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New CCD - questions

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I noticed some stars in the sky so I rushed to try out my new (to me) SXVF-H9. I set up the mount, aligned the GOTO and then put the camera in. I used the SX software to acheive focus and then I took a single 20 second frame. It was rather grainy.

Unfortunately the clouds then came over and that was then end of that. I did take some flat frames, here are 15 that have been run through DSS to stack - again it is rather grainy.

Are these normal - they seem much more grainy than I am used to with my DSLR.



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That looks fine to me. DSLRs only have 8-bit images (I think!?!?!?; 0-255), so the scaling is set that you don't see the noise so much. CCDs have 16-bit images (0-65536) usually, which means you set the scaling much finer, which means you see the noise more easily. It's not that it is noisier (it will be less noisy almost certainly), just that the image scaling lets you see it. For example, in an 8-bit image, the background would probably have either 0 counts, or 1 count (say) so look pretty 'black'. In a 16-bit image, the exactly equivalent background would now go between 0 counts and 256 counts, so there will be much more range and it will look a lot grainier.

That of course means you have better flux resolution in the image, which is a good thing.

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It looked surprisingly clean when I looked at it, but the flats tell a different story! I will definately have to clean it up (and buy a filter wheel plus filters) when I get chance when I get back from the very dark sky site high in the mountains where I will be for a while (that I will not, unfortunately, be taking my telescope to but I might take some binoculars).

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