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Re: The Best Value - A Question Not Answered

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Posted by Chris on February 11, 2001 21:07:34 UTC

There seems to be one or two misplaced generalisations here, and generalisations that many astronomers appear to hold. Nagler is better than plossl? At what? At providing a wider apparent field? Of course. At providing better centre-field characteristics? Not neccessarily. If standards of tolerances are equal at manufacturing stage, then the centre-field characteristics of a properly designed orthoscopic or plossl are about as good as you'll see, (although fans of Tolles eyepieces would disagree). Naglers are quite well corrected for an 82 degree eyepiece, they have to be, there is no point in 82 degrees if you can't use 82 degrees. However, when people often compare planetary images in Naglers vs. classic orthos. or plossls, the reason why some rate Naglers equally at centre-field performance is that Japanese and other Asian orthos. and plossls are not constructed to the standard they could be, even the quality ones. If you get the chance, try a Zeiss Abbe Orthoscopic or a French Clave Plossl.
Widefield gives less eyestrain? Where did you hear this? Field width has no relevance to eyestrain. Squinting through small 4mm or low eye-relief eyepieces is more relevant, although this has more to do with the physical size of the eyelens and fieldlens than width of field.
As to eyepiece makes. I have found from years of experience using all types of designs that the following are worth considering, not in any particular order of merit:
All Televue eyepieces appear to provide high quality images.
Clave plossls.
Takahashi plossls and orthoscopics.
Pentax orthoscopics and wide-field designs.
Japanese orthoscopics including the University Optics labelled versions.
Meade eyepieces are OK, although not (in my opinion) as well corrected as the Televue equivalents.
The Celestron Ultima series (and the similar Parks and Orion Ultrascopic versions). The 30mm is particularly desirable.
Vixen plossls; 26mm, 13mm, 9.5mm, 7.3mm. Still available according to their website.
Nikon eyepieces used on their Fieldscopes. I kid you not! A 1 1/4" adapter will need to be constructed.
All of the above are generally available on the market and will perform well on all astronomical telescope designs, but remember to test them (if you get the opportunity to test some of them together), on centre-field performance (contrast, astigmatism, chromatism, field curvature, and colour bias introduced by the metal coatings on the lenses). Do not judge them according to their width of apparent field. Remember also, that when choosing a long focal length 1 1/4" eyepiece for your ETX 90, try it first, there may be one or two that vignette the image.

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