What lens design is this?

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Planapo
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Location: Germany, in the United States of Europe

What lens design is this?

Post by Planapo »

Could anybody tell me if the lens shown in the following link is of the "6 elements in 4 groups design"? (Could also be called a "6 elements in 2 groups design" from my naive perspective).

http://www.schneider-kreuznach.com/indu ... 80_1VD.PDF

And would this lens be still called a symmetric lens? :?

Thanks in advance!
--Betty

rjlittlefield
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Post by rjlittlefield »

Yes, 6 elements in 4 groups. The key is to notice that the outer two elements on both sides appear to have the same curvature on their inner faces. They are probably cemented pairs. The term "group" usually means one element, or multiple elements cemented together so there are only two air surfaces. If the elements did not quite have a common curvature and thus were not cemented, then it would be 6 elements in 6 groups. That's not as silly as it sounds -- many of Canon's telephoto lenses are described as "8 elements in 7 groups", or something similar.

About the rest of the nomenclature, see http://www.winlens.de/en/lensde_opticalimg.html .

The lens design that you link to appears to have an entrance pupil diameter of 14.6 mm, but an exit pupil diameter of 17.3 mm.

This is an enlarging lens, so I'm guessing that by "entrance pupil" they mean the side nearest the film, where the light would be coming in. If so, then when you reverse the lens for stacking, that same pupil applies, and the lens will continue to act like what you would expect for f/4. If not, it may be even better because the other pupil is larger. The difference in pupil sizes is not much anyway, only 1.18X.

Bottom line, the lens is not symmetric, but I don't think this will have much effect on how it works for you.

--Rik

Charles Krebs
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Post by Charles Krebs »

Hi Betty,

Yes this woiuld be a "6 element, 4 group (or "lens") design". The two outer elements are cemented together, so they each comprise one group. The inner two elements are "air spaced" so they each comprise another group.

Great lens. Originally designed for enlarging "645" format.


(oops... Rik beat me to it ...)

rjlittlefield
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Post by rjlittlefield »

Hee hee hee...nosed 'im out by 2 minutes!

--Rik

Planapo
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Location: Germany, in the United States of Europe

Post by Planapo »

Thanks Charlie and Rik for enlightening me!

So it´s the air spaces, even little ones that divide the groups which are cemented, and the equal size of exit/entrance pupils that make the symmetry.
That winlens.de is a very informative link. Bookmarked!

Charlie wrote:
(oops... Rik beat me to it ...)

Rik wrote:
Hee hee hee...nosed 'im out by 2 minutes!

Betty comments:
Aah yeah, ... quick Rik once again! :D

--Betty

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