On Fri, Jan 27, 2012 at 9:56 AM, <erikhansen@thebluezone.net> wrote:
Chuck, have you made a Nagler?
No, no modern "exotic" designs. I don't grind my own eyepiece lenses (yet) so I'm limited to what's available in the surplus market. You don't see surplus Asian-manufacture eyepiece lenses showing up at Surplus Shed. I'm sure Al Nagler contractually demands that "seconds" be destroyed, anyway. Modern, ultra-wide-field designs have departed from traditional eyepiece formulae thanks to new glass formulations and computer-aided design. The amateur certainly could produce such an eyepiece, but it probably wouldn't be cost-effective given the investment in time and procurement of the glass needed. Those designs that use aspherical lenses are even more problematic. Traditional refractive optics use spherical surfaces almost exclusively. Much easier to polish and figure. Spherical lens surfaces are are manufactured by machine, from beginning to end. Aspherical surfaces need the human touch to figure. You have to remember that Plossls, symmetricals, Konigs, Kellners, and Erfles are all really variations on a theme. There is no hard-and-fast rule that defines them (except the symmetrical design, of course). I've managed to sneak-up on about a 65-degree AFOV with my home-brew stuff, before edge aberrations become objectionable or the field gets objectionably curved. Beyond that, you're into Nagler territory and out of the land of the bottom-feeders. ;-) If you're wondering why modern eyepieces such as Naglers cost about as much as a good-quality camera lens, it's because, essentially, they have as much or more glass in them, with similar curves, as good-quality camera lenses. In fact, when you take into account that there are a lot fewer eyepieces sold than camera lenses, the costs become a lot more reasonable. Trivia: The basic Nagler wide-field design came from Al Nagler's working with the Apollo space program imaging team.