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Originally Posted by Rastis
Please answer true or false and why to the following statement.
A 4 inch refractor will show more contrast and I personally think the images are sharper then a 8 inch DOB.
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That depends on a large number of variables which you haven't specified in your question.
A bad 8" dob will easily outperform a cheap fast achromatic refractor on EVERYTHING except low power wide field views.
An 8" dob against a good 4" refractor ?
Thats marginally closer, it depends a lot on who built the dob, how good the mirror in it is, how well its baffled, how well its collimated, if its properly cooled etc etc. In addition a slow dob eg F8 or slower will perform even better as a planetary scope due to a smaller secondary mirror.
Lets assume however a good 8"/F6 dob and a good 4" flourite doublet.
The 4" APO will show nicer stars, thats about it. The 8" dob will show infinitely more detail in moments of good seeing than the refactor. The dob will also go a lot deeper. IMO "a good" 8" dob will walk all over a 4" APO in just about everything. But then thats only my opinion, but I have been there and tried it. Also tried a 4" Flourite APO against a 10" dob and the 10" blows the 4" away by a bigger margin.
CS-John B