Re: [Rollei] 6-element planar?

[Carlos Manuel Freaza <cmfreaza]

 The architect Vogeler, a German descendant, amateur
photographer and Rolleiflex fan, referred me that in
the early 1960s he read an article about the new 3.5 F
from a German magazine on photography. He remembered
this article commented that F& H wasn?t satisfied with
color performance of 3.5 Planar and Xenotar 5 elements
lenses with respect to new color films. There was some
little problem with the color fidelity transference
from the five elements 3.5 lenses to the new color
emulsions.
 The color photography had a spectacular increase,
Agfa, Kodak, Perutz, Ferrania, Ansco Gevaert ,etc.
often launched new color films and F&H  wished
maintain their high quality standard.. The architect
believed that the problem was the ?60s new emulsions,
not the lens, because he had a Rolleiflex 3,5E with
Planar 5 elements and a 3.5 F with Planar 6 elements
and there weren?t color performance differences using
?90s color films.
I don?t know if the article have a technical reason,
but it?s an interesting testimony from that time.
All the best
Carlos     

- --- Richard Knoppow <dickburk  > escribió:

>   I am frustrated by my lack of German. It appears
> that
> Prochnow addresses all this in some detail on pages
> 16-375 -
> 16-376 of _Rollei Report 2, but I can make out only
> a little
> of it.
>   The reasons for changing the design would be
> interesting
> to know. If the "official" explanation is that it
> was to
> increase edge illumination it doesn't make a lot of
> sense.
> Edge _sharpness_ would, presuming the extra element
> allowed
> better correction of rim rays.
>   The six element lenses are true Planar or Biotar
> types
> with the advantages of semi-symmetry. A symmetrical
> lens is
> automatically corrected for coma, geometrical
> distortion,
> and lateral color. Since coma is proportional to the
> image
> angle a symmetrical lens might well be sharper off
> axis than
> a similar asyemmtrical lens. A symmetrical lens
> cancels
> these aberrations when the entire system is
> symmetrical,
> that is, when object and image distances are the
> same,
> although the cancellation even at infinity is
> considerable.
> By shifting some power the maximum cancellation can
> be
> adjusted for some other conjugate, a technique used
> in a
> great many lenses. This is the main difference
> between the
> original Planar and later developments from it like
> the
> Biotar or Opic.
>   Its interesting that both the Zeiss and Schneider
> f/3.5
> lenses have cemented surfaces which are planar. This
> would
> make them easier to manufacture. The f/2.8 Xenotar
> also has
> a plane cemented surface but the five element Planar
> has a
> rather steeply curved cemented surface with a rather
> thin
> first element. It must have been expensive to make
> and that
> might be another reason for dropping the design. I
> suspect
> the prescriptions for all of these lenses are
> available. It
> would be interesting to set them up in Zeemax, or
> some other
> lens design program, and see what the performance
> curves
> look like. A program like Zeemax can also calculate
> the
> sensitivity of the designs so you could find out if
> one or
> another might have been very difficult to make.
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk  
>  

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