Well, you have to compare apples with apples.
It isn't fair to compare a $500 10" newtonian with a $10K 127mm triplet apo.
Maybe a comparison should be made between the $500 dob and the 70mm Walmart refractor for fairness.
And you aren't going to find anyone with a 10" triplet apo.
The problem usually is that you aren't going to find equivalent sizes because few people have triplets larger than 5", or newtonians smaller than
8". So the larger scope will have a thermal disadvantage right out of the gate.
The thermal problems can be overcome, but I viewed with someone the other night with a 14" scope with no fans.
Needless to say, his star images showed a lot of heat-related issues.
Then there's collimation, and that is a hard one to overcome--the refractor may need it once in a blue moon, while the reflector needs it every time the scope is set up.
Without that, the star image quality is compromised.
Then there is the nature of the atmosphere, which affects larger scopes more than smaller scopes. What is good seeing for a 4" is not the
same as good seeing for a 14". Larger scopes need steadier air. The 12" Zeiss refractor here in LA at the Griffith Planetarium usually has really
poor image quality because of the air. In perfect conditions, it's magnificent. That doesn't occur often.
And a newtonian will typically need a coma corrector to even get its star images in the ballpark of the refractor.
Then there is optimizing the scope for contrast--something almost always done in the refractor with dewshield, light baffles and star diagonal.
Reflectors can be equally well-designed for contrast, but seldom are.
When everything comes together for either type of scope, the results can be amazing. But the reflector, being larger, will always have the advantage of resolution.
It is possible to have a larger reflector that yields refractor-like images. It's just that most people don't want to pay for that.
Edited by Starman1, 15 April 2018 - 09:52 AM.