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Also, Pat - see the darkness around the edge of the image, surrounding a brighter central circle? This is "vignetting", a consequence of the optics of your telescope.
You can eliminate this by taking "flats" - short exposures (maybe around 1/50s given your setup) of a uniform light surface - a lightbox, or a white cloth stretched across the scope, or the twilight/dawn sky. These have to be taken before you touch the scope/camera setup - everything has to be *exactly* the same as when you took your lights.
It's too late to get these now for your M83 image. But you can crop the dark edges out of the image pretty well.
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