It depends on what type of image you want to produce.
F8 200mm = 1600mm focal length = more closeup more highly magnified than F5 200mm = 1000mm focal length.
A common and very useful focal length for imaging is 1200mm.
F5 is a preferable focal ratio than F8. Not that there is anything wrong with F8 but it is more demanding on accuracy of tracking and will give more closeup views of objects. Maybe you prefer widerfield images. F5 will also get a bright image faster - more than twice as fast as F8 for the same aperture. So that may be good for your imaging requirements - perhaps you live in area where clouds often interrupt imaging. Well F5 is more productive than F8.
Collimation requirements for both will be important but a Newt is easier to collimate than an RC.
Then again F5 200mm will not capture too many galaxies whereas F8 at 200 will get quite a few.
So different strokes for different folks. No right or wrong about it but what type of image would you like to produce is the primary question coupled with what environment are you imaging from. Also what size camera chip as the bigger the chip the more you need a large corrected field which only some configurations of scopes can provide.
For a DSLR I imagine you are in safe territory with either scopes.
Also longer focal length often means a longer tube which is more wind affected.
If you travel to a dark site to image then F5 200mm would be far more productive and less likely to result in a nonproductive trip is clouds are hanging around. F8 200mm would require clearer less windy conditions to be productive but you could image a nice galaxy shot with it or a closeup of some DSO.
For less experienced imagers shorter focal length is always the way to go as the longer the focal length the more accurate everything has to be and the longer the exposure time to get a decent image.
Personally I think you would find most people would prefer an image taken from an F5 200 Newt well setup to a F8 200 RC. You'd get more positive feedback on most images (not all).
That is my experience anyway.
Greg
Quote:
Originally Posted by toryglen-boy
i dont know much about the RC design, or the pros and cons to it. Would this better than an F5 200mm reflector for DSO imaging?
thanks
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