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Bahtinov Mask


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Does anyone own a Bahtinov Mask? I'm thinking of getting one for my SW 200 dob because I'm always fiddling with the focus thinking I can get slightly better focus (I think it's a bit of OCD lol).

Also it should come in handy when I'm doing a bit of astro photography cos I find it hard to focus on a planet on the laptop screen.

David.

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Bahtinov masks are excellent for checking and achieving focus. You can easily make one yourself with a template, stiff plastic and a craft knife. Once you have one, Simply target the scope on a bright star and adjust your focus until you have the central diffusion spikes in the middle. You could try this mask generator. http://astrojargon.net/MaskGenerator.aspx

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If you're lazy like me, you can get them on ebay for almost any telescope model. I bought mine for the 200P from Keith Morris Engraving, loads seem to use his masks as well. They are excellent. :)

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I bought mine for the 200P from Keith Morris Engraving, loads seem to use his masks as well. They are excellent. :)

Couldn't agree more - I too purchased mine from Keith - excellent product. and excellent service

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If you want to try something quick, then cut out an alternative Y mask from a black plastic document cover or the like, the arms of the Y and stem about 8mm wide, but you can experiment with the width to see if it gives you a better focusing image / diffraction pattern, could save you some money :)

John.

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10 minutes to make and 30 seconds to use.

I'm going to get a 10:1 focuser, but don't have one atm.

Until I do, the mask is my bestie. What I used to think was in focus was not. Once it was.........

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  • 2 weeks later...

Quick question: can you use a Bahtinov Mask that was designed for one type of scope with another scope? I have a mask that I got for my previous scope an 8" Meade SCT F10 and have been using it with my 8" RC F8 - it seems to work OK but wondered if a mask designed for use with the RC would provide a different focus position?

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A mask only provides diffraction spikes. Your Airy disc is a diffraction of the open aperture of your scope, where a wave front of light strikes the rim of the OTA. The widths and spacings of the mask may make some difference in the spike patterns in the two scopes because of the different focal length, but as they are both 200mm scopes I would have thought this would make little difference to the focus position. If it is working for you, perhaps you may be able to check this point yourself at some time :)

John.

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A mask only provides diffraction spikes. Your Airy disc is a diffraction of the open aperture of your scope, where a wave front of light strikes the rim of the OTA. The widths and spacings of the mask may make some difference in the spike patterns in the two scopes because of the different focal length, but as they are both 200mm scopes I would have thought this would make little difference to the focus position. If it is working for you, perhaps you may be able to check this point yourself at some time :)

John.

OK - thanks John.

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  • 2 weeks later...

Another vote for Keith Morris - I ordered masks for both my scopes from him. Good quality and speedy service. And as Strath says - it helps callibrate your eyes :D I now have much more confidence in my visual focussing.

Edited by SeedyF
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  • 3 weeks later...

I used my new Bahtinov mask for the 1st time last night and I'm very impressed with it! I focused on a bright star (Vega) and saw the very distinctive defraction spikes, it took just a few seconds to get perfect focus :)

But here's a question - when you have set your focus using the Bahtinov mask will this be the perfect focus to use on the moon? (because the moon is so much closer to us than the distant stars)

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But here's a question - when you have set your focus using the Bahtinov mask will this be the perfect focus to use on the moon? (because the moon is so much closer to us than the distant stars)

Yes it will be fine - the distances involved should not make that much of a difference

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