Quote:
Originally Posted by multiweb
Visual or imaging in effect what you are doing is barlowing x2 an F/5 if you double the FL.
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No, not quite, only as far as the final magnification is concerned.
The f/10 scope will generally be more pleasing to look through, most aberrations will be diminished compared to the f/5 one, and it will have better apparent contrast due to the darker sky background.
IMO fast scopes are "only" good for astrophotography, or when you can't handle the longer OTA size for some reason (large OTAs can be an issue in windy conditions).
Cheers
Steffen.