Collimating a SCT with a Tri-Bahtinov Mask

I was recently asked by a subscriber if I could create a video explaining how to use a tri-bahtinov mask to collimate a Schmidt-Cassegrain telescope. So I hope this is helpful to all SCT users that are thinking of purchasing one of these focus/collimation aids.
Equipment used in this video:
Bob's Knobs Collimation Thumbscrews : www.bobsknobs.com/SCT/SCT.html
Farpoint Astro Tri-Bahtinov mask: farpointastro.com/collections...
Celestron Nexstar 8Se Schmidt-Cassegrain Telescope www.celestron.com/products/ne...
Celestron EdgeHD 8 Schmidt-Cassegrain Telescope: www.celestron.com/products/ed...
ZWO AsiAir Pro: astronomy-imaging-camera.com/...
ZWO ASI294MM Pro Cooled Monochrome Camera: astronomy-imaging-camera.com/...

[@hael8680]

You confused me. The spikes are clearly for adjusting the focus as you demonstrated by going out of focus. How did you do the collimation with the black piece of cardboard?? You didn't show that important step.

[@michelmoreno2140]

Thanks for this TUTO 🙏🏻 ! Clear and Helpful ❤

[@Cgconst1]

This is incredible!!! Thanks for this excellent and elegant solution. Awesome.

[@sandragayle7866]

Thanks Eric I just got my Celestron SE 6 Schmidt Cassagrain telescope. I do collimation on my older telescope like my red planet reflector telescope, but I am new to the Celestron SE 6. This was very informative appropriate it😊

[@wandaconde3696]

This is an excellent video of how this works. Thanks for putting this together.

[@simonworthington7461]

Cheers! I hadn't heard of the Tri Bahtinov mask so this is really helpful

[@bobbeanbags]

Awesome Eric! Thank you thank you thank you! Super clear explanation on how this works!

[@TheWonkyAstronomer]

Thanks for the collimation tips. I need to get one of those masks.

[@deuscaput]

Great video. I just picked up a tri-bahtinov mask and can't wait to dial in my collimation.

[@georgehatfield9473]

Thanks for the vidoe. I used the Tri-Bahtinov tonight to collimate my 8" Edge HD, and it worked like a charm. Great to have a video like this as a reference.

[@vincejenkins1143]

Very useful to see both the tri-bat mask & ASIAIR being used. Thank You!

[@Kailombian1]

A big thank you from Seattle. Fantastic video! 👨‍🚀

[@AstrowithEric]

Thanks for your feedback!

[@olly7248]

Really helpful, thanks for doing this 👍🏻

[@navyskiier]

Eric - just watched your video and it was excellent! Very thorough and well done!

[@AstrowithEric]

Thanks! Appreciate the feedback!

[@philippefenain4405]

This is a great video. Thank you so much from France !

[@AstrowithEric]

Thanks for the feedback!

[@anson22m]

Thank you! Eric Great video...I will be looking to order me one of these as well.

[@davidross4036]

Thanks, Eric! I was a bit intimidated until I saw your particular video, that walked me through the logic and the procedure!

[@MrFrost77]

Thanks for the awesome tutorial!

[@AstroVagabond]

Thank you for your video. I just order the Tri-Bahtinov mask. Much appreciated.

[@phillipsanchez6557]

Eric, this is the first time I've come across any of your videos. I found it very useful and well presented. I have very similar equipment and am looking forward to using the Tri-Bahtinov mask to get faster and better collimation. Looking forward to seeing more of your work. Thanks!!! Phil

[@philippefossier7178]

Good information and video. Thank you.

[@deltaquadrant5861]

Thanks Eric.

[@compubyte2010]

great video sir.. thank you for the information !!!

[@AstrowithEric]

Thanks glad it’s helpful to you. Clear Skies!

[@saskgrass]

Ordering mine now. I'm surprised this technique isn't talked about more often! Your explanation is much appreciated.

[@AstrowithEric]

Thanks David! Appreciate the feedback.

[@jimbundy8449]

Very cool! Thanks for posting.

[@AstrowithEric]

Glad you enjoyed it!

[@fotografiabymiguel]

A timely review. Enjoyed it, Eric. I just purchased an EdgeHD and will get one of these Tri Bahtinov masks. Looking forward to seeing more content.

[@AstrowithEric]

Thanks for the feedback! Clear skies!

[@gregscriba2655]

Thanks for doing this

[@ronlundgren4391]

Thanks Eric, I use the airy disk for doing my C8 but this will get it dead nuts. I’ll be adding to my wishlist. 🔭🍻

[@AstrowithEric]

Thanks for the feedback!

[@gerardford1116]

Great video Eric! I'm going to give this a go on my 10" Lx200 (which I know is out of collimation). Thanks again.

[@allenbaylus3378]

I would have liked to see some of your workflow - like using the black sheet to cover 2 of the screws to see what the single diffraction spike was doing - since I have never tried that before. it looks like you had a good sucess.

[@michaelclem3339]

That's awesome!

[@jongoldsby]

Thank you Eric for explaining this technique. I have the c8 with hyperstar and I suspect which switching modes may have resulted in miscollimation.

[@shoestringification]

great vid also love that tee shirt

[@stephenmcarthur2250]

Thanks I’ll try this next cloudless night

[@stevesteindorf2501]

Great Vid. Thx

[@Kijad]

Thank you so much for this video! I have read so many howtos on tribahtinov masks but they weren't particularly clear - I'm hoping to get everything really dialed in this evening if the skies hold!

[@Kijad]

I guess the joke here is "not particularly clear, much like my previous collimations" 😅

[@AstrowithEric]

Glad it was helpful!

[@jackdaniels2127]

Now I am convinced I need a tri mask for my Newtonian and the bolts too.

[@kevinburke8608]

This is great! I have a hard time judging the concentric circles… I’m close but never feels right the spikes would be a great help

[@AmatureAstronomer]

Thanks. Will do.

[@HeavenlyBackyardAstronomy]

Thank you, Eric. It's a challenge to collimate my C-11. I will try your method.

[@AstrowithEric]

Did it work?

[@edithtanguay8582]

Tank you!!!

[@brendanmanning1959]

Thanks

[@DawgcityClev]

Ordered one of these for collimating and waiting on the slow shipment.

[@lazylazyshark]

Great video. However in the image you show at min 7:38 as collimated, spikes do not look centered to me.. still the donought you get after defocusing looks nice and centered..

[@tomdaigon8707]

I was looking forward to seeing you actually doing the process. Why did you skip showing it and just jump to the end result?

[@JohnSmith-sm8oz]

Eric, question. I’m not exactly sure if I have a tri Batavia mask. It’s buried in my cabinet as I’m writing this and hard to get to, bu I was using it the other night on my 12” Meade, I get the 6 radial v’s with the spikes that you center, and in trying to center the center spikes I could get 4 but not all 6, then if I keep focusing I could get 2 but again not all 6, so it was one of the other, blew my mind at the time, now after watching your video I do believe it is a collimation thing, I’m going to try your process and see if I can get all 6 to line up, I’m thinking it’s a tri mask because my results look exactly like yours, if you have any ideas, I’d love to hear them, great video very helpful

[@gregerianne3880]

Super video, Eric! Thanks so much. When you first started and had the center spikes not between the outer spikes, I'm assuming you did a focus first. Do you use the ASIAir's autofocus first to get your best focus, or do you focus using the Tri-Bahtinov mask? If you do the latter, it seems that if you're out of collimation you wouldn't be able to get those center spikes to be in the middle of the other two, is that correct? I'm brand new to my EdgeHD 8 and I've installed a dew heater ring, but I've noticed that some of my stars have a spike (or tail) coming from one side, especially in the lower left and upper right corners. I'm not sure if this is because of the dew heater ring or something else. I've defocused on stars a couple of times to check my collimation and the secondary shadow appears to be in the center indicating that my scope is at least roughly in collimation. My question is whether I should have the dew heater ring on when I check/do my collimation? (I have a Tri-Bahtinov mask on order and I'm going to try it out when I get it.) Perhaps the Tri-Bahtinov mask will show the scope is not as collimated as I think. Appreciate your great videos! Thank you again.

[@josephluciani5531]

Eric, this is brilliant! I’ve struggled with collimation for years and your technique may be the answer I was looking for. As per one of the other comments, I’m not totally clear on the process. So, if I cover two screws, I’m now working with one screw and I believe you said that screw would effect one spike. Are you saying that if I loosen/tighten that screw, the “one” diffraction spike will become aligned and then you move on to a second screw and alignment? I realize my question is confusing, but if you could elaborate-perhaps going over exactly what your process was when you collimated….did you tighten/loosen one….move to another screw…check spikes, go back, etc. etc., Anyway, your videos are just fantastic…you always provide such wonderful advice. Please keep up the great work.

[@AstrowithEric]

Hi Joseph, if you are interested, I’m going to be on AstroWorld TV tonight and I’m going to share this question and do my best to answer it for you then. It might be a bit easier for me to explain that way vs writing it down here. We will be on tonight and hope you can join us. Thanks!

[@Zero_Point_Energy1]

Liked the video strictly based on the t-shirt.

[@rightarmofwyoming]

Are you in Preview mode, Focus, or something else on the ASIAIR? Thank you.

[@cyberblitz]

Those diffraction spikes are both manipulated by both focusing and collimation, so how do you do when to adjust each one?

[@michaelasbury5473]

Thank you so much for this video! I have an EdgeHD 800 that I thought was out of collimation so I installed Bobs Knobs which REALLY threw it out of collimation and I don’t think I’ve been in good collimation since. I have a tribahtinov mask on order and hopefully it’ll be here next week. One question I have is with the diffraction spikes, how do you know which knob to move? You mentioned covering up 2 of the 3 spikes. Maybe it’ll make more sense when I try it.

[@AstrowithEric]

sorry I meant cover 2 of the 3 screws. The screw you leave uncovered, should leave a one of the center diffraction spikes. So you’ll know then that spike is for that particular collimation screw and you can then start to adjust as needed.

[@michaelasbury5473]

@@AstrowithEric actually I said spike but I meant screw as well. :-) Thanks again! This video helps immensely! Clear skies!

[@MrGuitar50]

Great video! My issue is I have a new 9.25" Celestron SCT. There are no screws on the secondary mirror. Do I have to send it back to manufacturer or how can I otherwise fix it?

[@jasonschella7206]

Hi Eric, I'm just seeing this video now. Great explanation. One question I have is regarding the initial focusing. I assume you are autofocusing first without the tri-b mask and then the assumption is that any offset of the middle spike is then due to collimation error? Thanks, Jason

[@AstrowithEric]

Yes that is correct, I always perform an initial and and final autofocus after working with the tribahtinov mask and collimating.

[@alexandermassey5339]

Neat video. By the sounds of it a very innovative way of collimation. I have a couple of questions: How do you deal with mirror shift as this will spoil any collimation efforts? Are you using the scope's native focuser or an external one? Thanks, Alex.

[@AstrowithEric]

Yes I do have to collimate whenever I put the scope on the mount as I have an EAF right now and can’t lock the mirrors of my EdgeHD 8 until I can get a new auto focuser.

[@paulwilson8367]

Can this same technique be used on the RASA 8? You have or used to have one? I have star problems and wish to check this as a source. There is a tri made especially for the RASA 8, but I can't find a tutorial. I don't see any Bob's Knobs for a RASA.

[@lnewton46]

How can you know if the diffraction is collimation or poor focus

[@DeereX748]

How difficult is it to collimate optically using the tri-Batinov? By that, I mean using and eyepiece instead of doing it on a video screen? I've yet to get far enough into astrophotography to buy an astro camera or managing system, but will most definitely go with the ZWO products when I do. I have an Edge 8 and a shorty refractor (WO GT-81) and a couple of EQ mounts (AVX and EQ6R Pro).

[@geldingmakr]

Subscribed, but it still looked slightly out after you adjusted. Do you see that? Or is it just my newness to the hobby?

[@dfinchermd]

Great info, thanks. A few questions: Is focal reducer attached? Why Bin 4? How often do you collimate generally?

[@AstrowithEric]

I use Bin 4 for better visibility. I have collimated with the reducer and without. I collimate maybe every few months, it really depends as I do move my SCT on and off the mount often as I use other scopes. But this year for galaxy season it’s been on since early March and I have only done it once and its been locked in just fine.

[@davidshives1030]

Hi folks, so glad I found this. I'm at 5:01 in the video. I have a tri batinov, and if I am understanding this correctly all I need to do is cover up half of the face of the tribatinal mask. Meaning, 1/2 of the front of the telescope tube would be covered and the other half would be open. assuming that this would center where the small Bob's knobs would be. Does anyone have any videos or can confirm my understanding of this?

[@JeffFishman]

I bought a Bahtinov Mask - Celestron 8 SCT × 1, and use my new 8SE for visual only. Can I use this to collimate?

[@Ab20222]

Thank you for explaining this. Is it possible to use this method to collimate the primary mirror? And how do you know which mirror needs collimating?

[@AstrowithEric]

With a Schmidt-Cassegrain, only the secondary mirror (small mirror at front) is collimated, it will then be aligned to the primary mirror at the back of the telescope. The primary mirror is not collimated as it doesn’t move other than in/out for focus.

[@Ab20222]

@@AstrowithEric thanks for your clarification. I have a dobsonian.

[@Dennis-tf2cs]

Thanks Eric. I ordered my Tri-Bahtinov Mask last night after watching Astro World, Farpoint has already processed and is shipping, they are fast. One question, SCT's have a bit of mirror shift, is it critical to check the collimation after I do this and then take the scope off the mount while using another scope? Wondering if unmounting/moving the SCT will knock it out of collimation enough to worry about having to check it each time. Great video and thanks for the work that you do!

[@AstrowithEric]

IMO it never hurts to check when moving the OTA on and off the mount, I personally do, since I use the tri bahtinov for focusing and while Bobs knobs are great, you do tend to need to do collimation checks more often.

[@Dennis-tf2cs]

@@AstrowithEric yeah, Bob's knobs are nice. I'm going to see if there is a way to put a small spring on the threads to keep tension on then or something. I have them on my 8" Astrograph and they make it so much easier for collimation.

[@AstrowithEric]

@@Dennis-tf2cs let me know if you do get springs for the bobs knobs and how they work out. I’d be interested to hear about it.

[@KingHoborg]

Is it important that the B mask is as close to the camera lens as possible? I've been shopping around myself and have scouted out a mask that will fit over the hood of my lens but not the lens itself. Will that extra 4-5 cm of space make any difference in its effectiveness?

[@AstrowithEric]

I would put the Tri-Bahtinov over the SCT corrector plate, this is why it’s designed with the center hole to go around the secondary mirror, to be as close as possible to it. I would expect the spacing may make a difference.

[@Dudleydogg]

AT 7:14 in the video is where you stated the collumation is slightly off, how do you decide its collumation and not just Focus that has the spikes not centered? Is that because the spikes are out of alignment in different Directions? One is high one is low?

[@AstrowithEric]

As the diffraction spikes are not centered and I moved out of focus I could tell it was a bit off. I would make sure that they are centered as this tri bahtinov does double duty for focus and collimation. If you have a standard bahtinov mask you can use it to ensure best focus and switch back to the tri bahtinov to check for both.

[@astroworks]

Thanks Eric.. Great video.. will try this on my C14.. 1 question tho.. after you take the 1st image with the tribahtinov mask (5sec) how do you determine that it is out of collimation vs out of focus..

[@AstrowithEric]

Thanks for the feedback, although I don’t show it here, you can verify by using a standard focus mask. But I personally think that once you gain initial focus with the tri bahtinov even though the collimation spikes are a bit off because of being slightly out of collimation that I am in good focus. I do use my EAF afterwards to autofocus after my work to make sure I am in focus and test collimation a final time with the tri bahtinov.

[@astroworks]

@@AstrowithEric thanks Eric.. really appreciate your time here.. It is a very nice collimation technique 👌. Will order a mask soon 😀

[@davidcohn4755]

Just what I've been looking for, since I have the same exact setup. At time 7:00 in the video, the center lines in all 6 sets of spikes are displaced the same. How do you know which knob to adjust?

[@AstrowithEric]

By covering with my hand or sheet of cardboard/card stock one screws and that side of the scope the diffraction spike associated with that screw will disappear as it is blocked so that’s how I know what screw is associated with the diffraction spikes I see on the screen.

[@timmoody7600]

Eric, have you used a tri-bahtinov with metaguide for collimation? I realize you have AsiAir.

[@AstrowithEric]

I have not yet tried MetaGuide.

[@johnsuscavage7775]

Eric I was wondering what the difference is between a standard Batinov mask and a TRI- Batinov mask? I have one for my vintage C8 (1986) and noticed Your`s has the V sections you referred to in the video that my standard Batinov mask doesn`t. Will it still work for your collimination proceedure?

[@AstrowithEric]

Hi John, no the standard bahtinov mask will not work for collimating the SCT. The tribahtinov helps because you align with the screws and following the method I showed will help you get collimated. Thanks!

[@Kijad]

I think a standard Bahtinov mask will also only get your focus correct, but will not show you issues with collimation (there will only be the two spikes, not three iirc)

[@sophietaylor9753]

@@AstrowithEric You actually can use a standard Bahtinov mask; you have to align it to each screw, one after the other. It's a hassle, but you can do it.

[@msenin]

Does it matter if 3B mask is slightly tilted? I’ve wires sticking out of Celestron anti-dew heating ring that don’t let me set the 3B mask exactly on top of the corrector plate. I have Hyperstar, so it needs to be collimated on its own.

[@AstrowithEric]

I have the heater ring myself and just worked get as close as possible on the corrector plate.

[@msenin]

@@AstrowithEric Good to know

[@msenin]

@@AstrowithEric Does it make sense to focus with regular B-mask first and then switch to 3B mask for collimation, or focus and collimate at the same time? Like how can you tell it's already focused but collimation is wrong if central spikes are not dead-center? Do you expect that at least ONE of spikes would be centered if focus is achieved?

[@AstrowithEric]

I use the TriBaht for both focus and collimating.

[@AstrowithEric]

If there is one spike that if going through the center of the 3 in one of the sets i feel comfortable that I’m in good enough focus to begin collimating and once done I will check focus again. Im not usually so far out of collimation that it will affect my work on focusing.

[@bobbeanbags]

Have you tried this with your Hyperstar attached?

[@AstrowithEric]

I have the RASA 8 and it’s difficult to collimate as it doesn’t have the collimating screws like the hyper star so I haven’t tried it. Clear Skies!

[@starpartyguy5605]

The problem I have with your video is all we see is a collimated scope and in focus pattern. What does an out of collimated pattern look like? What does an out of collimation but focused pattern look like?

[@meeting69]

What is the difference between a bahtinov mask and a tri-bahtinov mask?

[@AstrowithEric]

A TriBahtinov is used for both collimating and focusing a SCT telescope. A Bahtinov is used just for focusing and can be used on all types of telescopes.

[@TheWonkyAstronomer]

First!

[@permafrost7781]

Awesome

[@peters6500]

Hi Eric, very good!- what helped me lot was an additional 2/3 cover for this tribahtinov mask: so its really easy to see which knob to turn; if you like see my post in the APT forum: aptforum.com/phpbb/viewtopic.php?f=19&t=4919 cheers, Peter

[@AstrowithEric]

Thanks Peter, very similar to what I shared in the video with using the card stock to cover 2/3 of the collimation screws.