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StuartJPP

Home-made Bahtinov vs. Y-mask

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I made a Bahtinov mask out of matt black foam board a couple of years ago and since I still had a couple of boards left I thought I'd try and make a Y-mask to compare the results and the ease of producing one. Foam board is not ideal as it is too thick and keeping the cuts straight is difficult, so I would suggest some stiff cardboard instead or some acrylic/plexiglass.

I made an artificial star by using a bright LED torch and drilled a 0.3mm hole into a black plastic cover, worked quite well.

Both images were taken seconds apart with exactly the same exposure and focus settings. Although the Y-mask is brighter (as can be seen by the background), the diffraction spikes are pretty much the same and are probably longer with the Bahtinov. The lines on the Y-mask are cleaner/sharper, probably because there are less edges that may not be 100% perfect.

Both masks are the pretty much the same size using the recommended thicknesses/width/dimensions for my OTA (well best I could find)...

I actually just prefer using FWHM or HFD for focus...just keeping myself busy on these rubbish nights.

Naturally the Y-mask is much easier and quicker to make.

Bahtinov Mask
MZ0A8087_Bahtinov_Mask.jpg

Y-Mask
MZ0A8086_Y_Mask.jpg

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Nice comparison. I can imagine that edge roughness may be an important quality measure for these masks.

Also interesting to read about the artificial star. At what distance did you put it?

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11 hours ago, wimvb said:

Nice comparison. I can imagine that edge roughness may be an important quality measure for these masks.

Which makes the Y-mask easier to make properly as there are fewer edges to worry about. Would be interesting to compare my home-made one to a proper laser cut mask.

 

11 hours ago, wimvb said:

Also interesting to read about the artificial star. At what distance did you put it?

The artificial star was placed about 8 meters away, purely because it is convenient at that distance. I did try using a piece of fibre optic attached to very bright white LED but since it was about 0.9mm in diameter it was resolving as a disc, hence the 0.3mm hole.

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I am tempted to make the Y mask if it is easier.....the results are very similar indeed. Would you mind putting up a pic of your Y mask? cheers, Andy

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+1 for the Y mask being easier to make.

I tried making a bahtinow a wile back, but failed. The Y mask was a lot easier. I made the Y by cutting it out from a old black dvd case.

Used tape on the 'top' to fix it to a cardboard holder. Everything was then painted with blackboard paint.

Interested in seeing yours too Stuart :)

DSC_0106.JPG

 

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Here's some quick images of the masks side-by-side. The two holes are for the pegs to fit into for keeping it in place on the lens hood.

Just for reference and scale, the lens hood is approximately 150mm in diameter (the lens itself is 125mm).

 

Y_vs_Bahtinov_3.JPG

Y_vs_Bahtinov_1.JPG

Y_vs_Bahtinov_2.JPG

Edited by StuartJPP
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Interesting - looking for some help with DSLR focusing and a Y mask would be easier to make for a camera lens :smile:

Helen

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Thanks Stuart....I am now totally enthused to make a y mask for my 127 mak and also a mini version for my camera lenses ???

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For a camera lens, does the Y need to be any particular width.  i.e. thick or thin Y?

Carole 

 

Edited by carastro

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Hi Carole, for the widths I used the standard recommendation....Can't remember where the original link is but it was fairly easy to find at the time.

If I can find the link again I will post it...It was under a thread here on SGL, something along the lines of Lord Y Mask.

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Thanks Stuart, I will also try to copy your artificial star idea, so I don't need to wait for a clear sky to test it out.

Carole 

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I think I have found the thread you refer to, thanks.

Carole 

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On 7 December 2016 at 23:00, Helen said:

Interesting - looking for some help with DSLR focusing and a Y mask would be easier to make for a camera lens :smile:

Helen

Would a Hartmann mask using 3 holes be easiey to make

i got a 100 MM. Bahtinov mask to try on my camera lens but as usual the sky's aren't playing ball

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Well I had a try to get focus last night using both a Y mask and a small bahtinov mask made for my WOZS71.

Hopeless results - the bahtinov mask just showed a pattern of the bahtinov spokes on the star itself, and this is what i got with with my 28 - 200 zoom lens at roughly 100mm with the Y mask:

(Mosaic of different effects), as you can see there is shocking LP in my location.

I tried 2 different Y masks as one of them I have used before and it worked OKish. 

Must have spent over an hour trying to get focus. 

Any thoughts?

Mosaic of results.jpg

Edited by carastro

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OK, I am going to try a Hartmann's mask now and see if that works any better.

maske2.jpg&f=1

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For anybody interested, I found a site where you can download printable Bahtinov Masks.

I printed one for my telescope out on clear velum stock, then mounted it in a slip over collar of PVC.

It worked OK, and I still have it. I did get a plastic one later on, which I use currently.

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Made a couple myself a few months ago to check the colimnation of a pair of 15*70 Binos, yes they work and if you make them yourself cheap

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On 17/04/2017 at 12:05, gtis said:

Would a Hartmann mask using 3 holes be easiey to make

i got a 100 MM. Bahtinov mask to try on my camera lens but as usual the sky's aren't playing ball

Well finally  tried the  bahtinov mask last night and what a waste of time the photos ended up like carastro's I couldn't even see the star through the camera lens

I was like the spokes where too thick will try a Hartmann mask with just two holes

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I have made three bahtinov masks and all have been successful. I thought the y mask would be a better solution buy after making one for my 130pds all I got was a y shape over the image and no refraction's of the star.

Not sure what went wrong.

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I made one (well, printed it on clear velum stock). I made it for a 100 mm so I would have room for my PVC pipe adapter.

Then I bought one and I thought it worked better. But it was plastic, and it broke a few times. Repaired with CA glue.

Then I bought a metal one that I don't like at all.

I might take the one I do like, and adapt it onto my PVC sleeve, and hopefully have what I'd like to have.... something both usable, and 'Sonny proof'. :icon_biggrin:

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