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Thread: How different are Tessars from different companies?

  1. #21
    Drew Wiley
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    Re: How different are Tessars from different companies?

    The whole point of a smaller aperture is that it mechanically vignettes off the lower resolution parts of the image circle. Guess that's why they termed em Commercial Ektars. Portrait studios typically wanted faster aperture, shallower depth of field, and weren't as concerned about corner resolution, so coveted 4.5 versions. Someone else can describe the specific Ektar options better than me; but Zeiss and others had more than one speed/size selection of tessar. I have a Zeiss f/9 360 barrel process tessar that is extremely sharp over its whole image circle, but still renders lovely out of focus background blur. By contrast, my Nikkor M's are thin elements for a tessar design, especially contrasty, being multicoated, but also clinically sharp with the busy annoying background blur typical of Nikon LF lenses, so wonderful for intentionally sharp landscape subjects, but not ideal for anything "dreamy". The 300 M is extremely sharp on 8x10, but with very little to spare, so not really very versatile on this big a piece of film. I mostly enlarge my negs, so a contact printer might have a more liberal definition of usable image circle than I do, as well as at how small a stop detail rendition becomes unacceptable. Probably very few ULF shooters enlarge their negs. And certain applications, like studio portraiture, don't require significant tilts or rises. So it's all relative.

  2. #22

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    Re: How different are Tessars from different companies?

    Quote Originally Posted by John Kasaian View Post
    Interesting. Does it have anything to do with having the more open aperture of 6.3s? But then how would that explain the f9 450 Nikkor M which covers 12x20 with coverage to spare?
    Not at all. The prescriptions are different.

  3. #23
    Drew Wiley
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    Re: How different are Tessars from different companies?

    I suspect even the glass types are significantly different because traditional LF tessar elements are quite thick and heavy relative to diameter, whereas Nikkor M's are rather thin, compact, and lightweight.

  4. #24

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    Re: How different are Tessars from different companies?

    Quote Originally Posted by Drew Wiley View Post
    I suspect even the glass types are significantly different because traditional LF tessar elements are quite thick and heavy relative to diameter, whereas Nikkor M's are rather thin, compact, and lightweight.

    Nikkor M series has no extraordinary glasses, lenses in the nikon range sporting some expensive glass elements are T and AM series.

    A 4 elements and 3 groups design cannot correct all well, and some sacrifices are required in one feature or other, I suspect that M design allows some field curvature (like many Tessar designs) to be good in other fetures. This would be painful for architecture, but anyway it lacks and ample circle (around 55) for that application, so no problem.


    I find the M a bit harsh in the Out Of Focus backgrounds, of course it can be used for portraits but one has to be aware about that, because subject isolation is not the same than with a Xenar, for example.

  5. #25
    Drew Wiley
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    Re: How different are Tessars from different companies?

    C'mon, Pere - do you have a spy inside Nikon optical engineering discovering the secrets of their specific glass types per application; or have you gone out, bought a lens, and sent it through a mass spectrometer to identify the elemental composition, or are you merely guessing? Fortunately, I don't need to guess the answer to my own question. Do you even actually shoot these lenses? I certainly haven't detected any field curvature; but at f/9, most of the sloppy part of the image circle has been cropped out for a realistic film format sizing. They aren't specific for apo graphics applications anyway, like process lenses. And they don't have images circles as generous as plasmats or wide field four-element dialytes, and their out of focus rendering is indeed noisy; but in certain other respects, like sharpness and hue rendering, they are exceptional.

  6. #26

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    Re: How different are Tessars from different companies?

    Quote Originally Posted by Drew Wiley View Post
    C'mon, Pere - do you have a spy inside Nikon optical engineering discovering the secrets of their specific glass types per application; or have you gone out, bought a lens, and sent it through a mass spectrometer to identify the elemental composition, or are you merely guessing?
    Drew, quite easier... check the nikon catalog, they show off what lenses have special ED glass which is much more expensive and imposes a larger lens. Those elements painted in yellow are the expensive ones. http://www.kennethleegallery.com/pdf...rmatLenses.pdf


    "A Tessar comprises four elements in three groups, one positive crown glass element at the front, one negative flint glass element at the center and a negative plano-concave flint glass element cemented with a positive convex crown glass element at the rear."


    Tessar is crown and flint, no ED.

    M is a great field lightweight lens, but nothing extraordinary, I feel it was expensive for what they gave, so a good product for Nikon.

  7. #27
    Drew Wiley
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    Re: How different are Tessars from different companies?

    Where are you getting that information, Pere? Sure, I've got a copy of Kingslake who describes how tessars were first invented that way long ago. Many many specific glass types have evolved since the crown vs flint option. There are also ways lens element performance can be significantly altered via specific coatings. In this case, a little knowledge is dangerous - another old saying. You know just enough to think you know something you really don't know, and it shows. I have that Nikon LF brochure you linked, and it doesn't indicate the specific glass at all in this case. And as far as high-dispersion glasses go (which aren't necessarily all the same either), they are appropriately chosen when needed, but are not in themselves an indicator of superior quality if a lens can achieve its intended performance using other glass types, which might not be cheap either. You're oversimplifying the entire subject. A real optical engineer might or might not have the answer. Both Nikon and Fuji can be somewhat secretive at times about lens details.

  8. #28
    Mark Sawyer's Avatar
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    Re: How different are Tessars from different companies?

    There were several types of new glass, including new variations of crown glass created by Otto Schott for Zeiss around 1887 through to 1893 that made anastigmats possible. (The old crown and flint combinations couldn't correct for astigmatism.)

    Edited from the Zeiss site regarding the Tessar:

    (Referring to the Zeiss Anastigmat/Protar that preceded the Tessar): This was different with the new achromats made from the new types of glass melted by Otto Schott. These new types of glass were known as dense crown glass because they combined a relatively high refractive index with lower color dispersion. The combinations of refractive index and dispersion now available enabled a cemented surface in achromats with a collective effect, which could be used to correct astigmatism. However, with the new achromats, very little could be done to influence the spherical aberrations. Therefore, it was a logical idea to combine both types of achromats with complementing properties to create a lens in which an old achromat was used for the front element and a new achromat for the rear element.

    BTW, Zeiss notes about the Tessar:

    Simply the advances in glass technology, similar to the time of its birth, enabled performance increases which also demonstrate the potential of the basic idea. From the outside, a Tessar from 1920 looks exactly the same as one from 1965, but the image quality of the newer lens is considerably better.


    Lots of history here:

    https://lenspire.zeiss.com/photo/app...ar-2011-EN.pdf
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  9. #29
    Drew Wiley
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    Re: How different are Tessars from different companies?

    And those glass improvements were a century ago, Mark. I got a catalog supplement of optical glass types the other day from just one distributor, and there were about twenty new options added just past year, added to the hundreds already available. I tossed the list because I didn't need it. Now the big push in innovation is for improved laser and machine vision optics. Kingslake ended his account of lenses once things got to the 1960's, simply because traditional tinkering was beginning to be replaced with space age science, followed by computerized design. Many of the old stereotypes no longer applied. But thanks for the fun Zeiss link. Interesting that the tessar design has been used for cell phone lenses; but it doesn't affect me because I don't take pictures with a phone.

  10. #30
    Mark Sawyer's Avatar
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    Re: How different are Tessars from different companies?

    Quote Originally Posted by Drew Wiley View Post
    But thanks for the fun Zeiss link...
    Yup, wasted half an hour of my time...
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

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