Quote:
Originally Posted by bluesilver
Thanks for the reply, appreciated.
I could be thinking wrong here, but maybe an aperture mask on the 16 inch dobsonian could help dull out the brightness while still having the large aperture?
I could be thinking it all wrong here though.
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Why buy a bigger 'scope only to reduce its aperture? Once you put an aperture mask on that is then your aperture. The focal length remains the same but focal ratio changes. E.g. A 16" f4.5 would become a 4.5" f16.
The exit pupil will be reduced for the same magnification with an aperture mask in place so images will be less bright and this will help but the same can be achieved with your 10" at full aperture given the right magnification. You lose resolution too with your aperture mask but given a good mirror, good seeing and good collimation you should be able to see Ganymede's disk easily at 4.5" but it will resolve more easily at 10" or 16" provided conditions are right.