Fits 8-1/2''-11-1/2'' 216mm-292mm. Aluminum full aperture Bahtinov focusing screen [AZ-503]

Astrozap: This Astrozap Bahtinov Focus Mask fits telescopes with a 8.5" to 11.5" (216 mm - 292 mm) outside diameter range. Thinly designed for consistently superior performance, this full aperture aluminum Focusing Screen is lightweight and features modifiable plastic screws for fixing to the outside of an optical tube.
In order to take advantage of your valuable telescope time, every observer (light side) and imager (dark side) knows that sharp focus is of utmost importance. The Bahtinov Focus Mask's unique diffraction pattern display provides higher precision in determining the best focus point, leading the Bahtinov to recently eclipse the Hartmann mask in popularity. When swapping eyepieces while observing, the Bahtinov mask offers faster, more accurate focusing. For those interested in imaging, where obtaining the best images depends on camera focusing, the Bahtinov mask eliminates the need to guess the best focus point location and allows quick modifications when changing filters or adjusting focus, enabling a smooth imaging session through the night.

Proudly manufactured in the USA, Astrozap Bahtinov Focusing Masks consist of solid sheet aluminum, making them a great deal more durable than their plastic counterparts available elsewhere. They are powder coated for corrosion resistance and to keep their attractive look. Astrozap has focusing screens that fit telescopes in all the most common sizes with adjustable plastic screws mounted in rubber grommets that help fit it in place without scratching or causing damage to the outside of the optical tube. Ideal focus is achieved time after time with the Bahtinov Focusing Mask's unique diffraction pattern.