Quote:
Originally Posted by Profiler
Hello John B
While we are on the topic of Pentax XF series eyepieces do you have any thoughts or information you could share on the merits of the Pentax XF 6.5-19.5mm Zoom eyepiece?
Would you happen to know whether it is any better than the Baader Zoom for example?
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I have never used this eyepiece, and the reports I have read indicate that it is a decent eyepiece but not great. From what I have read its performance deteriorates off axis.
To be honest I dislike zoom eyepieces for astronomy because in most cases the AFOV gets narrower as the focal length is increased. IMO, for all practical purposes it should be the opposite, where the AFOV gets wider as the focal length is increased and the magnification reduced. Further, zoom eyepieces are generally not quite the optical equal of fixed focal length eyepiecs. You need to understand that it is impossible to get a "zoom anything" close to perfection across the entire focal length range, particularly when the range is wide like it is in this particular case, unless you spend an enormous amount of money. That applies to eyepieces, binoculars, camera lenses and riflescopes. A fixed focal length camera lens will "always" outperform a zoom lens near the extremeties of the zoom range. This is the reason the Televue zooms have a very small zoom range. There are the odd good zoom eyepieces, but they are frightfully expensive. The Leica Zoom is exceptional.
http://www.apm-telescopes.net/en/pro...cd962409f1259b
It's also $1,200 landed in Australia.
Cheers,
John B