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A Tri-Bahtinov mask for SCT collimation and focusing

astrophotography imaging SCT
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#476 Endymion

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Posted 24 August 2021 - 01:05 PM

I just purchased a tribahtinov mask (BuckeyeStarGazer's) for my C11 and gave it a try last night.  Image below seems to look good to me; can someone with experience tell me how good the collimation looks?

 

Thanks,

John

 

TriBahtinov C11HD


#477 cytan299

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Posted 24 August 2021 - 05:29 PM

I just purchased a tribahtinov mask (BuckeyeStarGazer's) for my C11 and gave it a try last night.  Image below seems to look good to me; can someone with experience tell me how good the collimation looks?

 

Thanks,

John

 

Looks great!

 

I'd suggest checking by removing the mask and going in and out of focus to see how the Airy disk behaves. You should see something like this:

 

https://www.youtube....h?v=Ie9j0Z9MNC8

 

This was as good as I could collimate my ETX125 using the TriBahtinov.

 

 

cytan


Edited by cytan299, 24 August 2021 - 05:32 PM.

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#478 Endymion

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Posted 24 August 2021 - 06:29 PM

Thanks cytan!



#479 Brain&Force

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Posted 08 September 2021 - 04:14 PM

I decided to try a custom design for a Tri-Bahtinov mask for my C5. Unfortunately, when I made the mask, I made the slot angles larger than I wanted (30 degree deviation rather than 15). However, the results were pretty good! I've taken to calling this mask the "Cheese Grater" since I'm currently in Wisconsin.

 

Here is the mask:

0lCcGPl.png

 

The diffraction spikes when defocused (note the splitting of alternating spikes, as well as the offset of the single spikes from the center). The resulting pattern has 3-fold symmetry.

DFTTKwa.png

 

When in focus, the spikes align and you get a perfect 12-fold diffraction pattern:

ehGWKyG.png


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#480 Whichwayisnorth

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Posted 12 September 2021 - 02:43 PM

Anyone have a working .stl for an 11" edgeHD?  the one I found early in the thread doesn't load with Cura.  And every "generator" link I click on says the page is not there any more.  Thanks



#481 cytan299

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Posted 12 September 2021 - 05:39 PM

Anyone have a working .stl for an 11" edgeHD?  the one I found early in the thread doesn't load with Cura.  And every "generator" link I click on says the page is not there any more.  Thanks

Doesn't this link work?

 

https://satakagi.git...i-Bahtinov.html

 

cytan


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#482 teashea

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Posted 12 September 2021 - 07:31 PM

Hi,

  I made a Tri-Bahtinov mask that I think would be useful for both SCT collimation and focusing. My mask is shown here:

attachicon.gifIMG_0086.jpg

 

The diffraction pattern that I see when I first point at Polaris is shown below:

attachicon.gifas_found.png

 

It is clear that 2 orientations are in focus while the third (indicated with red arrows) is not.

After collimation (still not quite perfect), I get all three orientations in focus

attachicon.gifcollimated.png

 

I built this mask because my judgement with the Airy disk method is not as objective as I would like it. I think by using my favorite tool, a Bahtinov mask, modified for collimation would make collimation much less subjective.

 

My full design and writeup can be found here:

https://github.com/c...299/tribahtinov

 

I hope this is useful for the community.

 

cytan

nice



#483 Psittacula

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Posted 13 September 2021 - 06:46 PM

Anyone have a working .stl for an 11" edgeHD?  the one I found early in the thread doesn't load with Cura.  And every "generator" link I click on says the page is not there any more.  Thanks

 

 

Doesn't this link work?

 

https://satakagi.git...i-Bahtinov.html

 

cytan

I'm not familiar with Cura, but it looks like these can be used to load SVG.
https://github.com/G...GToolpathReader
https://all3dp.com/2...printable-stls/



#484 ontherivet

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Posted 17 September 2021 - 10:38 AM

Anyone know if the grabber software is available anywhere at this point?

 

Thanks,

Don



#485 Psittacula

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Posted 19 September 2021 - 04:26 AM

Is there anyone who can write an "engraving generator"? that would be great..

I'm not sure what the effect of the engraved transparent mask is, but I've added the hairline option to the following generators
https://satakagi.git...ahtinovWebApps/
You may be able to create the desired pattern by combining the regular one with this hairline option.

Satoru

TBM hairline.jpg


Edited by Psittacula, 19 September 2021 - 04:31 AM.

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