Re: [Rollei] Re: OT: retrofocus & inverse square

["Richard Knoppow" <dickburk >]

- ----- Original Message ----- 
From: "Jerry Lehrer" <jerryleh  >
To: <rollei  
Sent: Friday, January 09, 2004 2:29 PM
Subject: Re: [Rollei] Re: OT: retrofocus & inverse square


> Eric
>
> You actually want to put a FAN inside the lens? (rotating
star)
>
> Jerry
>
> Eric Goldstein wrote:
>
> > I'm waiting for someone to resurrect the clever Goerz
solution employed on this lens rather than have us buy a 400
dollar custom filter...
> >
> > Eric Goldstein
> >
> > -----Original Message-----
> > From: Richard Knoppow <dickburk  >
> > Sent: Jan 9, 2004 2:07 PM
> > To: rollei  us
> > Subject: Re: [Rollei] OT: retrofocus & inverse square
> >
> >    BTW, while the fall off of a "normal" lens is given
as
> > cos^4 theta (theta being the image half-angle) some
lenses
> > have more for various reasons. The famous Goerz Hypergon
is
> > an example.
> > ---
>
   It is a star-shaped rotating stop place outside the lens.
Its on a hinged arrangement operated by an air hose. The fan
is set in front of the lens at the beginning of the exposure
and falls away as it runs down. About half the exposure is
made through the stop and about half without it. Obviously,
the exposures must be long for this to be practical.
   The Hypergon is not corrected for spherical aberration so
must be used at very small stops. I think f/45 is the usual
operating stop. However, it covers something like 120
degrees. The well known Zeiss Topogon and Bausch & Lomb
Metrogon are related to this lens although both can be also
be classed as double Gauss types.

- ---
Richard Knoppow
Los Angeles, CA, USA
dickburk  

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