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I am experiencing a problem with using the histogram feature for faint objects (e.g., Heart Nebula, Calif. Nebula, etc.). My usual techniques if to set exposure so that the peak of my histogram is about 1/3 of the way from the left. For the really faint objects though, especially when using my 200mm f2.8 Canon lens, I'm not getting enough data to work with. It has been suggested that the histogram feature converts the raw data to JPEG before displaying the histogram and that this may lead to a small amount of initial pre-stretching. I don't know if that is true or if it is simply to do with loss of bit-depth as you go from 14 to 8 bits. I do know by checking Astrobin that other people imaging the same objects with the same gear are using significantly more exposure time that my histograms have been leading me too. I'm wondering if the on-camera Canon histogram might be more accurate, albeit more difficult to look at on the telescope. I tried to check this by copying one of my problem lights back into the camera but got an error that I wasn't authorized to do that. I was able to copy it onto the SD chip but when I reinsert it into the camera and press the play button it doesn't show. I know I can check this on a fresh picture in my next observing session but I'd like to resolve it before then.
1. Has anyone else experienced this and, if so, how did you resolve it?
2. Is there a way to look at the image that I copied to the chip and display it on-camera? I'm pretty sure this can be done but don't recall just how.
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