Hi Ric. The longer the focal length of your scope the shorter your exposure time until field rotation comes into effect. Eric is working off an EQ mount so he doesn't have that problem so his exposure times are related to how long to burn out the stars (sigma clipping) and how much noise can be dealt with etc. Another thing to take into consideration is chip size. A Canon 300D will show rotation near its outer edges in around 30 - 45 sec at 2000mm fl but with the DSI with it's smaller chip you will have a bit more latitude. At a rough guess I'd say you should be right for exposures of 60 sec. You will be able to get a lot of obects that will come in easily in that time frame with stacking multiple images.
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