SPC900 & BAHTINOV MASK

[Third rock]

Hi is it possible to use the mask with a webcam in sharpcap for planetary imaging? Kind regards

[Kbramley]

I use one on mine for Planets but obviously only on a bright star near the Planet, then once focussed I slew to the Planet. I do find though the 3 line pattern is a lot more skewed (the central line does not appear perfectly horizontal) with the webcam, not sure whether this is teling me my collimation is off or the webcam is not properly aligned. Always looks spot on with the 450D though.

HTH

Keith

[Cornelius Varley]

Bahtinov masks work with point source lights (ie stars) so wont work on planets. You could try a Hartman mask Hartmann mask template generator - Billyard Ink.

Peter

[Third rock]

Hmm maybe I'll try one of them. I think I need one I just can't focus on mars. Thanks

[pel]

I achieved perfect focus using a Bahtinov mask to focus a DSLR on Venus. Does that make sense :-) ?

[Third rock]

Venus is a lot brighter than the other planets so maybe that's why you got focus, and you were using a DSLR. That's my theory haha But I don't really no what I'm talking about :-)

[Viv]

I used Venus this year as well, for focusing.

It's worked ok.

[JamesF]

Using the Bahtinov mast with a webcam should work, though I found it quite hard myself once I'd got a 2.5x barlow and extension in the optical train and now tend to do it by eye.

That was trying to use a star for focusing. I've never tried using a planet and was of the opinion it wouldn't work because, as Peter said, I was sure a point source was required. Enough people have now claimed to use planets directly that I'm wondering if its true. My gut feeling is that in theory it only works with a point source, but perhaps in some situations a diffuse source only a handful of arcseconds wide might well have a margin of error too small to affect the outcome. I have done no mathematical calculations to check the idea; it's just the first possible explanation that occurred to me.

James

[Spikey]

Venus is pretty small and bright so it might be OK enough to see the difraction pattern. Easier to focus on a star and then slew back to target.