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Another way to reduce noise significantly is to create a dark frame. A dark frame is a picture that you take when the lens of the camera has the cap on. No light gets in but the noise is still there. You in effect take a picture of the noise. You then use computer software to subtract the noise layer from your photos.

This works because not all aspects of noise are random. For example, some pixels in the camera's CMOS/CCD chip are always noisier than others. Also there is a certain predictable "average" level of noise for each pixel (sort of like how temperature is an average measure of the random movement of molecules).

Armed with your dark frame you then use the computer software to subtract it from your photos. You'll be amazed at how well this works. Fuzzy noisy photos clear up like magic.


To simplify it a Flat is a picture that you take of a moderately, and evenly, lit featureless wall or twilight sky. The purpose of it is to show up the optical defects in your equipment. For example, dust specs, vignetting and even differences in pixel sensitivity are all visible in a Flat.

You then use the Flat in the software to even out these irregularities and improve the overall image. Using a Flat is, IMHO, less important than getting your darks working.

Darks are I believe critical.

I haven't yet graduated to creating images of a quality where I feel it necessary to invest in taking flats - maybe one day soon...:o) I hope.

The big thing to remember with flats is that they are only useful if the flat is taken with the EXACT same optical setup as your lights. If you rotate the lens, or the camera in the telescope, or if you change other things in the optical path you'll have to take another flat to match.


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