The 1900 Heliar design was essentially a modification of the Cooke
Triplet. (previously took 8 to 10 elelments to achive that reduction in
aberrations) It is still a popular configuration.
http://www.willbell.com/tm/ChapterB.3.pdf
Two addtional elements were added in a symmetrical layout.
Interestingly the Tessar design adds one element only to
Cooke triplet. ---See Figure B.3.3.1 in the pdf. (page 35) Tessar
means four, No? So your observation is spot on. I believe these
types of lenses are aberration, not diffraction limited for the most
part.
The CV 50/3.5 Heliar essentially looks like it could be in the 1902
patent, but is very nice indeed. Must say I had briefly "seen" the
lens design of the CV 75, but it didn't register. It seems to have
rendering qualities similiar to the original Heliar but I don't
understand the naming of it at all. Perhaps it is marketing decision.
APO dosen't seem to mean as much anymore either. I appreciate this
eagle- eyed list catching that.
Heliarless Mike
CJS writes:
>AFAIK, the Heliar (like the current, highly acclaimed CV 50/3.5) is a
>three-group, five-element design -- much like a Tessar with a cemented
>doublet instead of the front element <
>http://www.cameraquest.com/jpg6/VC10153.jpg>
>But the 75/2.5 looks like yet another formulation of the Planar /
double
>Gauss: <http://www.cameraquest.com/jpg4/vm-75.25.gif>
--
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