Check the listing for details. 105mm Bahtinov Focus Mask for DSLR Lens - 2023 Clip-in Version. Condition: New. Listed at 18.00 USD. High quality Bahtinov masks with high bahtinov factor for easy focusing. Clips into any camera lens filter thread using a gentle spring loaded action. I have listings for all common lens thread sizes so please check my other listings if you need a different size. This is my new version for 2023 incorporating some design improvements.Filter size now embedded in print for easy identification.3 spring loaded clips instead of 4 for easier removal and better optical centering.Top surfaces now smoother with less layer lines visible.Bahtinov factor is calculated using the focal length divided by slot spacing. 50mm = around 62.5 bahtinov factor135mm = around 168 bahtinov factor200mm = around 250 bahtinov factor500mm = around 626 bahtinov factor Anything over 150 will allow you to focus easily with large diffraction spikes. A 50mm lens will still work with my masks but the diffraction spikes will be smaller. Not recommended for lenses under 50mm. 3D printed with premium American made plastic. I can also do oddball filter sizes and custom sized masks for telescopes and dew shields, feel free to message me with any requests.