Lenses that function best wide open

"Rich" writes:

This is kind of interesting. Right now, you can buy a hyperbolic
astrograph (a mirror lens) with a 500mm focal length and an f2.8
aperture. It costs about $4,500 and will support up to a 35mm image
size.

Does it have a flat focal plane? Sky surveys are usually done with
Schmidt cameras with very fast f-numbers, but the focal plane is curved
and cannot be made flat. Gelatin emulsion on film can be stretched
slightly into the curved surface required, but you can't do that with a
CCD.

Dave

"Rich" writes:
Has anyone ever run across any lens (outside of very long ones,
exceeding f10 focal ratios) that performs best wide open? In other
words, the residual aberrations don't decrease noticeably upon stopping
the lens down.
If so, what lens, and what camera was it used with?

I once saw the results of optical tests performed on the Nikon 120 mm
f/5.6 macro lens. This is a view camera lens intended for 1:1 work (it
looks internally symmetric). Its resolution was best wide open (I don't
remember if that was on-axis resolution or over the whole field) though
it vignetted a fair bit wide open.

Dave

[A complimentary Cc of this posting was sent to
Rich
], who wrote in article . com:
Has anyone ever run across any lens (outside of very long ones,
exceeding f10 focal ratios) that performs best wide open? In other
words, the residual aberrations don't decrease noticeably upon stopping
the lens down.

IMO, as stated, this does not make a lot of sense. You should specify
in which part of image circle you are interested, and whether sagittal
or tangential aberration is important.

It is not impossible to believe in f/2.8 lens which performs best wide
open IN CENTER. On the edge - almost improbable; especically for
sagittal aberration...

Hoep this helps,
Ilya