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The ST80 is an achromat type refractor, and has significant chromatic aberation (CA). This results in an offset or fringing of some colours. So yes a scope like an ED80, which gives truer colour rendition will appear sharper as the colors are aligned so to speak.
Secondly, an AZ mount is ok for very short exposures of bright objects like the Moon, but for long exposure photos you will eventually need a tracking mount, like an equatorial (EQ).
Stacking and processing are another aspect of astrophotography but i would suggest you concentrate on getting some good well focused single exposures before you get into the complexities. Focusing is important, and if your camera has Liveview this helps, but a focus mask guves you a prismatic pattern that allows you to get it perfect.
Have fun.
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