Fits 2-1/2''-5-1/2'' 63mm-139mm. Aluminum full aperture Bahtinov focusing screen. [AZ-501]

Astrozap: Lightweight full aperture aluminum focusing mask with adjustable grommets for telescopes that have an outside diameters of between 2.5" and 5.5" (63 mm to 139 mm). Thin construction enables ideal performance.
Imagers as well as observers know that to make the most of their valuable telescope time, sharp focus is crucial. In terms of popularity, the Bahtinov-style mask has recently surpassed the Hartmann mask because of its novel diffraction pattern display which enables higher accuracy in determining the optimal focus point. For dark side imagers, where achieving the finest images is reliant upon camera focusing, the Bahtinov mask simplifies the process of finding the ideal focus point so you don't have to estimate anymore. Additionally, quick adjustments can be made when exchanging filters or fixing focus as your imaging session progresses through the night. For light side observers, the Bahtinov mask provides quicker, higher precision focusing, even when switching eyepieces.

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.