Re: My 7p Realist!!!

[P3D Eric Goldstein <egoldste@xxxxxx>]

Dr. George A. Themelis wrote:

> I contacted John
> and asked him about converting a 2.8 to 7p.  The 4-element lenses of the
> 2.8 could (at least in theory) do the job as well as those in the
> Belplasca.


Except a Tessar ain't a Tessar ain't a Tessar!

One tessar design is not necessarily the equal of others. Different
element design and placement as well as different glass types and
coatings all factor in. In terms of the lenses found in stereo cameras,
the David White tessar type lenses perform differently from the
"Germany" lenses, which are different from the Ektars, and the Zeiss
belplasca lenses seems to best them all having been recalculated from
prewar designs to take advantage of so-called rare earth glass and
proprietary coatings (though I have one source which also claims this
may also be true for the Ektar lenses).

In terms of coverage, the belplasca's zeiss tessars have 37.5 mm lenses
instead of the usual 35 mm (or 36 mm for Ektars). This 7ish% increase in
focal length may very well have been deployed to gain better coverage of
the 7 perf format.


Eric G.


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