Every observer (light side) and imager (dark side) know that sharp focus is essential for getting the most out of precious telescope time. Recently, the Bahtinov-style mask has overtaken the Hartmann mask in popularity for the reason that the Bahtinov diffraction pattern's unique display provides a more accurate guide to determining the optimum focus point. For light side astronomy, the Bahtinov mask enables faster, more precise focusing when changing eyepieces. For dark side astronomy, where camera focusing is critical to obtaining the best images, the Bahtinov mask eliminates the guesswork in locating the point of best focus and permits quick adjustment when changing filters or tweaking focus as the imaging run continues through the night.
Astrozap's unique Focusing Cap designs fit most telescopes and performs a dual function. The cap itself contains three holes at a calculated points around the perimeter of the cap. When the center knob is rotated, the inside panel lines up with the holes to create the Bahtinov pattern that admits starlight, creating the unmistakable Bahtinov diffraction spikes that enable determination of the best focus point. Turn the center knob again, and the inside panel rotates, closes the holes, and converts the focusing cap into a dust cap. All Astrozap Focusing Caps are proudly made in the USA out of solid aluminum, and powder coated to resist corrosion and retain their handsome appearance for years to come. As one imager discovered, it is good to have an Astrozap Focusing Cap handy because one never knows when the electric focuser will quit.
Not everyone wants or needs a dust cap, so Astrozap manufactures the classic Bahtinov mask. Like the Focusing Cap, the Astrozap Focusing Screen is proudly made in the USA out of solid sheet aluminum (unlike others' offerings made of plastic and not nearly as durable) and also powder coated to resist corrosion and retain its attractive appearance. Also, like the Astrozap Focusing Cap, Astrozap has many sizes of Focusing Screens to fit telescopes in most popular sizes. The Astrozap Focusing Screen is designed with plastic screws mounted in rubber grommets that adjust to fit the outside of the optical tube, holding the screen in place without marring or scratching the tube's finish. The Focusing Screen produces the same unique Bahtinov diffraction pattern as the Focusing Cap and enables the same result: best focus every time.