How To Collimate A Refractor
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- Опубликовано: 2 окт 2024
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I used a card board box, aluminum foil, and a house lamp. Very carefully with a very sharp needle, poked a small hole in the a/f, as small as possible, cut a 3" circle in the card board box, taped the a/f over the hole in the cbb. Ran an extension cord 300', put the lamp on a small stool, put the cbb over the lamp, make sure no other light escapes except thru the the pin hole. At night, had my refractor firmly bolted down 300' away. Using the lowest power lens, focused on the pin hole. Once focused, went to a higher power lens and slightly defocused it. Then looking thru the lens, I saw rings that were not centered. Then started messing with the 3 focusing screws till I saw a perfect bulls eye (as best as you can). The only problem I had was when I tried tightening the 3 screws (to make sure the lens does not move) next to the focusing screws. It took me 4 nights to get it correct. a/f = aluminum foil cbb = card board box
Hi ! Finally a great turorial on refractors collimation! Love your channel, very
technical !
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
Do not use a laser to collimate a refractor, refractors are collimated with a Cheshire and can be done in daylight.
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.
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.
Excellent!
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.
Thank you for the information, very interesting!
Hello,didn't knew that refractors need collimation too,but i guess it applies for apochromatic refractors,until now i knew that only newtonians need collimation
All optical systems need to be properly collimated.
Nice video! out of cuirosity is that 3rd printer in your affiliate link something that you use for yourself too as a 3d printer or you use another 3d printer? :) Thinking of buying one.
Right now, I am using only one 3D printer. If you happen to purchase a 3D printer from Amazon (it does not have to be SOVOL SV06), please click on my affiliate link right before. Thanks!
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!
You will have to open the file using FreeCAD (which is free to download) and from there, you can export to STL. Watch this video as a quick intro: ruclips.net/video/02CWCsGPJ-s/видео.html. Clear skies!
@@darkskygeek Thank you very much! I will try that
I have an AstroTech 80mm ED doublet grab and go scope I use with a Twilight One Mount. Carry it in my king cab truck wherever I go. So far so good.
I'm a retired engineer and have shims to .001 of an inch with .1mm being .004". for those who can only afford a reflector with a poor focuser I add the following.
I bought an inexpensive 102mm tabletop reflector with a poor focuser I shimmed until it was centered and drilled and tapped holes in the plastic housing and put nylon screws to hold the focuser tube in place within .002 inch or .05mm instead of that wiggle it did before. My grandsons use it and use a laser collimator to keep the secondary in place as Zhumell's primary on the 102 cannot move. Really pathetic focuser. You can buy shims, taps and drill bits at an auto parts store if you have a bad focuser on a reflector.
Very informative video, the way you have explained it really makes it easy to understand, thanks for the research & explanation 👍
Thank for this tutorial. I have a question on illuminating the cheshire eyepiece - what is the best way to do this? Dark room with a narrow beam of light ? Does the light have to be perfectly perpendicular to the cheshire eyepiece? Thank you
You’re overthinking it 😁 As long as you put the telescope cover on the dew shield, you can work in a well lit room. And for the light source, a simple LED work light placed on top of the opening of the cheshire eyepiece will work just fine. CS!
@@darkskygeek I must be doing something wrong then. I can only think it must be the backfocus from the 10mm x 70mm FL lens. Does it have to be exactly 70mm from the glass to the camera? Or does this vary per scope. I’m trying to collimate an 80mm f6 ES. thanks again for
@@paskoh It depends on the lens you picked up and installed into the cheshire projection device. If it has a 70mm FL, then yeah, the sensor should be close to 70mm behind that little lens. Hope this helps!
@@jlecomte0719 thank you
Great video, I already have a Cheshire eye piece, but I don't have a 3d printer, is there anyway you could make me one of those projection adapters for me to purchase ? or would that open too much of a Pandora's box ?
It would open Pandora’s box. Nevertheless, I highly recommend owning a 3D printer, not just because it’s a ton of fun, but also because it is so useful! And they have become pretty inexpensive in recent years. CS!
@@darkskygeekno worries, yeah… a 3D printer is nowhere in the cards for us, I’ll ask around to see if any of my friends have one. Keep up the great work
There are a lot of 3D printing services out there, you just need the file.
@@aagifford cool, thank you
It's a big objective and a collimatible lens cell seems like a luxury. My armored binoculars with their smaller lenses not so much.
Thanks for this. It's very informative.
Hello Julien, where is the link to the German website describing the Gryzbowski-Style Collimator. Thanks!
Oops! I just added it to the description. Just in case, here is the link: www.fernrohr-service.de/4.html
Nice analysis and process. Thanks for adding to the hobby.
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?
The artificial star I purchase was cheaper than the ones from Hubble, and was indeed smaller (20 microns) which allows me to use it in my garage, with only 4 or 5 meters of distance. Thank you for the kind words!
Very interesting video! Subbed
At 5'20" you mentioned a 10mm lens. Where in the assembly is that placed?
It’s a 10mm diameter lens. It is placed inside the small circular cavity at the top of the DIY adapter.
Here's a plausible explanation of the centering screws in the lens cell: They indeed do serve to center align the lenses, and this process should be done *prior* tightening the retaining ring, otherwise and accident could happen. Once the retaining ring holds the mirrors in the lens cell, the centering screws have served their purpose and, to eliminate any pinched optics, they should be unscrewed a little bit.
Yes, I think you are exactly right!
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.
Exactly right!
Excellent video, like!
Perfectly simple and easy!
👍👍👍👍 Excellent job. Thank you!
Great content as always
Wow ! You are quite the inventor !
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