u003ctd\u003e1.25\" Mounted, 2\" Mounted\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\"\u003eOptolong Clear Focusing Filter (Selected Size)\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\/optolong-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eOptolong 3-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Optolong","offers":[{"title":"1.25\" Mounted","offer_id":52941924565277,"sku":"OPT-12401","price":34.0,"currency_code":"CAD","in_stock":true},{"title":"2\" Mounted","offer_id":52941924598045,"sku":"OPT-12402","price":42.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Optolong-Clear-focusing-filter-is-designed-to-highly-pass-the-visible-spectral-region-420-680nm-at-98-5-transmission-1_d5f8835e-290b-416b-b60e-680f79a67a1a.jpg?v=1789592420","url":"https:\/\/davidastro.com\/products\/optolong-clear-focusing-filter","provider":"David Astro","version":"1.0","type":"link"}