Quote:
Originally Posted by glend
I realise the long focal length imaging at f8 does require more time, but honestly the focal length of the RC08 (at around 1600mm) is only 20% longer than my 10" f5 newt (@ 1250mm). The 190mm Mak-newt does have an advantage at f5.3 and 1000mm fl.
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your f8 system is only 1/3 as sensitive as your f5 system (the ratio of the square of the FNo) - that is a huge difference and way more than 20%. You could maybe consider subs that are 3-4x as long as those that you used with the Newtonian and total exposure time that is 3x as long.
The MN system will be slightly less sensitive than the Newtonian.