Astrozap Focusing Cap w/ Built-in Bahtinov Focusing Mask For Most 152mm Aperture Refractors

AstroZap Focusing Cap with Built-In Bahtinov Mask – For Most 152mm (6") Refractors

Focusing a large refractor, especially for imaging, requires surgical precision—and the AstroZap Focusing Cap with Built-In Bahtinov Mask is just the tool for the job. Designed to fit most 152mm (6") aperture refractors, this two-in-one accessory gives you the accuracy of a Bahtinov mask and the protection of a dust cap in a single, field-ready solution.

Unlike separate masks that can get lost or damaged in transport, this design features a sliding internal shutter that reveals the integrated Bahtinov pattern only when you need it. During focusing, aim your refractor at a bright star and watch the classic three-spike diffraction pattern appear. Adjust your focuser until the center spike is perfectly aligned—and you're in critical focus. Once you’re dialed in, simply slide the shutter closed, and the cap resumes its role as a dust shield.

Whether you're shooting through an achromat or apochromat, the longer focal length and narrow focus range of a 6" refractor makes a built-in focusing tool like this one a huge advantage—especially when skies are changing fast or you’re swapping imaging filters.

Features:

• Fits most 152mm (6") aperture refractor telescopes

• Combines a protective front cap with a built-in Bahtinov focusing mask

• Sliding shutter mechanism keeps the mask protected when not in use

• Produces a clear diffraction pattern for fast, accurate focus

• Great for astrophotography, visual fine focus, or collimation checks

• Lightweight, durable construction designed for field use

Compatibility Note:

This focusing cap is sized to fit the dew shield/front cell diameters typical of 152mm refractors. It is not a universal fit—check your scope’s outside diameter for best results or reach out to us for fitment guidance.

Observing Tip:

With larger refractors, seeing conditions and thermal shifts can quickly affect your focus. A built-in Bahtinov mask lets you refocus in seconds without reaching for a separate accessory—perfect for imagers using filter wheels or motorized focusers who need to double-check sharpness on the fly.