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Originally Posted by Robert_T
Good one Matt.... hmmm maybe I should have a chat with lex on what Pentaxy things he has in the >20mm range  |
Robert,
Let me warn you in advance that the 20mm Pentax XW is not quite to the same high standard as the shorter focal length ones. It suffers minor field curvature and the amount of this, is dependant on the design and F-Ratio of the scope its used in. Looking at two of your scopes a C9.25 and a Tak Mewlon 180. The SCT has a curved focal plane inherent with its design and the Tak is a Dall Kirkham design which is best used for narrow field work as it is. So I doubt that either of these with the 20mm Pentax would be a match made in heaven at the EOF.
On axis, the 20mm Pentax is very sharp, has excellent light transmission and contrast, superior to any other premium widefield on the market IMO, but it is not tack sharp to the EOF due to the field curvature. Its still a very very good eyepiece and light years ahead of the cheap widefields but in the 20mm to 24mm focal length with a 1.25" barrell, there are better options available IMO, if you are looking for top performance across the entire FOV.
What focal length eyepiece are you looking for and do you need long eye-relief ? Do you need a 1.25" eyepiece or is a 2" eyepiece an option ?
CS-John B