[rollei_list] Re: changing lens formulas
- From: aghalide@xxxxxxx
- To: rollei_list@xxxxxxxxxxxxx, <rollei_list@xxxxxxxxxxxxx>
- Date: Sun, 04 Nov 2007 23:49:41 +0000
After 4 years at /RIT and two weeks working for the fashion editor of the
Ladies' Home Journal I was recommended by C.B. Neblette for a position at
Modern Photography Magazine to replace the technical person who left to write
books and brochures about Polaroid products. That was 1957. Upon returning from
6-months active duty in Arkansas I worked with Optical Expert Ben Sherman to
create a lens testing method. Ben decided to use the U.S. Airforce targets and
test for resolution and call it lens sharpness.
This worked most times, but failed manytimes. Zeiss lenses for the Zeiss
Contarex tested badly for resolution and great for sharp images. Zeiss seemed
to be designed to give high contrast, as did many Nikkors which also failed in
resolution. Minolta did well with resolution and fair with contrast. Leica
lenses did well in both cases. So we didn't publish low contrast lenses because
we were really testing for high and low resolution not contrast. If the lens
failed a test we didn't publish the results.
Many years later they added contrast to the lens test. Ed Meyers
-------------- Original message from "Richard Knoppow"
<dickburk@xxxxxxxxxxxxx>: --------------
>
> ----- Original Message -----
> From: "Douglas Nygren"
> To:
> Sent: Sunday, November 04, 2007 8:51 AM
> Subject: [rollei_list] Re: changing lens formulas
>
>
> > Interesting thread, this. Let me add a point or two.
> >
> > A friend with an old Zeiss lens showed me a mark next to
> > an F stop. He said that probably came from the factory. He
> > explained that at one point the factory would pre-test
> > lenses and mark the sweet spot. I don't know if that's
> > true or not.
> >
> > My experience with a relatively new Zeiss lens on a Contax
> > MF 645 was that one particular lens was disappointing
> > except at one certain F-stop, where it is terrific.
> > People have a three-dimensionality to them.
> >
> > Until I found that spot, I used to curse myself for having
> > bought it. Now I'm glad I did.
> >
> > Doug
> >
> Unless one has access to factory archives its almost
> impossible to tell what the prescription for a given lens is
> beyond its generic type. There are perhaps a dozen or more
> patents from Zeiss Jena on Tessar type lenses including a
> few clearly experimental ones and some others from C.Z. in
> Oberchoken. Add to this perhaps a hundred patents on Tessar
> types from other manufacturers and you have some idea of how
> difficult it is to identify a particular commercial lens as
> being a particular prescription. Also, not all design
> variations were patentable.
> It is certainly true that there was relatively poor
> quality control of lenses up to WW-2. That was improved by
> the major manufacturers in both the U.S. and Germany after
> the war because war-time work required that a higher
> standard be applied. However, there is still a lot of
> variation between individual samples.
> To evaluate a lens requires that the aerial image be
> examined. This eliminates a lot of variables such as all the
> mechanical problems of a camera and the variables introduced
> by film. It is not too difficult to see at least major
> faults in a lens this way. Tests made in a camera actually
> test the entire camera and are subject to inaccuracies in
> focus and variations in the film plane.
> There is a tremendous amount of rumor about lenses and
> their design, mostly without any means of substantiating it.
> Some of it makes no sense in light of the fundamentals of
> optics and design.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
> ---
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