6 replies to this topic

[Frank2]

I have Bahtinove masks for my 16" Newt and 120mm frac. The Newt acts as expected with a cross and bisecting line that passes through the X as it focuses. The frac however shows 3 dots in a line that go in and out of focus. If I put a very bright star in the field I can barely make out a bisecting line and faint X pattern. The small masks looks like a smaller version of the big mask. These are the only Bahtinov masks I have ever used. So what's the deal? All masks don't work equally well, or the bigger the scope the better they work, does focal ratio make a difference? The mask on the 120mm frac is pretty useless. Have others found this to be true also?

[Tapio]

Sounds like your frac Bahtinov mask is not optimal.

I use masks with both with my C8 and 80mm frac (and even smaller camera optics) and they work just fine - granted only with camera.

[Darkblade48]

Probably just your Newt being better at collecting light than the smaller refractor.

 

I use a Bahtinov for focusing (albeit for photography), and notice I need longer exposures on smaller diameter scopes. Unfortunately, this trick won't work since you are (presumably) using it for visual

[Frank2]

Sounds like your frac Bahtinov mask is not optimal.
I use masks with both with my C8 and 80mm frac (and even smaller camera optics) and they work just fine - granted only with camera.

Interesting. So just because it looks like a Bahtinov mask doesn't mean it really is a Bahtinov mask. The one with the thicker border is the one for the frac, the other is the one for the 16".

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[Tapio]

Maybe my Bahtinov for frac has thinner bars (=let more light)?

 

There are Bahtinov mask generators online, and with them you can print your own (with 3D printer).

 

 

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[Frank2]

Seems like thinner and more lines gives better results. I'm going shopping for a better mask armed with this new information.

[luxo II]

I used an online generator to create the drawing as SVG then had sone laser-cut in acrylic, worked fine. … and yes more slits are better than fewer slits.