HOW TO COLLIMATE A SCHMIDT-CASSEGRAIN TELESCOPE

[@ericbarnett6771]

I recently acquired a late 80's Meade 8" SCT. Planetary views through it have been less than amazing with the planets looking "soft" at higher mags. This video is the simplest, and most straightforward, explanation of how to collimate an SCT that I have found. Thank you, Tsula!

[@tsulasbigadventures]

Thank you! I hope getting good collimation helps improve the views through your SCT.

[@thierrymartin8378]

You have a classical Meade which is easy to collimate. The ACF version is another story. But the only available option to collimate is the same.

[@GalvestonCountyMike]

Thank you Tsula! On my 10" Newtonian collimation assembly, I replaced the screws with ones having knobs from Bob's Knobs. This way, I don't drop the hex wrench down my tube onto the mirror! Cheers from Texas!

[@tsulasbigadventures]

That's a good idea for a Newtonian reflector. On a SCT the screws are right out in front of the telescope. Cheers.

[@elray4932]

I have Bob’s knobs and they are great!

[@Astronurd]

@@tsulasbigadventures I fitted Bobs knobs on every SCT I’ve owned. Makes it easier and faster without having to faff around in the dark with Allen keys.

[@Dennis-tf2cs]

Bob's Knobs are great. Allen Keys and corrector plates don't mix well at all.

[@tsulasbigadventures]

@@Dennis-tf2cs I probably should have mentioned to be careful not to touch the corrector plate. Also I noticed a large blotch on the corrector plate. I will need to try to remove it with an air blower.

[@christopherhamm1574]

Brilliantly done. Great tutorial. Clear skies. Chris

[@tsulasbigadventures]

Thanks, Chris!

[@mcsew2k]

Turn what direction?

[@ThatDamnPandaKai]

I ended up replacing the screws on my Evo8 with thumbscrew to make for easier adjustments. I also find attaching it to a webcam (or DSLR) makes it much easier to collimate when you have a computer screen for better accuracy especially at higher magnification if you use an eyepiece projector.

[@jackjennings6143]

You're like the bob ross of telescopes :) love your energy!

[@tsulasbigadventures]

Bob Ross the painter?! Thank you very much!

[@ABCMO-bl5pi]

Tsula, thank you for a very clear and useful video. I am now viewing everything I can on collimation because of what happened last night. We had partly cloudy skies, so I decided to work on my Celestron C6’s collimation, which I knew needed adjusting from the appearance of stars in an earlier astrophotography session. So I adjusted it, but in the wrong way. I took the airy disk that looked more or less like the image at 7:11 of the video to one that was worse than the (2) diagram at the 6:40 point in the video! It took me 90 minutes to make the collimation this bad (used Arcturus as the star, by the way). I gave up and realized I should have really reviewed everything about how to do this beforehand before proceeding (give someone enough rope . . .). I do have one question. It seems like a lot of other KZbin videos say to loosen two of the screws if you are going to tighten one. Your advice seems to be to tighten one and loosen the other. Any thoughts about this? Again, thank you for this information.

[@tsulasbigadventures]

That depends on whether you try to tighten a screw and it won't give. In that case you shouldn't try to turn that screw at all. Never try to force any of the screws. Go to the next screw and loosen it before proceeding. I hope that helps.

[@ABCMO-bl5pi]

@@tsulasbigadventures Thank you. I need all the help I can get!

[@tsulasbigadventures]

@@ABCMO-bl5pi You're welcome. I hope you get it straightened out.

[@douglasthompson9482]

Great ideas…thank you Tsula.

[@tsulasbigadventures]

Thanks. I'm glad you found it useful.

[@przemyslaws1346]

❤ Super video.. great explained..and great sense of humour 👍🤩🤩

[@tsulasbigadventures]

Thank you so much!

[@gregerianne3880]

Great video, Tsula! Thanks so much for all the terrific information. Haven't had to collimate my EdgeHD8 yet, but now I'm ready! 😀

[@tsulasbigadventures]

Thanks. I rarely have to collimate my Meade. It doesn't get moved far from the garage and the JMI Wheeley Bar is very stable even over snow. How do you like the Edge HD8 so far?

[@gregerianne3880]

@@tsulasbigadventures I really like it, Tsula! I've gotten a couple of very good, close up, images with it and I think I've ironed out most of the wrinkles. (I have to send this one back, per Celestron, since there was some 'stuff' on the primary mirror I reported to the vendor and Celestron (to their credit) wants to ship me a new one without the schmutz. Okay by me, except for having to disassemble and reassemble all my peripherals again.) The mirror debris doesn't seem to to be interfering with images or visual use, though. But the scope itself it great. Not nearly the dreamy simplicity and ease of use of my refractors, but it's all a great learning experience and I'm very happy with the results so far!

[@tsulasbigadventures]

@@gregerianne3880 I'm happy to hear that. That's great. How could something get on the primary mirror? I noticed there is a big blob on my 12" SCT. I was shocked when I saw it on the video. I need to get that off! Totally different topic: do you use an electronic focuser?

[@gregerianne3880]

@@tsulasbigadventures I haven't got a clue how that stuff got on the primary mirror, Tsula! I initially thought they were scratches and I took some photos to send the vendor. When I looked closely at the photos, some of the stuff looked like dead bugs, and the other debris/scratches(?) I have no idea about. The vendor sent the photos to Celestron and they gave him an RMA to return the scope. It's just that the 8" Edge scopes out of stock everywhere, so it might be mid-October or so before a replacement arrives. I thought these scopes were pretty much sealed like refractors, but I guess not. The blob on Artemis is on the corrector plate (I hope)? That's funny, I was going to remark how clean your corrector plate looked on the video! 😀 I've had to clean my Edge corrector plate about 3 times already. (I've been using an air blower, camel hair brush, and then a sensor cleaning kit/swab to clean it and it comes out pretty good.) Yes, I use ZWO electronic focusers (EAFs) on the Edge as well as my refractors, the 107PHQ and AT60. It took some adjustment on the Edge (for me in the ASIAir adjusting step size and exposure of the EAF) until I got the autofocuser settings correct, but I can't imagine imaging without it to be honest. I also bought a Tri-Bahtinov mask that's supposed to be better than a standard Batinov mask for both focusing as well as collimation, but I haven't had a chance to try it out yet. I was going to check the accuracy of the EAF with it, but from the images I've gotten the EAF is pretty darn accurate.

[@tsulasbigadventures]

@@gregerianne3880 I was thinking about it last night and wondered if something could get inside on the primary mirror when you remove the visual back but I'm not sure. I'm going to work on cleaning Artemis today since it's cloudy. I looked into an electronic focuser but it seems like no one makes one for a Meade unless you alter the EAF made for Celestron SCTs. I watched a video on how to do that but I am not that handy and would be worried about damaging the focus knob. Guess I will just keep manually focusing for now. Take care.

[@craiglowery4427]

Thank you Tsula for the great tips. I never thought about letting the OTA cool down first. Any tips on selecting the correct second screw? I collimate with my camera in place of the eyepiece. Then I watch the image on my laptop as I adjust the screws on my Celestron 14" Edge HD. I check my collimation at the beginning of every session. Some people check theirs continually through the night. My scope with its mirror locks holds collimation well.

[@tsulasbigadventures]

You're welcome. That's a good idea about using the laptop with a camera or you could flip the screen on the camera to face you but that screen is much smaller than a laptop. I have never had my 12" telescope go out of collimation during an evening of viewing. It seems highly unlikely that would happen. In fact, my telescope rarely needs collimation.

[@elray4932]

Yet another very informative video! Would be cool to see a collimation video on a refractor. There is not much information out there. Granted, most don’t and probably won’t ever need collimation. But still rough shipping and handling or a rough ride to the observing site might knock it off kilter. Also, it would be great to check the collimation to ensure you are getting the most out of your expensive refractor. 😊

[@tsulasbigadventures]

Thanks, Elray. I have never collimated a refractor before. I would need to research it.

[@Dennis-tf2cs]

Refractors are generally best collimated by the manufacturer or someone who does it professionally and has the right equipment. Most of them will do it for a nominal fee (you pay shipping), it's not something I'd recommend attempting unless you have the right equipment. Leave this to the Pro's.

[@gregerianne3880]

I have to agree with Dennis - leave this to the Pro's. Too many things can go wrong when you fiddle with a refractor's innards.

[@elray4932]

@@gregerianne3880 Yes, completely agree yet the higher end refractors have adjustment screws.

[@gregerianne3880]

@@elray4932 Yes, they do! For me, anyway, since I haven't got a clue about what I'm doing, that comes under the heading of "give someone enough rope and they'll hang themselves." 🤣

[@Michael.Chapman]

Love watching your presentations :-) I’ve lost much observing time using this collimation technique, as shown in most manuals, over the decades. Am now using precision artificial stars (of various sizes) placed as far away from the scope as possible, for reasonable coarse collimation. This can be done on a dull day-and there’s no need to track. Loved your smooth defocused star image-much information on the optical quality of SCT mirrors is gained by examining and comparing the centered, defocused stellar image on both sides of focus. Many people now seem to advocate a triBhatinov mask (plus overlay), to simplify collimation-is this actually easier than the basic technique?

[@tsulasbigadventures]

Thank you. I thought about getting an artificial star and trying that out during the day. I have never used a triBahatinov mask to collimate. Is it different from a Bhatinov mask? I have one that fits my 12" SCT. I will have to look this up and see how it works.

[@lazerman121]

I have a Vintage Celestron C8 and I think my primary mirror is crooked. There is a tube inside coming out from the primary (I assume for glares) and when I look through the eyepiece hole without the eyepiece I can see in the reflection that it is crooked and the entire reflection seems to be crooked. Is it possible to move the primary mirrors?

[@tsulasbigadventures]

Well, what I am explaining in this video is how to move the primary mirror by making slight adjustments to the collimation screws on the piece of plastic in the center of the primary mirror (at the front of the telescope). Before you adjust those screws you shouldn't rely on looking through the eyepiece holder without an eyepiece but actually look at a star and defocus the star to see if it is lopsided. If it is that's how you know that the primary mirror is crocked. Your collimation screws move the primary mirror but just a little bit. Moving the screws too much could make it fall out. I am not sure what that tube is that you mentioned.

[@Johnnybox81]

Assuming you haven't dropped the scope down the stairs, how often do you collimate? I've had a Mak-Cass 127mm for about 8 years and never collimated!

[@tsulasbigadventures]

I have never collimated it. I check it often and it's always perfectly round with the airy disc in the middle. I don't think you can collimate a Mak-Cass. At least my Orion Star Seeker IV, 150mm Mak cannot be collimated.

[@Johnnybox81]

@@tsulasbigadventures you can on the secondary of the 127 mak but not the primary mirror. There's 6 screws at the back, 3 to hold and 3 to adjust. With these scopes my mantra is; if it looks fine, don't touch it :)

[@TasmanianTigerGrrr]

What distance should i place an artificial star from the telescope, and 11 inch cpc?

[@tsulasbigadventures]

You don't have to place it very far. Maybe 50 yards or so. That should be good enough.

[@jackfrost4033]

When you have identified with your finger the narrowest area of ​​the disc, should you turn the screw nearby clockwise or counterclockwise? thank you paul

[@tsulasbigadventures]

There are two ways to figure that out. One way is to just turn counter-clockwise or clockwise and see if the direction you chose made the circles more concentric or worse. The other way is to turn the mount on and then using the arrow keys at the slowest slew speed move the star to the edge of the field view in the same direction as the darker (thicker) area of the disc and then turn the screw while looking at the star and the star will move across the field. If the star moves out of the field of view then you are turning the wrong way.

[@jackfrost4033]

@@tsulasbigadventures 👍😊

[@garryfreemyer7187]

What if i don’t have a 100 or 300 times magnification eyepiece?

[@tsulasbigadventures]

Well you can use whatever eyepiece you have. It's just that if you can magnify it more you can get even more precise collimation.

[@rodysk8]

finally a video that explain the way supposed to be! mine Meade Etx 4" was better than mine Meade 8" LS in all aspect now i know why! thx for the video!

[@tsulasbigadventures]

Thank you!

[@MrLostsync]

Thanks for your explanation. I live in Brazil, I dont speak well, but let´s go. I have exactly the same telescope as yours, LX90 Meade 305mm SCT ACF. I can't collimate the telescope so that both the intra-focus and extra-focus are perfect. If one is perfect, the other is imperfect, and vice versa."When I say intra-focus I am using the focus adjustment knob in the way that I am moving the primary mirror from bottom to up, and when I say 'extra-focus,' I'm moving the primary mirror from top to down. Theoretically, the image from intra-focus and extra-focus should be the same. If one is correct the other should equally correct. But In my case it is not. Do you know something that I could do? Have you test your collimation for intra-focus and extra focus to know if both are ok? I don´t know if you understand my explanation.

[@tsulasbigadventures]

If I am understanding you correctly, it sounds like the telescope may have some astigmatism, which you can test for by racking in and out of focus in both directions. If the pattern is not identical then the telescope might have astigmatism. If that is the case, and I'm not exactly sure that is what you are describing, then it would have to be corrected at the factory. Is the telescope still under warranty? I don't believe you can correct for astigmatism with collimation. Do stars appear misshapen when you focus? That is a sign of astigmatism also.

[@MrLostsync]

@@tsulasbigadventures The telescope is no longer under warranty. I've had a Celestron SCT telescope before and i´ve never had this collimation issue. Yesterday, I was trying to improve the collimation, and the night was a bit turbulent, so I couldn't evaluate the stars in focus. I'll wait for a night with less turbulence. But thanks, I will continue trying to improve the collimation.

[@tsulasbigadventures]

@@MrLostsync I hope you get it figured out. When the seeing is bad it is very difficult to collimate.

[@garryfreemyer7187]

Thanks kindly Tsula!

[@tsulasbigadventures]

You're welcome. Thanks for watching.

[@JohnkelzRiggs]

You can hang a silver bulb Christmas ornament for a tree and catch the Sun's reflection

[@tsulasbigadventures]

OK. I didn't think about that. I was wondering if I should buy an artificial star.

[@3dfxvoodoocards6]

That’s why I only own refractors :))

[@billtomlinson317]

It's hard to take this video as instructional looking at the camping knife used to make adjustments.

[@tsulasbigadventures]

That's not a camping knife; it's all of the hex sizes folded on one tool. It works and that's the main thing.