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One-size-fits-all Bahtinov mask for SCT (5-12 inch)

accessories catadioptric
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#1 Class-M-Planet

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Posted 27 January 2021 - 01:49 AM

Greetings,

 

I am looking to buy a one-size-fits-all Bahtinov mask that would fit SCTs ranging from 5-12 inches, but I couldn't find one anywhere for purchase.  Is there simply no demand for it or physically too awkward?  I am kind of leaning towards a DIY solution of buying the biggest Bahtinov I can find (12 inch with no center hole) and simply sticking three nylon screws into 3 different slits to adjust for different OTA sizes.  Anyone tried this before?  Can the center of the Bahtinov mask be slightly off from the center of the OTA?

 

Thank you so much and clear skies~~


Edited by Class-M-Planet, 27 January 2021 - 01:50 AM.


#2 luxo II

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Posted 27 January 2021 - 02:00 AM

The strength of the diffraction pattern produced by these masks is a function of the linear length of the edges of the bars within the aperture of the scope. 

 

If you use a mask designed for a 12" but place it over a 5", this will have only 40% of the number of bars (and 40% the edge length) of a properly scaled mask to suit a 5", and the resulting diffraction pattern harder to see. It would work, but the pattern will be hard to see in a 5".

 

This is why most use would a mask scaled to suit the scope aperture.


Edited by luxo II, 27 January 2021 - 02:01 AM.

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#3 Class-M-Planet

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Posted 28 January 2021 - 04:43 AM

Thank you for your answer.  I was suspecting that limitations might be spacing/number of bars etc.  I was looking through the internet and saw that the Bahtinov factor needs to be optimally around 150+.  If this is true, and if I were to custom make my mask, I can make the spacing consistent with a 5 inch mask (thinner slit length and more bars) but much longer to fit a 12 inch tube.  For the 12 inch, then the Bahtinov factor might become too large.  I wonder then if this will still work on the 12 inch OTA.  I haven't seen so far that too big of a Bahtinov factor will create problems.  Thank you again in advance!



#4 peta62

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Posted 28 January 2021 - 05:02 AM

Yes, but number of bars can be changed by the Bartinov Factor. I think it would not be such a problem to have more on larger ones, at least worth a try and decide, whether having one for all outweights it.


Edited by peta62, 28 January 2021 - 05:03 AM.


#5 luxo II

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Posted 28 January 2021 - 08:51 PM

Well, try it and see, would be interesting to know for sure.

#6 Class-M-Planet

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Posted 29 January 2021 - 01:33 PM

It may cost more to print and design than buying separate masks, but if I can make a quality one, it might be worth it just for the convenience.  It maybe awhile till I get around to make one and test one.  Just wanted some opinions to ascertain if I am going in the wrong direction.  Thank you so much.



#7 peta62

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Posted 29 January 2021 - 05:25 PM

You know design is free here https://satakagi.git...s/Bahtinov.html ? Just test it before printing, I have seen some thread here about loosing correct size during file format conversion. I am sorry I cannot write more, I am not familiar with 3D printers.



#8 Class-M-Planet

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Posted 31 January 2021 - 03:20 PM

Thank you for the link.  I'll give it a try and calculate what B factor I need for the 12 inch if I were to use the same config as the 5 inch.




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