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The following modelling results may possibly be of some use.
314
1.14 pixels/starFWHM in 2 arcsec seeing (heavily undersampled)
ideal broadband sub is 3 minutes under fairly dark sky
420
1.68 pixels/FWHM (undersampled)
ideal sub is about 7 minutes
takes more than twice as long as the 314 to get to a given SNR
As Terry says, a larger scope would be useful, but to image galaxies with the 80mm, the 420 seems to me to be by far the best choice - not much point in getting a galaxy image in half the time if it ends up too small to see.
Re seeing, "good" around here means about 2.5 arcsec. It occasionally drops below 2, but not often - and it can quite happily go over 5.
regards ray
edit: one other thing that you might consider is that, if you ever decide to upgrade scopes, the 314 would be suitable for a small SCT, RC or larger Newtonian, whereas the 420 is best with scopes up to about 1m fl and you would be limited to refractors or fast Newtonians.
Last edited by Shiraz; 06-07-2014 at 07:07 PM.
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