[rollei_list] Re: changing lens formulas

There was actually relatively poor quality control from many lens
makers well into the 60s and 70s; factory tolerances told the story.
Until automation yielded tighter manufacturing tolerances for overseas
makers, which really began in the 70s but did not become wide-spread
till the 80s, there was very significant individual variation from
even the best manufacturers...


Eric Goldstein

--

On 11/4/07, Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:
>
> ----- Original Message -----
> From: "Douglas Nygren" <dnygr@xxxxxxxxxx>
> To: <rollei_list@xxxxxxxxxxxxx>
> 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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