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Re: Re: [Rollei] Planar Sharpness

At 06:00 PM 04/01/2002 EST, you wrote:
>I have an F w/f3.5 Planar, 5 element version   t is usually quite 
>sharp centrally at all apertures, but has to be stopped down to f11 to 
>achieve edge to edge sharpness.  The lens looks good as far as I can detect 
>and has been examined by both Harry Fleenor and Marflex and pronounced fit.  
>I figured maybe curvature of field or film flatness issues.  Could it 
>possibly be separation?  How does that manifest itself on film?
>Allen Zak
  Separation should be visible on examination of the lens. Shine a
flashlight through it and look for bubbles in the cemented elements. 
  The Planar/Xenotar is supposed to give better corner performance than a
Tessar at the same stop. This lens should be doing better. Whatever the
aberration is its more likely to be caused by a mis-spaced element or
something of the sort. 
  You can tell somethign about what is going on by putting a piece of
ground glass over the film gate and examining the image visually using a
magnifier. That will show whether the bluring off axis is due to field
curvature or something else. Both coma and spherical aberration are reduced
by stopping down. 
 If the effect is not apparent on the ground glass it may be due to film
flatness. An auto colimmator or laser interferometer could tell about this.
Unfortunately, I've left my interferometer in my other suit. 
- ----
Richard Knoppow
Los Angeles, CA, USA