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A Tri-Bahtinov mask for SCT collimation and focusing

astrophotography imaging SCT
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#76 DaveB

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Posted 22 December 2017 - 11:50 AM

I made a version of the tri-bahtinov mask to help me dial in the collimation on my Mak-Newt. I went with three Bahtinov masks but the straight and angled peices on opposite sides of the mask. Same principle just easier for me to draw up in CAD. I tuned the image using Maskulator and it worked wonderfully. It's really remarkable how perfectly Maskulator's simulations come out. What it predicted was exactly, I mean exactly what I saw in the eyepiece. 

 

I previously have been using software to dial in my final collimation and that takes a long time. The tri-Baht is much much faster and really quite an amazing tool when you really want to nail your collimation. Two huge thumbs up!

 

-Jim

Jim,

 

That looks like an interesting design. How did you come up with that idea? It looks like it would be easier to cut out than the other patterns.

 

Thanks,

Dave



#77 kingjamez  Happy Birthday!

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Posted 25 December 2017 - 10:12 AM

Thanks Dave. For this design, I really did the same thing as the OP, I just split the bahtinov mask in two and put each piece on opposite sides of the aperture. One side is the middle diffraction spike and the other side is the “angled” spike(s). It’s exactly the same pattern, just spread out more.

-Jim

Edited by kingjamez, 25 December 2017 - 10:12 AM.

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#78 cytan299

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Posted 26 December 2017 - 10:30 AM

 

I made a version of the tri-bahtinov mask to help me dial in the collimation on my Mak-Newt. I went with three Bahtinov masks but the straight and angled peices on opposite sides of the mask. Same principle just easier for me to draw up in CAD. I tuned the image using Maskulator and it worked wonderfully. It's really remarkable how perfectly Maskulator's simulations come out. What it predicted was exactly, I mean exactly what I saw in the eyepiece. 

 

I previously have been using software to dial in my final collimation and that takes a long time. The tri-Baht is much much faster and really quite an amazing tool when you really want to nail your collimation. Two huge thumbs up!

 

-Jim

Jim,

 

That looks like an interesting design. How did you come up with that idea? It looks like it would be easier to cut out than the other patterns.

 

Thanks,

Dave

 

There's many ways to skin a cat. The advantage of my design is that there are a lot more slots and so the diffraction pattern should be brighter. It turns out that a Japanese vendor is commercializing the mask:

 

http://reflexions.jp...n/archives/2280

 

And no, I don't make any money from this :)

 

cytan


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#79 James Cunningham

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Posted 22 January 2018 - 11:04 PM

how do you tell which collimation screw to turn?  Thanks

Jim



#80 cytan299

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Posted 23 January 2018 - 06:59 AM

how do you tell which collimation screw to turn?  Thanks

Jim

The instructions for using the mask are at:

 

https://github.com/c...rain-Telescopes

 

under section "Using the Tri-Bahtinov mask".

 

cytan



#81 James Cunningham

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Posted 06 February 2018 - 04:28 PM

Can some one direct me to where I can have a mask made?  Everywhere I called and explained what I wanted, they refused.  Thanks.

Jim



#82 cytan299

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Posted 06 February 2018 - 10:05 PM

Can some one direct me to where I can have a mask made?  Everywhere I called and explained what I wanted, they refused.  Thanks.

Jim

I sent mine to www.ponoko.com to be made.

 

cytan



#83 James Cunningham

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Posted 06 February 2018 - 11:21 PM

How much did it cost?  And what did you send to them?  Thanks

Jim



#84 cytan299

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Posted 07 February 2018 - 12:20 AM

I sent them an svg file. Cost is about $30. But that was 2 years ago.

 

cytan



#85 James Cunningham

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Posted 07 February 2018 - 12:23 AM

I want to get two of them.  One for my 11 inch SCT and another one for my 9.25 inch SCT.  Just what is an SVT file?  Thanks.

Jim



#86 cytan299

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Posted 07 February 2018 - 07:00 AM

svg is "scalable vector graphics". Since you have jpg files, it may be possible to vectorize them using online tools.

 

cytan



#87 A. Viegas

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Posted 16 February 2018 - 01:48 PM

If I wanted to try and cut one out of cardboard is there a pattern in .pdf that I can download and print out ? I can scale it for relevant aperture 8" and 11"?

Thanks
Al

Edited by A. Viegas, 16 February 2018 - 01:48 PM.


#88 James Cunningham

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Posted 16 February 2018 - 02:10 PM

No size for 11 inch but you can go to Office Depot and ask them to scale it up to 11 inch.  They will print it out for you.

Jim



#89 cytan299

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Posted 16 February 2018 - 02:22 PM

If I wanted to try and cut one out of cardboard is there a pattern in .pdf that I can download and print out ? I can scale it for relevant aperture 8" and 11"?

Thanks
Al

Please go to this link:

 

http://svg2.mbsrv.ne...i-Bahtinov.html

 

and the program generates whatever size mask that you want that will fit your telescope.

 

The format is in svg but a lot of programs can read svg and generate whatever file format that you like.

 

cytan


Edited by cytan299, 16 February 2018 - 02:23 PM.

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#90 A. Viegas

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Posted 17 February 2018 - 09:02 AM

 

If I wanted to try and cut one out of cardboard is there a pattern in .pdf that I can download and print out ? I can scale it for relevant aperture 8" and 11"?

Thanks
Al

Please go to this link:

 

http://svg2.mbsrv.ne...i-Bahtinov.html

 

and the program generates whatever size mask that you want that will fit your telescope.

 

The format is in svg but a lot of programs can read svg and generate whatever file format that you like.

 

cytan

 

Yes. I had seen that and I have tried it, but the .svg file it creates is not scaled to your typical 8x11 letter paper size to print out.  I have converted the .svg to .jpg and tried playing around with the scaling, but its not exact.  How can I print our a correctly scaled size drawing for a C8 and C11 SCT which I can then use as a mask to cut out a cardboard version?

 

Al



#91 cytan299

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Posted 17 February 2018 - 10:13 AM

 

 

If I wanted to try and cut one out of cardboard is there a pattern in .pdf that I can download and print out ? I can scale it for relevant aperture 8" and 11"?

Thanks
Al

Please go to this link:

 

http://svg2.mbsrv.ne...i-Bahtinov.html

 

and the program generates whatever size mask that you want that will fit your telescope.

 

The format is in svg but a lot of programs can read svg and generate whatever file format that you like.

 

cytan

 

Yes. I had seen that and I have tried it, but the .svg file it creates is not scaled to your typical 8x11 letter paper size to print out.  I have converted the .svg to .jpg and tried playing around with the scaling, but its not exact.  How can I print our a correctly scaled size drawing for a C8 and C11 SCT which I can then use as a mask to cut out a cardboard version?

 

Al

 

Sorry, I'm not sure how to do that because I've never done that before. However, I would suggest that you either install Inkscape, partition the result into pieces that can be printed on letter and then paste them together to form one large piece. And you can check that the dimensions are correct in Inkscape.

 

My other suggestion is to bring the file to kinko's and have them print it on a large scale plotter. IMO, that would be the easiest. And to make sure that the scale is correct, you might want to add a 1 inch square in inkscape to the svg file.

 

cytan


Edited by cytan299, 17 February 2018 - 10:14 AM.

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#92 Psittacula

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Posted 06 April 2018 - 10:44 AM

Hi, I tried collimation using tri-bahtinov mask with newtonian reflector. The tri-bahtinov mask seems useful for the final fine-tuning phase. The method is roughly as follows.

 

First of all, do an initial collimation with another existing collimation tool.

For example, if it is a laser collimator, adjust the secondary mirror so that the optical axis passes through the center of the primary mirror. Next, roughly adjust the primary mirror so that the laser light reflected from the primary mirror returns to the center of the collimator.

 

Next, remove that collimation tool and set up tri-bahtinov mask. At this time, match the orientation of the marks of the mask with the adjustment screws of the primary mirror. It is not those of the secondary mirror.

Then introduce a test star in the center of the field of view and focus. Be sure to evaluate the collimation with the test star always in the center of the field of view. This is the same for SCT.

 

The collimation using the tri-bahtinov mask after that is done only by adjusting the primary mirror. Because tri-bahtinov mask seems difficult to evaluate whether the optical axis passes through the center of the primary mirror.

 

The relationship between the adjustment screws of the primary mirror and the diffraction image looks the same as that of the SCT, so adjust it just like SCT.

 

Incidentally, newtonian has a spider so we can put a mask on it.

 

This is the diffraction image of tri-bahtinov mask with newtonian.

29663910_941219066036434_1696944629_n.jpg

 

Satoru


Edited by Psittacula, 06 April 2018 - 10:54 AM.

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#93 cytan299

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Posted 07 April 2018 - 04:13 PM

Hi, I tried collimation using tri-bahtinov mask with newtonian reflector. The tri-bahtinov mask seems useful for the final fine-tuning phase. The method is roughly as follows.

 

First of all, do an initial collimation with another existing collimation tool.

For example, if it is a laser collimator, adjust the secondary mirror so that the optical axis passes through the center of the primary mirror. Next, roughly adjust the primary mirror so that the laser light reflected from the primary mirror returns to the center of the collimator.

 

Next, remove that collimation tool and set up tri-bahtinov mask. At this time, match the orientation of the marks of the mask with the adjustment screws of the primary mirror. It is not those of the secondary mirror.

Then introduce a test star in the center of the field of view and focus. Be sure to evaluate the collimation with the test star always in the center of the field of view. This is the same for SCT.

 

The collimation using the tri-bahtinov mask after that is done only by adjusting the primary mirror. Because tri-bahtinov mask seems difficult to evaluate whether the optical axis passes through the center of the primary mirror.

 

The relationship between the adjustment screws of the primary mirror and the diffraction image looks the same as that of the SCT, so adjust it just like SCT.

 

Incidentally, newtonian has a spider so we can put a mask on it.

 

This is the diffraction image of tri-bahtinov mask with newtonian.

attachicon.gif 29663910_941219066036434_1696944629_n.jpg

 

Satoru

Hi Satoru,

   I've updated both the README and the wiki on my github page to include your instructions for collimating Newtonians. See 

 

https://github.com/c...rain-Telescopes

 

section "Using the Tri-Bahtinov mask for Newtonians (S. Takagi)"

 

and

 

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

 

section "How to use the mask"

 

See whether you like it.

 

cytan


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#94 Psittacula

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Posted 08 April 2018 - 07:36 AM

Hi cytan,

I'd like to make a pull request for an update of Japanese translation.

 

Satoru



#95 cytan299

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Posted 08 April 2018 - 07:57 AM

Hi cytan,

I'd like to make a pull request for an update of Japanese translation.

 

Satoru

I'll merge it once you are done

 

cytan



#96 cytan299

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Posted 13 April 2018 - 02:10 PM

Another successful reported use of the Tri-Bahtinov on a C14.

 

http://buffaloastron...-April-2018.pdf


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#97 Poochpa

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Posted 14 April 2018 - 12:51 PM

Another successful reported use of the Tri-Bahtinov on a C14.

 

http://buffaloastron...-April-2018.pdf

My club, the Buffalo Astronomical Assoc., had problems collimating it’s C14 for years. I told them about my success using the Tri-Bahtinov mask with my 9.25” and gave them the info and links in this thread so they could make and use a mask for the 14”.  Thanks again to you and Satoru from me and on behalf of the club!

Mike


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#98 cytan299

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Posted 14 April 2018 - 02:23 PM

My club, the Buffalo Astronomical Assoc., had problems collimating it’s C14 for years. I told them about my success using the Tri-Bahtinov mask with my 9.25” and gave them the info and links in this thread so they could make and use a mask for the 14”.  Thanks again to you and Satoru from me and on behalf of the club!

Mike

I'm really glad that it worked out! In the article, it says that the mask came from ADM. Is it from ADM accessories? 

 

cytan


Edited by cytan299, 14 April 2018 - 02:23 PM.


#99 Poochpa

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Posted 14 April 2018 - 03:12 PM

I'm really glad that it worked out! In the article, it says that the mask came from ADM. Is it from ADM accessories? 

 

cytan

Yes, the owner of ADM is a member of the Buffalo Astro Assn. He made the mask out of fibreboard solely as a favor to the club.


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#100 Psittacula

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Posted 15 April 2018 - 11:22 AM

I have found out that further reports are published.

 

Satoru


Edited by Psittacula, 15 April 2018 - 11:28 AM.

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