How To Collimate A Refractor

Nice analysis and process. Thanks for adding to the hobby.

Hi ! Finally a great turorial on refractors collimation! Love your channel, very technical !

Wow ! You are quite the inventor !

Thanks for this. It's very informative.

Perfectly simple and easy!

Great content as always

This is a similar concept as the Takahashi collimating scope, which uses a small scope behind a Cheshire type diagonal flat, a magnifying eyepiece, and a sliding tube to change the near focus-- this is a novel function to let you shift the focus through the optical train. With a coaxial flat mirror in front (autocollimation), this adjustable near focus and magnification makes it quite easy to have very high precision using the human eye due to the additional reflections to use as reference. I have modified mine by using a cross hair magnification EP from a microscope, and a camera like you did. Even without a mirror, the magnification makes it easier to make more precise adjustment. Btw, many new Takahashi have no Collimation screws, just precise machining. Even fsq85 has no collimatable element for the front doublet.

Great video! I have an Esprit 80ED and have pinched optics. Have been looking for a detailed video like this to help me try to resolve the issue.

Very informative video, the way you have explained it really makes it easy to understand, thanks for the research & explanation 👍

Excellent video, like!

👍👍👍👍 Excellent job. Thank you!

Very interesting video! Subbed

Merci pour ce tuyau...encore ;)

Two TS refractors (80 and 102mm) I purchased had that iron cross artefact. Teleskop services refused to guide me along to get rid of the artefact on the 102mm. They said it would ruin the collimation. They however accepted that I returned the scope. For the second refractor (80mm), I decided to loosen those sets of 3 screws to the point where they started to feel loose. That fixed the iron cross issue. I tested it down to -10°C.

As a chronic refractor ATM'r, before any optical testing, I collimate the scope and check the collimation of any scope sent to me for testing. There is no reason to optically test a scope that is mis-collimated. For me, there are two physical collimations. The very first one is the focuser by using a quality laser in the focuser, hopefully, shining through a hole precisely centered in the middle of a paper mask placed over the objective. If the laser misses the hole by more than a mm or two, if I can, I adjust the focuser as best I can to make the beam pass through the hole. If I cannot make the adjustment, the scope goes back to the source. If it does "pass", I use a quality Cheshire to then, like you, makes sure the reflection dots merge to form a single dot. If not, and If possible, I then adjust the lens cell axial collimation screw sets to get them to line up. If there is no adjustment capability, and they are far enough off, the scope goes back to the source. Only after the scope "passes" those two tests, does the scope get optically tested (DPAC and star). If I see astigmatism in the star test, I will try to adjust it out with the axial collimation screw sets, even though it may then "fail" a subsequent recheck with the cheshire. After all, the goal is to have no astigmatism or coma at high power, at least for visual use. Best Regards Jeff

There are two ways to collimate a refractor lens. One, to adjust the tilt of the whole lens assembly relative to the focuser/cameras, and two to adjust the centring and sometimes even the tilt of the lens elements relative to each other. The impact in this case looks to have been partially mitigated by tilting the entire lens assembly, however it is clear from the star images that the lens elements themselves need to be adjusted relative to each other. This is usually achieved by means of a set of screws around the periphery of the lens cell which push into the lens elements. In this case they seem a bit tight and need slackening off maybe a 1/16th turn to see if that gets rid of the distortion. Then a star test is needed and the image is checked just before the airy disc changes to a point. There will be concentric rings which if broken on one side, will show coma or other effects.

It's a big objective and a collimatible lens cell seems like a luxury. My armored binoculars with their smaller lenses not so much.

Awesome video. Thanks a lot. Out of curiosity, are you using a 20 micrometers artificial star (as opposed to 50 microns from Hubble or 100 microns from astrozap) because of the shorter minimal distance? Or are there other considerations?

Wow! thank you for posting this. I was wondering if you had the DIY Chesire adapter save in another format (like .stl). I tried to open/download the file but it was 101 files in a format that my pc couldn't recognize/open. Thanks!

Hello Julien, where is the link to the German website describing the Gryzbowski-Style Collimator. Thanks!