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A Tri-Bahtinov mask for SCT collimation and focusing

astrophotography imaging SCT
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#501 Psittacula

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Posted 21 November 2021 - 12:59 PM

I would like to add what I have attempted about Newtonian collimation using the tri-bahtinov mask.

 

First, I used a laser collimator to align the optical axis. In particular, I aligned the center mark on the primary mirror with the laser point. Then, for optical axis alignment using the tri-bahtinov mask, I basically used only the adjustment screws of the primary mirror. I did not use the adjustment screws of the diagonal mirror.

 

Satoru


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#502 Borodog

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Posted 21 November 2021 - 04:29 PM

Thank you both. I just ordered a pair of tri-Bahtinovs for my C8 and C11. Hopefully I can jerry rig the latter one to use with the 10" Dob.



#503 Borodog

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Posted 30 November 2021 - 03:51 PM

Thank you both. I just ordered a pair of tri-Bahtinovs for my C8 and C11. Hopefully I can jerry rig the latter one to use with the 10" Dob.

I got my masks yesterday. I collimated my C8 with one last night, and I just want to say, holy cow! What a revelation. Took me a few minutes to work out how it worked, but once I did, it was easy as pie. I followed these steps:

 

1) Get on a target star and get to rough focus.

2) Put on the mask, oriented such that the sections are aligned with the collimation screws.

3) Obscure the third of the aperture (more or less, doesn't have to be exact) next to a chosen screw, and observe on screen which axis changed in order to get oriented. Don't touch that screw (unless you run out of play in the others).

4) Focus the axis from number 3.

5) Adjust one of the other 2 screws, observe which of the 2 remaining axes changes, and which way the center line crosses that X.

6) Adjust the axis from 5 until the second axis is also in focus; refocus the first axis and re-center the star as needed.

7) Repeat 6 for the last axis.

8) Stare in wide wonder at the joy you have created.

 

I can't wait to collimate my 1100 EdgeHD tonight!


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#504 Procyon

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Posted 25 December 2021 - 07:07 PM

Hello there, I haven't collimated my 11" CPC 1100 in years, a couple of friends did it for me a few years past though. Quick question, do I need a camera to collimate with a Tri-Bahtinov mask? Or do you suggest I collimate the old school way?

 

Thanks



#505 cytan299

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Posted 25 December 2021 - 09:15 PM

Hello there, I haven't collimated my 11" CPC 1100 in years, a couple of friends did it for me a few years past though. Quick question, do I need a camera to collimate with a Tri-Bahtinov mask? Or do you suggest I collimate the old school way?

 

Thanks

I always use a camera because it's easier to stretch the image to see the spikes. But I only do imaging so if other people eyeball the spikes and it works, please chime in.

 

cytan


Edited by cytan299, 25 December 2021 - 09:31 PM.

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#506 MarMax

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Posted 26 December 2021 - 08:23 PM

Hello there, I haven't collimated my 11" CPC 1100 in years, a couple of friends did it for me a few years past though. Quick question, do I need a camera to collimate with a Tri-Bahtinov mask? Or do you suggest I collimate the old school way?

 

Thanks

You can collimate with the Tri-B mask visually. In some ways it's easier than with the camera. I'm still trying both methods and the key is good conditions. If conditions are only fair it's more difficult with either method.

 

My experience with the C11 and the Tri-B mask is it's great to easily get to 92-95% collimation, but that last 5-8% is difficult for me. I'm still waiting for a 4/5 seeing and 4/5 transparency evening to finish off that last 5-8%. 


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#507 Jinux

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Posted 03 January 2022 - 04:41 PM

Hello there, I haven't collimated my 11" CPC 1100 in years, a couple of friends did it for me a few years past though. Quick question, do I need a camera to collimate with a Tri-Bahtinov mask? Or do you suggest I collimate the old school way?

 

Thanks

Definitely with camera, mainly because you can watch the spikes while adjusting.

You can get easily frustrated if you have to keep back and forth between front of corrector and back of eyepiece, especially when you try this first time and don't know which knob and which direction turn will make which spike go which direction...



#508 Procyon

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Posted 14 January 2022 - 12:05 PM

Anyone know what the difference between these two TriBahtinov mask types are? Or if there is any difference at all?

 

https://farpointastr...oducts/fp412ht#

 

https://buckeyestarg...TriBahtinov.php



#509 Procyon

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Posted 14 January 2022 - 05:34 PM

https://satakagi.git...ensitivity.html

 

waytogo.gif


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#510 Acapulco Rolf

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Posted 27 January 2022 - 07:52 AM

I printed a Tri Bahtinov mask yesterday afternoon for my Edge C8 HD
Printed it in two halves to get it on my print bed.

I set the the z height for the mask to be 0.4mm
Each half printed in about 56 minutes

Did some brief tests with it last night

Cloud cover meant I only got about an hour of time under the stars last night

Hoping for clear skies to continue with this...

Thanks to Satoru, Cytan, Kirk, Jinux and all those from whom I've learnt new things in this forum thread

Some images from last night's session
 

Tri Bahtinov Mask

 

Tri Bahtinov mask focus-defocus Edge8HD 1422 203 F7
 
Capella Tri Bahtinov 26 01 2022  1 C8 F7 defocussed 1
 
Capella Tri Bahtinov 26 01 2022  1 C8 F7 NINA 1 1 defocussed  3
 
Capella Tri Bahtinov 26 01 2022  1 C8 F7 NINA 1 2
 
Capella Bahtinov mask focus 26 01 2022  1 C8 F7
 
Capella Tri Bahtinov edgehd8 26 01 2022 3
 
Capella Tri Bahtinov edgehd8 26 01 2022 5 1 1 In NINA  2
 
Capella Tri Bahtinov edgehd8 26 01 2022 5 1 1 In NINA
 
My 3d printed Tri Bahtinov mask
 


 


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#511 cytan299

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Posted 27 January 2022 - 08:22 AM

I printed a Tri Bahtinov mask yesterday afternoon for my Edge C8 HD
Printed it in two halves to get it on my print bed.

I set the the z height for the mask to be 0.4mm
Each half printed in about 56 minutes

Did some brief tests with it last night

Cloud cover meant I only got about an hour of time under the stars last night

Hoping for clear skies to continue with this...

Thanks to Satoru, Cytan, Kirk, Jinux and all those from whom I've learnt new things in this forum thread

Some images from last night's session
 

 

Thanks for posting this. Very nice. From your donut photos and the Tribahtinov photos, it looks like collimation is still a bit off in the 2 - 8 o'clock position like you showed.

 

One thing that bothers me, your dark ring around the Poisson spot looks odd. Maybe it'll be fixed with better collimation.

 

For demonstration purposes, you might want to focus in tighter so that only about 2 rings are shown after collimation is done. 

 

cytan


Edited by cytan299, 27 January 2022 - 08:25 AM.

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#512 Acapulco Rolf

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Posted 27 January 2022 - 08:41 AM

Yes, for sure
Can’t really do any actual collimation until skies permit

Last night was just a ‘first light’ excercise

Thanks for the tips :)

Edited by Acapulco Rolf, 27 January 2022 - 08:42 AM.

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#513 fortranguy

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Posted 07 February 2022 - 08:08 PM

Updated instructions available here: https://adaa4013-f92...07ccd3a50e8.pdf


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#514 JayScope

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Posted 07 February 2022 - 08:30 PM

Unfortunately none of the retailers include the mask cover - crucial piece needed for collimation.
Any suggestions as to a source?
Can someone 3d print or send me a regular file I can print out to paper and cut out and transfer that to a piece of plastic? I have a Meade SCT8". My tri-baht is from Farpoint.

#515 Borodog

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Posted 07 February 2022 - 10:14 PM

Mask cover? whatyoutalkinboutwillis.gif
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#516 Procyon

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Posted 07 February 2022 - 10:24 PM

Mask cover? whatyoutalkinboutwillis.gif

lol.giflol.giflol.giflol.giflol.gif



#517 JayScope

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Posted 07 February 2022 - 11:45 PM

Here ya go Arnold!

 

 

Attached Thumbnails

  • 67A237B5-D435-42A5-A4CB-34E49A99AFE1.jpeg

Edited by JayScope, 07 February 2022 - 11:46 PM.

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#518 charles.tremblay.darveau

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Posted 08 February 2022 - 12:36 AM

I got my masks yesterday. I collimated my C8 with one last night, and I just want to say, holy cow! What a revelation. Took me a few minutes to work out how it worked, but once I did, it was easy as pie. I followed these steps:

 

1) Get on a target star and get to rough focus.

2) Put on the mask, oriented such that the sections are aligned with the collimation screws.

3) Obscure the third of the aperture (more or less, doesn't have to be exact) next to a chosen screw, and observe on screen which axis changed in order to get oriented. Don't touch that screw (unless you run out of play in the others).

4) Focus the axis from number 3.

5) Adjust one of the other 2 screws, observe which of the 2 remaining axes changes, and which way the center line crosses that X.

6) Adjust the axis from 5 until the second axis is also in focus; refocus the first axis and re-center the star as needed.

7) Repeat 6 for the last axis.

8) Stare in wide wonder at the joy you have created.

 

I can't wait to collimate my 1100 EdgeHD tonight!

I ordered one but couldn't try yet due to months of non-stop rain (thank you pacific northwest weather...).  For clarification, does 'align section with collimation screws'  refer to the middle of the sections, or the section boundaries?



#519 Acapulco Rolf

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Posted 08 February 2022 - 02:26 AM

Unfortunately none of the retailers include the mask cover - crucial piece needed for collimation.
Any suggestions as to a source?
Can someone 3d print or send me a regular file I can print out to paper and cut out and transfer that to a piece of plastic? I have a Meade SCT8". My tri-baht is from Farpoint.

 

Satoru created a Tri Bahtinov mask cover generator online here

 

 

Tri Bahtinov mask cover generator
 
 
Convert the generated svg file into an stl for 3d printing

I'm figuring out how to "fill" the svg model of the cover in inkscape before I convert it into an stl file to make it 3d printable...

Tri Bahtinov cover In inkscape

 

Update

Loaded the Bahtinov cover svg file into Fusion360

Exported from Fusion360 as an stl file

Split the exported model into two to fit on my print bed 

 

Will print the model on my 3D printer later today 

 

Cover stl files attached here for anyone that wants to use them (for a C8 EdgeHD)

 

Cover now 3D printed smile.gif

Tri Bahtinov Mask Cover C8 EdgeHD

 

Tri Bahtinov Mask F360 C8 F10 Tinkercad
cover Tri Bahtinov Mask F360 C8 F10 right
cover Tri Bahtinov Mask F360 C8 F10 left
Tri Bahtinov cover in Fusion 360

 

 

Attached Files


Edited by Acapulco Rolf, 08 February 2022 - 11:32 AM.

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#520 Borodog

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Posted 08 February 2022 - 09:42 AM

Ah. I had no need for that as I already have regular masks.

CTD; I don’t think it matters as long as you align it somehow with the screws, ie not at some weird intermediate angle to them. Then when you cover one sector adjacent to one of the screws, the central line of one of the 3 sets will vanish, letting you know that that axis corresponds to that screw.
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#521 Jinux

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Posted 09 February 2022 - 01:14 AM

Ah. I had no need for that as I already have regular masks.

CTD; I don’t think it matters as long as you align it somehow with the screws, ie not at some weird intermediate angle to them. Then when you cover one sector adjacent to one of the screws, the central line of one of the 3 sets will vanish, letting you know that that axis corresponds to that screw.

My way of aligning mask to 3 adjustment screws is that putting inner (center spike) slot on opposite location of adjustment screw. I still need to use hand to correlate a spike set to which adjustment screw. But once this is done, right turn of screw will move center spice to 'up' (or right, or down) direction. This simplified adjustment direction and reduced time of collimation for me. YMMV.


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#522 Psittacula

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Posted 09 February 2022 - 07:10 AM

Satoru created a Tri Bahtinov mask cover generator online here

Oops, that cover is only for the improved sensitivity (2nd Modified) version.

You can also design a cover for the original tri-bahtinov mask, though in the case of the original pattern there may not be much need for it since it can be easily covered by hand. Still, I can make it available if requested.

Satoru


Edited by Psittacula, 09 February 2022 - 07:21 AM.

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#523 JayScope

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Posted 09 February 2022 - 08:26 AM

Thank you Satoru -- I was able to just make a cover manually after seeing the generator and just traced it using the mask itself and cut it out of cardboard. The cover works great!
It really makes collimation very easy by aligning the cover to the mask and orienting the mask/cover as shown in the directions. Much easier than holding a hand over the front of the scope to cover a portion of the mask. Very convenient to just spin the mask/cover to the next collimation knob and adjust and iterate.


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#524 Psittacula

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Posted 09 February 2022 - 09:08 AM

The cover for the original has been prepared.smile.gif

 TBMCss.png

 

Satoru


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#525 Acapulco Rolf

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Posted 10 February 2022 - 12:42 PM

The cover for the original has been prepared.smile.gif

 attachicon.gifTBMCss.png

 

Satoru

Thank you

 

Have generated a mask cover (Cytan's version) and 3D printed it 

 

3D printing stl files attached here for the cover for anyone that wants to print one for a C8 Edge HD

 

Tri Bahtinov Mask with Cytan cover C8 EdgeHD

Attached Files


Edited by Acapulco Rolf, 10 February 2022 - 01:02 PM.

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