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Custom-fit Tri-Bahtinov focus and collimation mask for the Celestron 9.25" SCT with Hyperstar/Fastar capability. Drops onto the front of your telescope, gives you focus AND a collimation check from a single short exposure, and lifts off cleanly when you're done. Made in our own shop in the USA — American materials, American machinery, by Americans.
Fits all Celestron 9.25" SCTs with Fastar/Hyperstar capability — including the Edge HD 9.25, CGEM 9.25, CGX 9.25, and EVO 9.25 OTAs.
Why a Farpoint custom-fit Tri-Bahtinov
- Drop-in fit, no fiddling. Sized specifically for the Celestron 9.25" SCT (Hyperstar/Fastar) corrector plate. Custom-fit matters more on a Tri-Bahtinov than a standard Bahtinov — an off-center mask can produce false collimation readings.
- 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.
- Two diagnostics, one tool. Focus AND collimation check from a single short exposure — no swapping masks, no second imaging session.
What's in the box
- 1× Farpoint Tri-Bahtinov Mask, custom-fit for Celestron 9.25" SCT (Hyperstar/Fastar)
- Instructions for use
How a Tri-Bahtinov mask works
A standard Bahtinov produces three diffraction spikes — two forming an X, plus a center spike that moves across the X as you focus. Land the center spike on the X, and you're focused. One pattern, one diagnostic.
The Tri-Bahtinov rotates that same pattern 120° around the center, three times. The result: three sets of diffraction patterns from one short exposure — three Xs, three center spikes, three independent focus reads at three different orientations.
For focus: adjust until all three center spikes land centered on their Xs. When all three are symmetrical, you've hit optimum focus.
For collimation: a properly collimated scope reaches focus at the same focuser position across all three orientations. An uncollimated one won't — light from different parts of the aperture takes slightly different path lengths to the image plane, so different orientations reach focus at slightly different positions. If one of the three Bahtinov patterns can't be centered when the others are, that axis is out of collimation, and the offset direction tells you which screw to turn.
Bonus for SCT owners: align the mask's three Bahtinov sections with your three secondary mirror collimation screws. You get a direct visual mapping between what you see on screen and which screw needs adjusting.
The Tri-Bahtinov design was developed by amateur astronomer CY Tan and shared with the astrophotography community on GitHub. Farpoint manufactures the masks; CY Tan invented the pattern.
Each of the three Tri-Bahtinov panels produces this pattern — three focus reads at three orientations, simultaneously, from one exposure
Free software for precise focus and collimation analysis
If you want machine-precise readings instead of eyeballing the spike pattern, free open-source software analyzes Tri-Bahtinov diffraction patterns automatically:
- Bahtinov-Collimator — a Windows tool that quantifies focus AND three-axis collimation 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 and collimation measurement
Just need focus, not collimation?
If your scope is already well-collimated and you only need focus assistance, our standard Bahtinov mask is the simpler (and less expensive) option — same drop-in fit, same precision focus, just the focus axis without the collimation diagnostic. See the Bahtinov for Celestron 9.25" SCT (Hyperstar/Fastar) →
Related guides
- Focus Masks Buyer's Guide — material comparison, when to use which type, why custom-fit beats adjustable
- Telescope Collimation Guide — full walkthrough on collimating your scope
The Bahtinov diffraction principle — multiplied by three for simultaneous focus and collimation diagnostics
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