Not sure this is the right mask for your telescope? Use our Focus Mask Finder — match your scope to the right Standard, Tri-Bahtinov, or Hyperstar/RASA mask.
Adjustable Bahtinov focus mask for OTAs from 3.5" to 6.5" front aperture. Sets onto the front of your telescope, gives you perfect focus in seconds, and lifts off cleanly when you're done. The adjustable peg system fits any scope in this aperture range — including OTAs we don't make a custom-fit mask for. Made in our own shop in the USA — American materials, American machinery, by Americans.
Fits any OTA with a front aperture diameter from 3.5" to 6.5" — refractors, small Newtonians, compact astrographs, and any scope in this size range we don't offer as a custom-fit.
Why a Farpoint adjustable Bahtinov
- Universal fit, 3.5" to 6.5". The adjustable peg system seats securely on any OTA in this aperture range, including brands and models we don't make a custom-fit mask for.
- Made in the USA. Designed and manufactured in our own shop with American materials, American machinery, and American workmanship.
- Indestructible ABS plastic. Won't crack, warp, or shatter like aluminum or acrylic alternatives. Built to last decades.
- 15+ year track record. Farpoint has been making focus masks longer than nearly anyone in the hobby.
What's in the box
- 1× Farpoint Adjustable Bahtinov Mask
- Adjustable peg system for 3.5" to 6.5" OTA range
- Instructions for use
How a Bahtinov mask works
Place the mask over the front of your telescope and aim at a fairly bright star. Take a short exposure. You'll see three diffraction spikes — two angled spikes forming an X, plus a third central spike that's offset to one side or the other when the scope is out of focus. As you adjust the focuser, the central spike moves across the X. When it lands perfectly centered and symmetrical, you've hit optimum focus. Lift the mask off and start shooting.
A star coming into focus through a Bahtinov mask
Free software for precise focus measurement
If you want machine-precise focus instead of eyeballing the spike pattern, free open-source software can analyze the diffraction image automatically:
- Bahtinov-Collimator — a Windows tool that quantifies focus error directly from your image. Available on GitHub.
- APT (Astro Photography Tool) — Bahtinov mask analysis is built into APT's image-capture workflow.
Bahtinov-Collimator analyzing a star image for precise focus measurement
Want collimation help too? Step up to the Adjustable Tri-Bahtinov
The Tri-Bahtinov mask uses three different grid patterns to reveal both focus AND collimation errors in a single exposure — same adjustable peg system, more capability. See the Adjustable Tri-Bahtinov for 3.5" to 6.5" OTAs →
Related guides
- Focus Masks Buyer's Guide — material comparison, custom-fit vs adjustable, choosing the right type
- Telescope Collimation Guide — full walkthrough on collimating your scope
The unmistakable diffraction spike pattern at perfect focus
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