587 replies to this topic

[Endymion]

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

 

[cytan299]

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.

[Endymion]

Thanks cytan!

[Brain&Force]

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:

 

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.

 

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

[Whichwayisnorth]

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

[cytan299]

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

[teashea]

Hi,

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

IMG_0086.jpg

 

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

as_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

collimated.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

[Psittacula]

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/

[ontherivet]

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

 

Thanks,

Don

[Psittacula]

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

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

[Whichwayisnorth]

Doesn't this link work?

 

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

 

cytan

Yes sorry that does work but looking for a ready to download/print .stl for my 3d printer.  Asking if people have one they could share.  Thanks

[Psittacula]

Yes sorry that does work but looking for a ready to download/print .stl for my 3d printer.  Asking if people have one they could share.  Thanks

I think you can convert from svg to stl. The following content may be helpful.
https://all3dp.com/2...printable-stls/

 

satoru

[Psittacula]

I think you can convert from svg to stl. The following content may be helpful.
https://all3dp.com/2...printable-stls/

 

satoru

The tri-bahtinov mask generator will generate outline data, i.e. data for a laser cutter or cutting machine. However, the stl files required for 3D printers etc., require filled data, i.e. polygon data.

Using inkscape, you can polygonize the outline data. This is a bit of a complicated process, but it is easy to do.

 

I have placed a brief description and instructional video here.

https://satakagi.git...WebApps/#tomake

[Borodog]

Forgive me if this has been covered somewhere in this very long thread already, but can someone comment on the accuracy of collimation using the tri-Bahtinov mask? As in, has anyone collimated using the mask and then double checked with a tool like MetaGuide?

[MarMax]

Forgive me if this has been covered somewhere in this very long thread already, but can someone comment on the accuracy of collimation using the tri-Bahtinov mask? As in, has anyone collimated using the mask and then double checked with a tool like MetaGuide?

I can provide what I've experienced so far with the C11 in my 3/5 conditions (seeing and transparency). I've not actually had a 4/5 night yet where I tested the Tri-B mask. I have a Buckeyestargazer Tri-B mask and find that with Polaris it can be a bit hard to see the spikes. Both visually and in attempts to video with the 464 camera. It's still a work in progress.

 

I've found the mask to be very helpful to get to the 90% point but that last little bit is tough to discern when things are wobbling all over the place. I think the Duncan mask is a little bit better from the 90-95% point in 3/5 conditions. This is about where I'm at now.

 

I've not tried MetaGuide as you have because there is no DirectShow driver yet for the NCII 464. But taking video of Polaris in-focus seems to be the next step IMO to improve from the 90-95% point. MetaGuide live stacking should be the ultimate tool if it works.

 

The other thing I need to try with the Tri-B mask is a brighter star. In theory the Tri-B mask should work to get to 98% collimation. And I wonder what you'd get with a Tri-B mask and Metaguide. I don't think you can solve the "too tight" collimation screw problem using the Tri-B mask but you should be able to get best collimation. IMO you need a MetaGuide or other video of the in-focus star to see if you are deforming the secondary.

[Borodog]

I've tried MetaGuide repeatedly. I know it's probably just the seeing, but so far I am not having much luck. I know my collimation is close but no cigar, but I haven't been able to get much out of MG. It's been frustrating. Hence the want to move to something else, like the TBM.

[archer1960]

I can provide what I've experienced so far with the C11 in my 3/5 conditions (seeing and transparency). I've not actually had a 4/5 night yet where I tested the Tri-B mask. I have a Buckeyestargazer Tri-B mask and find that with Polaris it can be a bit hard to see the spikes. Both visually and in attempts to video with the 464 camera. It's still a work in progress.

 

I've found the mask to be very helpful to get to the 90% point but that last little bit is tough to discern when things are wobbling all over the place. I think the Duncan mask is a little bit better from the 90-95% point in 3/5 conditions. This is about where I'm at now.

 

I've not tried MetaGuide as you have because there is no DirectShow driver yet for the NCII 464. But taking video of Polaris in-focus seems to be the next step IMO to improve from the 90-95% point. MetaGuide live stacking should be the ultimate tool if it works.

 

The other thing I need to try with the Tri-B mask is a brighter star. In theory the Tri-B mask should work to get to 98% collimation. And I wonder what you'd get with a Tri-B mask and Metaguide. I don't think you can solve the "too tight" collimation screw problem using the Tri-B mask but you should be able to get best collimation. IMO you need a MetaGuide or other video of the in-focus star to see if you are deforming the secondary.

Try using a star that is more directly overhead than polaris. It probably won't wobble as much due to the seeing.

[GDN]

A couple of questions:

 

1)  Has anyone tried to make a mask for focusing a Meade 16-inch SCT?

2)  Is there a commercially made Bahtinov mask for a Meade 16-inch SCT?

3)  Where and / or who(m) can print a mask this size?  And how thick?

[Psittacula]

2)  Is there a commercially made Bahtinov mask for a Meade 16-inch SCT?

It looks like buckeyestargazer is accepting orders.

https://buckeyestarg...TriBahtinov.php

[fractal]

Hello to all!
I’m amateur astronomer writing from the middle of the italian adriatic coast.
I’m using fairpoint bahtinov mask since his invention on my Meade LXD75 SC8”.
For collimation, I still using a hartmann mask with three triangular holes.

I’ve readed all the replies to this post and other post talking of this.
I’ve made my own mask but the hand cutting was to bad that the spikes are not clear and in fact is inusable.

I would send it to a laser cutting store but before make this investments some questions rises to me:
1. In the original bahtinov mask the angled slits have 20° instead of 10° of the tribahtinov. Which angle is better?
2. Trasparent is better than opaque?
3. If yes, which material is better between acrylic (plexiglass) and polycarbonate (lexan) and how much thick the sheet (my fairpoint astro opaque bahtinov mask is 2mm thickness)?
4. Engraving is better than cutting (like WO models)? I’ve noticed that some WO mask are made of combination of two technics.

I still don’t understand the relation between the widht of stem and slit and how this can influence the final image looking through the telescope.
If the stem can be the minimum, like with engraving instead of laser cutting, many narrow slits is better than few broad slits?

Thank’s in advance for any replies.
Alex

[cytan299]

Hello to all!
I’m amateur astronomer writing from the middle of the italian adriatic coast.
I’m using fairpoint bahtinov mask since his invention on my Meade LXD75 SC8”.
For collimation, I still using a hartmann mask with three triangular holes.

I’ve readed all the replies to this post and other post talking of this.
I’ve made my own mask but the hand cutting was to bad that the spikes are not clear and in fact is inusable.

I would send it to a laser cutting store but before make this investments some questions rises to me:
1. In the original bahtinov mask the angled slits have 20° instead of 10° of the tribahtinov. Which angle is better?
2. Trasparent is better than opaque?
3. If yes, which material is better between acrylic (plexiglass) and polycarbonate (lexan) and how much thick the sheet (my fairpoint astro opaque bahtinov mask is 2mm thickness)?
4. Engraving is better than cutting (like WO models)? I’ve noticed that some WO mask are made of combination of two technics.

I still don’t understand the relation between the widht of stem and slit and how this can influence the final image looking through the telescope.
If the stem can be the minimum, like with engraving instead of laser cutting, many narrow slits is better than few broad slits?

Thank’s in advance for any replies.
Alex

IMO, the angle is really not that critical. The more slits you have, the sharper the diffraction spikes. The width of the stem is really for strength, so choose a width that you're comfortable with. Obviously, the more slits, the more fragile the mask is going to be as well. So, it is a balance.

 

My original masks were made from acrylic which is quite fragile because of the slits. Now I use 3 mm thick MDF with the laser cutting service from Ponoko. MDF is a lot stronger than acrylic.

 

I don't really understand why transparent masks would actually work well. Light is going through a transparent material that has no guarantee flatness is, IMO, not a good idea. So I'd use a non-transparent material and use real slits.

 

As usual YMMV

 

cytan

Edited by cytan299, 09 November 2021 - 09:08 AM.

[fractal]

Hi Cytan, thank’s for your kindly answer, I will follow your suggestion.

[Dennis_Oz]

Here is my 1st light with the Farpoint Tri-Bahtinov Mask for Celestron 9.25 SCT.

 

I used this on my new C9.25 EdgeHD with a TeleVue x2.0 PowerMate and ASI 174 MM camera at an efl of 4700mm at F20.

 

The seeing was around 4-5/10.

 

Cheers

 

Dennis

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[Borodog]

Sorry if this question has already been asked somewhere, but is there a reason the tri-Bahtinov  mask would not also work for collimating a Dobsonian? It also has 3 collimation screws, no?

[cytan299]

Sorry if this question has already been asked somewhere, but is there a reason the tri-Bahtinov  mask would not also work for collimating a Dobsonian? It also has 3 collimation screws, no?

I would think the Tri-Bahtinov will work in a Dobsonian as well because it works on a Newtonian:

 

https://www.cloudyni...sing/?p=8026516

 

Please post if it works or doesn’t.

 

cytan