Gary Parkerson
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Eyepieces - the very least you need.
in Getting Started General Help and Advice
Posted
Excellent original post and thread!
There's little I can add but to share what eyepieces I actually use after more than a decade of total immersion in the study of astro equipment. Put simply, the few eyepieces that I can't do without are those that produce exit pupils of 5mm, 2mm, and 1mm, regardless of scope. Of those, whichever eyepiece produces an exit pupil of ~2mm is going to see the most use. And if I were young again, I'd want an eyepiece that yields an exit pupil of as much as 7mm.
Few of us possess eyes with no inherent aberrations and large exit pupils tend to exaggerate aberrations of the eye - especially astigmatism. Similarly, many of us suffer to some extent from eye floaters and small exit pupils tend to floresce the things to the point of distraction. As do many, I therefore find the most comfortable range being exit pupils of 1 to 4mm in diameter, with 2mm being the most common sweet spot.
The premium wide-field eyepieces are fantastic and well worth the rather significant investment, but a well constructed Plossl is competent and forgiving, especially at focal ratios of f/6 and greater. Having tasted the ultra-wide experience, I'd find it hard to go back to a 50-degree AFOV, but when teasing fine detail from all but the most extended objects, few designs significantly exceed the image fidelity produced by a Plossl with lens elements of highest polish and premium coatings.
But regardless of eyepiece brand or design, 3 eyepieces and a 1.5x Barlow are generally all that I actually use during any given night and it's a rare night that finds me choosing one that produces an exit pupil smaller than 1mm with whatever scope is at hand. If I need more magnification, I just have to move to a scope of sufficient aperture to produce that magnification with an exit pupil of greater than 1mm. Your age-affected eye-pupil diameter, degree of eye astigmatism, and eye-floater count will vary, but you're still likely to find that an exit pupil of ~2mm is most comfortable for general viewing.
Hope this helps.
Gary