Check the listing for details. Astrophotography Bahtinov Mask DSLR Lens, Filter Sizes 49-127mm Tabbed Version. Condition: New. Listed at 14.00 USD. These are high quality Bahtinov masks with a high Bahtinov factor for easy focusing. They're 3D printed using premium quality American made black plastic. These masks have tabs that sit loosely in a DSLR lens thread, this means the mask comes off easily and won't disturb your setup. If you check my other auctions I also have this available in orange. Please see photos for example of using the mask. Depending on the size of mask you order it may appear larger than the gallery images, you will receive the size you specified. I have created models for all common thread sizes but I can also do custom oddball thread sizes if requested so feel free to message me with any requests. Bahtinov factor is calculated using the focal length divided by slot spacing. Here are some example factor numbers of my masks based on different focal lengths. 135mm = around 168 bahtinov factor200mm = around 250 bahtinov factor500mm = around 626 bahtinov factor Generally anything over 150 will allow you to focus easily. If you have any more questions or requests please feel free to message me. I ship out within 1 business days.