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For visual work, the extra focal length and aperture of the 100 wont make a great deal of difference... A lot of users on these forums have taken images of the moon through ED80. and some are exceptionally good.
There is actually one galaxy that you would be able to image with the 80, but not in its entirety with the 100mm.. M31 - The andromeda galaxy. a 900mm focal length is in fact too long to fit M31 into the field of view, where as the 80mm will squeeze it all in with the camera in the correct orientation.
You'll find planetary imaging with a refractor will provide less pleasing results than with a similarly priced newtonian reflector. Planetary imaging success hinges on a few things, some you can control, some you can not... The ones you can are focal length, and Aperture. I have an 8" with a 5x powermate, giving 200mm of aperture, and a 6000mm focal length. I am upgrading because both aperture and focal length are somewhat insufficient.... where as I use a 90mm refractor with a 600mm focal length for deep sky imaging...
Take a look through the imaging forums... The shorter your focal length, the easier it will be to start imaging... 900mm focal lengths unguided will require a very accurate polar alignment to take images. ~500-600 will be more tolerant to slight inaccuracies.
The larger aperture wont give you more resolution as such.. it will give you bigger image scale through its longer focal length, but as previously mentioned, that comes at the cost of it being more susceptible to polar alignment inaccuracy based errors...
As far as an "all rounder scope.." yes.. its difficult...
For visual observing, you want 3 things.. Aperture, Aperture and a bit of Aperture! 12" Dobsonian reflectors are very popular among observers due to their relative low cost, and massive light gathering capability.
Planetary imaging requires decent aperture with best images coming out of 8" and up scopes... The best images I've personally seen coming from a 14".. and also a long focal length. Its not uncommon to see people planetary imaging with focal lengths of above 11,000mm, and up to 15,000mm depending on the aperture and seeing conditions...
Deep sky imaging.. well... there tends to be no set rules... scopes range from 80mm refractors through to 12" reflectors... If anything seems to be the same throughout, Fast focal ratio's are seen as better.... the faster the scope, the shorter the exposure times need to be.. Ie. an F/5 scope will require half the exposure time of an F/10 scope on the same object. (all things being equal that is)
Hopefully people with more knowledge on the matter find their way in here to fill in anything that I've missed....
Hope I've helped...
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