Re: [APML] (OT) IC1396 CCD with Schmidt-like FOV

[Chris1011@aol.com]

In a message dated 8/6/2002 10:15:57 AM Central Daylight Time, robgendler@worldnet.att.net writes:


> The one advantage of the camera lens is that they are fast.
> Correct me if I'm wrong but a 300mm F4 lens fully apochromatic
> for astronomical imaging would be a challenge to make.


A straight lens, yes. But manufacturers can cheat by using a long lens, say F8, and then adding a rear .5x telecompressor unit. Both Tak and Televue are already doing this in their new 4" refractors. It's an old concept called a Petzval. In fact, 35mm theater movie projectors use Petzval lenses and they come as fast as F2.5. When I worked at Bausch and Lomb in the late '60s, we made them with apertures up to 100mm diameter, F3 to F4. Used wide open, they had terrific resolutions with no astigmatic seagull images at the field edges, unlike modern double Gauss designs. They were not apochromatic, of course, but this can easily be done now with modern ED glasses.

Roland Christen