Quote:
Originally Posted by Waxing_Gibbous
Why only slower refractors ?  |
Because these things aren't compact - they consume a fair chunk of focal length. The other reason is that some - and the unihex is an example - use a prism instead of a mirror - the prism adds spherical aberration. In a slow f/15 refractor this didn't matter but in an f/7 or faster scope it's intolerable.