High Precision Tri-Bahtinov Mask: Focus and Collimation Tool

Focus and collimate with one tool. The Tri-Bahtinov is our highest precision mask. A standard Bahtinov mask tells you when you're in focus. The Tri-Baht tells you that, plus whether your telescope is properly collimated, using a single bright star and a few minutes of your setup time.

How it checks collimation

The Tri-Baht is three Bahtinov masks in one, arranged 120 degrees apart. Each produces its own diffraction pattern, for 16 easy-to-see spikes in total. On a well-collimated telescope, all three patterns reach perfect focus at the same focuser position, with every center spike sitting dead center at once. If one pattern is centered while another is off, your optics are tilted. Rotate the mask so each pattern lines up with a collimation screw, and you'll know exactly which screw to adjust.

Clips on, clips off

The mask clips to the outside of your telescope tube or dew shield with adjustable soft-tip screws, so it goes on and comes off easily in the dark without bumping your polar alignment.

Specifications

Choosing your size

Measure the outside diameter of your tube or dew shield where the mask will sit, then pick the range that includes it.

Collimating with the Tri-Baht

1. Center a bright star in your field of view and keep it centered throughout.
2. Rotate the mask so one pattern lines up with one of your collimation screws.
3. Focus until one pattern's center spike is perfectly centered.
4. Adjust the collimation screws to center the other two patterns.
5. Refocus and repeat until all three are centered at the same focus position.

For Newtonians, do a rough collimation with a laser or Cheshire first, then use the Tri-Baht for final fine-tuning on the primary mirror. For the full walkthrough, including SCT tips and troubleshooting, see our step-by-step collimation guide.

Care

Store the mask out of direct sunlight and never leave it on a hot surface or in a hot car. Like all acrylic, it can warp with heat.

Frequently asked questions

What is a Tri-Bahtinov mask?
It's three Bahtinov focusing masks combined into one, arranged 120 degrees apart. You get precise focus plus a collimation check in a single tool.

Which telescopes can I collimate with it?
Schmidt-Cassegrains, Newtonians, Ritchey-Chrétiens, and other Cassegrain designs. Refractors and camera lenses rarely need user collimation, so on those the Tri-Baht works as a high precision focusing mask.

Does it replace my laser collimator?
For Newtonians, no. Use your laser or Cheshire for rough alignment, then the Tri-Baht for final fine-tuning on a real star at focus, which is where collimation matters most. For SCTs, many owners collimate entirely with the mask.

Could something other than collimation throw a pattern off-center?
Yes. Camera or focuser tilt can produce a similar result. If collimation adjustments aren't bringing the patterns together, check your imaging train for tilt. Atmospheric seeing also makes the center spike shimmer, so use short exposures and judge the average position.

Does it work on camera lenses?
Yes, for focusing. The 60-90 mm size fits many telephoto lens barrels.

Do I remove it before imaging?
Yes. Once focused and collimated, unclip the mask. It comes off without disturbing your alignment.

When do the 90-160 mm and 330-380 mm sizes ship?
These sizes are on backorder and ship in 2 to 3 weeks. You can order them now.

Can I get replacement screws?
Yes. The Tri-Baht uses the same soft-tip screws as our other clip-on masks, sold in packs of three.