Prism vs Mirror Diagonals

Hi all,

Just wondering which of these are the best as far as seeing quality goes. I've had a lot of good luck with the prism diagonals and the mirrors that I have looked through weren't the best of quality. I was just wondering if there are any hard facts as to which is better or if it's simply a matter of opinion?

Thanks

Well, even if they are perfectly made, prisms add chromatic and spherical aberration. The faster the scope, the more aberration added. Few recommend 1.25" prism diagonals on anything faster than about f/6 and most would probably draw the line more conservatively at about f/8 or even slower. In any case, it's essential to get a high quality diagonal whatever its design.

FYI, nobody seems to recommend 2" prism diagonals under virtually any circumstances.
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Mike