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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.



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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.


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