Collimation, and why it matters
- Written
- JAN 2026
- Intended audience
- Optics nerds, Service techs
A pair of binoculars is really two small telescopes strapped together, and the whole thing only works if both of them are pointed at exactly the same spot. Not close to the same spot. The same spot. When they're lined up, your brain takes the two images and merges them into one without you noticing. That merging is something your eyes do all day anyway, so it costs you nothing. Lining those two tubes up is called collimation, and it's one of the most important aspects of a binocular's quality and ability to last generations.
You feel it before you see it
When the two tubes drift out of alignment, you usually don't see a double image. Your eyes just quietly work harder, pulling the two views together so the picture still looks normal.
The error is tiny — small fractions of a degree — but your eye muscles are holding that correction the entire time you're looking. After twenty minutes you get a headache, or your eyes feel tired, or you just find yourself not really wanting to use them. Almost nobody connects that back to the binoculars, because the view looked fine.
So a misaligned pair doesn't announce itself. It just becomes the pair you stop reaching for due to a subtle misalignment.
Set by hand, then protected by the body
Alignment gets dialed in at the end of assembly. An experienced assembler and technician looks through the finished instrument, judges the merged image, and adjusts until the two axes are genuinely parallel using special instruments and consistent visual targets. It's an experienced making the call, not a machine hitting a number, since these instruments are hand assembled by experienced craftsmen in Japan.
After that, the only thing keeping it there is the housing. Every knock, every hot car, every minor bump and temperature / pressure change puts a small load on the structure holding the prisms in place. A rigid body absorbs that and the alignment stays put. A flexible one lets it move a little at a time, and hands the problem back to you a few years later.
This is the practical reason to care what a binocular is made of. It isn't about scratches.
No amount of good glass fixes it
You can put excellent lenses and the best coatings available into a pair, and none of it helps if the two sides disagree about where they're pointing. Coatings affect how bright and clear the image is. Collimation decides whether looking through it is comfortable at all.
It's the specification you can't see in a photo, can't read off a box, and notice immediately when it's missing.