A Bahtinov mask only works if it fits, and "fits" is where most people get tripped up. The good news: you need one measurement, one ruler, and about thirty seconds.
Step 1: Decide what you're focusing.
Camera lens or telescope? Our camera lens masks and telescope masks come in different size ranges, so start there. If you shoot both, you may need two masks, or one Tri-Bahtinov in a size that fits both.
Step 2: Measure the outside diameter where the mask will sit.
Our clip-on masks grip the outside of your lens barrel, dew shield, or telescope tube. Measure straight across the front, at the widest point, where the mask will clip on. No calipers? Wrap a tape measure or string around it, then divide that number by 3.14. Close enough to pick a size.
If you use a dew shield, measure the dew shield, not the tube underneath. That's where the mask lives.
Step 3: Pick the range that includes your number.
Every clip-on mask is adjustable within its listed range, using three soft-tip screws that hold it in place without scratching your gear.
One exception: the Kase filter. The Kase Bright Star doesn't clip on. It screws onto your lens's filter thread, so it's sized by the number printed on your lens (look for the Ø symbol, like Ø77 or Ø82), not by outside diameter. Those two numbers are not the same, and mixing them up is the single most common sizing mistake we see.
Size chart: camera lenses
| Product | Fits | Price |
|---|---|---|
| Bahtinov Mask for Camera Lenses & Telescopes (aluminum) | 60-90 mm, 80-120 mm, or 100-160 mm outside diameter | $29.99 to $39.99 |
| Carbon Fiber Bahtinov Mask, Made in the USA | 65-100 mm outside diameter | $29.00 |
| Kase Bright Star Magnetic Filter | 77 mm or 82 mm filter thread | $139.00 |
| Tri-Bahtinov Mask | 60-90 mm or 90-160 mm outside diameter | $33.00 to $37.00 |
Size chart: telescopes
| Product | Fits (outside diameter) | Price |
|---|---|---|
| Tri-Bahtinov Mask | 160-210, 220-270, 270-330, or 330-380 mm | $42.00 to $90.00 |
| Large Bahtinov Mask for 10-inch Telescopes | 250-270 mm | $57.50 |
| Large Bahtinov Mask for 12-inch Telescopes | 290-340 mm | $62.99 |
Common questions
My measurement falls in two ranges. Which do I pick?
Either will fit. If you plan to use the mask on a second lens or scope later, measure that one too and pick the range that covers both.
My telescope says "8-inch." Isn't that the size?
Not quite. "8-inch" is the aperture, the size of the mirror or lens inside. The tube around it is wider. Always measure the outside.
My lens is bigger than 160 mm.
That's big glass. Our telescope-sized masks start at 160 mm, and they work on large camera lenses just as well.
I measured and I'm still not sure.
Email us at Support@bahtinovmask.com with your lens or telescope model and your measurement. We'll tell you which one fits.
Not sure which type of mask you need? See Bahtinov Mask vs. Tri-Bahtinov vs. Kase Filter. Already have one? Here's How to Use a Bahtinov Mask.