[Don Pensack]

Originally Posted by Wavytone

Don I disagree. You imply most eyepieces - even the cheap ones are reasonably good. This is simply not true - there are bloody awful ones out there which belong firmly in the trash.

Well, most people don't own Huygens and Ramsden eyepieces, and you will note that i mention the center 50% of the field in my post. The differences are largely in the outer field.

While it is true that something as deceptively simple as a plossl works well in a Newtonian, or a Ramsden or Huygens in a refractor - these are invariably a good match for the scope they are used with. And a little optical analysis will show why.

Your asertion assumes all telescopes are more or less equally good - and give flat fields free of the monochromatic aberrations. That simply isn't the case - compare the field curvature of newtonians to that of refractors, as well as SCT and maks.

And you're right. Different telescopes produce different aberrations. Eyepieces, in general, have far fewer serious aberrations to put up with. I certainly would not state there are not differences. And those differences may justify spending more for eyepieces. And certainly there are interactions between scopes and eyepieces. But just about any modern eyepiece will do OK in the center of the field with just about any modern telescope.

It's already obvious that each type of eyepiece will suit some scopes, but not others, due to field curvature alone. Certainly not all. Several members in this forum have done side by side comparisons to establish this. To the extent a fair amount of buying and selling has occurred as observers try to optimise their eyepieces to match their scopes, once they know what works well - and what doesn't.

Again, you're talking about the outer edges of the field.

Anyone who made the mistake of buying Koenig eyepieces will understand this, most ended up fairly rapidly in the trash IMHO.

Konig designed 28 different eyepieces in his time at Zeiss, and the modern Brandon and Clave Plossls were probably his design--possibly the 5 element "Astroplanokular", too--so you are generalizing. And some Konig eyepieces work just fine in some scopes. Had the commercially-produced ones (I'm thinking University Optics here) been confined to 50 degrees, they would have given Plossls a run for the money in terms of longevity in the market.

There are other issues with specific eyepieces, too. Some Naglers are notorious for "kidneybean", due to excessive amounts of spherical aberration in the eyepiece.

Only the first generation of Naglers had this "spherical aberration of the exit pupil" and once it was identified was eliminated from all future Naglers. The eyepiece itself did not have spherical aberration. And if you used them in scopes where the eyepieces didn't produce overly-large exit pupils, they worked fine. I owned them all and though you had to hold your head very steady to avoid the kidney bean type blackouts, it was possible to do so. And the fields were sharp very far out toward the edge.

It's also evident that the designs of virtually all premium eyepieces since 2000 contain some amount of field curvature and negative coma, to suit fast newtonians while remaining tolerable in SCT's and maks.

Completely false. I know many of the designers, and there are no commercial eyepieces currently produced that have inherent coma correction. It would then make no sense for TeleVue, Explore Scientifics, Baader, GSO, Keller and others to produce coma correctors were that the case. An eyepiece that doesn't have astigmatism or lateral color induced by the fast light cone of a short reflector works fine at longer focal ratios. It's not an either/or proposition. Earlier eyepieces weren't designed with such short Critical Focal Ratio figures because the scopes didn't exist. In this era of commercially available scopes down to f/3 an eyepiece designer worth his salt would have to pay attention to that.

IMHO it's high time eyepiece manufacturers started to state which type of scope their eyepieces are optimised for, instead of keeping this a dirty secrecy and leaving observers the task of finding out by trial and error.

I've advocated for years that all manufacturers should state the Critical F/Ratio of their eyepieces, but I understand why they don't. If an eyepiece wouldn't work well in your f/4 dob, you wouldn't buy it. The literally thousands of posts from people who state that a certain eyepiece doesn't work well in their scopes but they love the eyepieces anyway says that a lot of observers aren't very fussy, either.
However, that Critical F/Ratio figure is available on-line for most designs.
Here is one such place:
http://www.brayebrookobservatory.org...fEYEPIECES.pdf

If this happened buyers might actually be able to make rational choices - instead of finding out by trial and error.

Well, the issue is the continued production of eyepieces only suitable for long focal ratio telescopes in this era of short f/ratio telescopes. If you care about star images in the outer field, and you prefer wide fields, you will pay for those eyepieces. If you don't care about wide fields, inexpensive eyepieces will serve you fine down to whatever f/ratio your telescope turns out to be.
Of course, one could just avoid Huygens, Ramsden, Kellner, Erfle, Monocentric, and Abbe-orthoscopic eyepieces and you'd be far likely to have better results. Judging from how many laudatory posts I read for some of those designs, though, quite obviously many users don't really care about the quality of star images in the outer field.

I have been tempted to set up an optical bench to test eyepieces and publish the results (I have a physics degree and a long background in ATM and have designed optics before). I'm also quite sure some manufacturers will have a heart attack at the thought of this, and would dearly love to kill that information off.

You might try looking at the published reports on the Ciel et Espace website. Here are a couple examples:
http://www.cieletespace.fr/files/Ins...aires_10mm.pdf
and
http://www.cieletespace.fr/files/Ins..._oculaires.pdf
If your browser doesn't automatically translate and you don't read French, you can cut and paste sections of text into a translation site like Google Translate.
They test eyepieces down to f/3.5 and publish wavefront error and resolution figures for their test subjects.