[Rollei] Re: Why the 6-element lens for 3.5Fs

[Eric Goldstein <egoldste >]

Richard Knoppow wrote:

> Since some report good performance from these CZJ Tessars
> the design was not the problem. In general Tessars are not
> at their best at f/2.8 but can be quite satisfactory.


In his book "Photographic Optics," (1950) Allen R. Greenleaf states that
Tessar designs are optimal as f/6.3 lenses, and no matter how carefully
designed and constructed, versions faster than f/3.5-4.5ish "would not
satisfy a critical user." (Mr. G himself seems like quite the critical
fellow!)

Today, even with modern glass, design and fabrication, Tessars of f/2.8
speed are produced for miniature use only...


Eric Goldstein

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