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Re: [Rollei] OT: retrofocus & inverse square


It's not really an inverse square function.  I have the write-up
that shows it to be a cosecant square function.  I believe it was used in

the analysis of a radar antenna coverage.  They drew the analogy of a
wide angle lens and its image.

BTW, my 20mm Nikkor shows about the same "dropoff" as my 21mm
Super Angulon did.  (But I still wish I had it back!)


john wrote:

> Heres a "curiosity-kills-cats" question for Richard...Do retrofocus
> wideangle lenses suffer the same corner brightness dropoff as a
> symmetrical design, or does their increased distance from the film
> reduce the effect? If not, it would appear there is a free lunch
> after all. My Nikkor 20mm seems to be reasonably even...no need for a
> graduated filter. I don't have a Leica Super-Angulon type lens to
> compare it with. -- John