Triplets, Tessars, Sonnars, Optical Innovation, and the Nikkor-P

Discussion in 'Classic Manual Cameras' started by jdm_von_weinberg, Mar 23, 2013.

  1. Triplets, Tessars, Sonnars, and Optical Innovation

    This is going to be very basic for some of you. It's also derivative. I wasn't sure whether to post it or not and where, but it's kind of long to tack on to another forum; and, since I had to plow (plough) through it to try to get it clearer in my own mind, I sort of hope that it may be useful to somebody else as well to have it drawn together from the various sources.

    I have long since struggled through Photographic Optics, 13th ed. 1966 by Arthur Cox, M.A., B.Sc.F.Inst.P. London & New York: Focal Press. Some sections more than once, and I have carefully annotated some of the discussion and figures (in light pencil, I'm not a vandal, just a Goth from Gotland).

    I will recommend the book to you with some reservations. The history of photography and optics is no more clear of local prejudice than is any other branch of history. Cox, as his titles show, is definitely a Briton. So naturally enough, Cox tends to see the history of optics in fairly British terms. This is not so much wrong as it is a little provincial, but the Germans, Americans, French and citizens from other places with 19th and early 20th c. optics industries are just as provincial in their own ways.

    One of example of this, just in passing, is that Kodak (an important innovator, to be sure) features rather more prominently on Wikipedia's discussions of optics than it does in Cox or more easterly sources.

    Anyhow, some recent discussion on this forum led me back to Cox and some other sources to see what was what, since (unfortunately) reading something is not at all the same as "grasping" it.

    I am fairly dependent on Cox here, having looked on line for newer optical histories, only to find out that the European ones, at least, are a LOT more expensive than the old cameras I putter around with, and even as much as a lot of the lenses I am also accumulating and using. So Cox is what I have to work with, plus what look to be pretty good sources on Wikipedia (I am always amazed at how well Wikipedia does with non-political/non-controversial subjects).

    Why am I telling you this?

    Well, on a recent comparison of a Carl Zeiss Jena (Olympia) Sonnar 180mm f/2.8 lens with a Nikkor-P 180mm f/2.8 lens ( ) I said:

    "These are clearly in the same family"

    To which Q. G. de Bakker and Rick Drawbridge expressed skepticism about this "family". Q.G. also suggested that the Nikkor was more like a "Tele-Tessar."

    I'm here to say, that I was right (as I tend to think ;) ), but in the manner said in Star Wars, "So in a way, I was right when I said he had killed your father …"
    I was sort of right about a 'family resemblance', but what I was seeing, given a generous dispensation, was not a Sonnar family resemblance but rather a similarity of what our good source, Mr. Cox, calls "Triplet Derivatives".

    So, what I am proposing to do here is to follow up to see what this all means.

    Cooke Triplet
    Cox says
    "When H. D. Taylor developed the Cooke triplet lens (named after the optical manufacturing company Cooke and Sons in York, England) a step was taken which was of
    the greatest importance, as far as the design and production of photographic lenses was concerned. An early form of the lens is shown in Fig. 88a. It represented a complete break from existing tradition, as constituted at that date by Petzval lenses and by early symmetrical anastigmats." p248


  2. Tessar

    The next step in development of this triplet form?

    "The most important single development, along these lines, is the replacement of the single rear element by a cemented doublet in the Tessar form of lens, shown in Fig. 89a. The refractive index of the negative element in this rear doublet must be less than the refractive index of the positive element in the doublet." p252


    Here is what Cox is talking about

  3. Sonnar

    After some discussion of lenses like the Ektar and Pentac, Cox comes to the Sonnar.
    [Wikipedia: ( )]

    "The culmination of this line of development is found in the Zeiss Sonnar and Biogon constructions. The Sonnar lens, two versions of which are shown ln Figs. 90d, e, may be regarded as being derived from the lens of Fig. 90a by absorbing the central negative lens into the second member, or partially into the second member and into the third member. With this design an important feature is the thick second member. This serves the same general purpose as the thick negative members in the Speed Panchro, namely to reduce the Petzval sum. "

    Here is the figure that Cox refers to [slightly modified to label the parts directly]
  4. Summary

    No conclusion is warranted, but I hope that this makes the salient characteristics more clear.

    The "critical attribute", as we say in archaeological taxonomy, for a Tessar is "the replacement of the single rear element by a cemented doublet "
    For a Sonnar, "the thick second member".

    Since Zeiss named it a Sonnar, the Olympia Sonnar is clearly a Sonnar.
    The Nikkor-P, is a Nikkor-P; but, yeah, it does look like a lot of the large number of variations of the Tessar design.

    On the other hand, ta-da, both Tessars and Sonnars (and many others) can all be seen as "Triplet Derivatives" as Cox calls them. :)

    Now will somebody here who actually knows something about lenses, please explain to me in simple words how to determine the lens formula or at least component number from the darned reflections?
  5. Actually the Sonnar (with its signature cemented triplets) was a development of the Ernostar (itself derived from the triplet.) The 180mm Nikkor P went the opposite way, going back to an Ernostar design, as did Zeiss with their SLR Sonnars, all of which dispensed with the cemented triplets, no longer necessary with the advent of multi-coating and high reflective index glass.
  6. More at
  7. A long time ago, in a galaxy far, far away...That's a pretty lucid presentation of some optical mysteries, JDM. I hadn't intended to imply that I thought your comparison was in any way wrong, merely not quite as close as you opined, but this post of yours very capably demonstrates the fluid nature of optical terminology and classification. I wish I knew and understood more, but on some other forums it can sometimes get fiendishly close to hair-splitting and navel-gazing. Thanks for a scholarly post.
  8. What this demonstrates is that when you go back long enough in time, to when the present day variety had yet to begin evolving, you'll find that 'all things' were pretty much 'one thing', from which that present day variety has evolved. If you ignore the separate ways things have taken to become the different things they are today, everything is 'family' of everything.<br>Sonnar, Tessar, Biogon, Ernostar, and many, many more that have not been mentioned: they are all just Cooke triplets that have been messed with.
  9. Thanks for posting such detailed info JDM. I've been curious about these triplets, as I'm thinking of selling my "better" lenses and using triplets exclusively. They do everything I want, and more. If I was shooting landscapes I would go with something that's sharper in the corners, maybe, but the triplets I have are really sharp in the center (where my subject usually is), have nice bokeh, and have a look that I like. My next experiment will be to replace my beloved Leica R 90 2.8 lens (seems to be a lot of elements in there) w/ a M42 mount 135 f4. Shots I've seen from those look very good, and I could buy three of them for the price of the Leica lens. 135mm is a little long for portraits, but I can't find an 85 or 90 Triotar.
  10. Fred, the symmetrical lenses are, according to Cox, and I think quite logically, as close to another 'family' as you can get. The modern Biotars and kin are among my very favorite lenses.
    QG, you noted, of course, that I was actually saying pretty much that you were right, "in a way". ;)
    In a day where photon squeezing is not so necessary as it once was, the Tessars and kin are definitely "back", not that they ever went away.
    Thanks for your comments, all.
  11. All of the above and more. Many used to say the Tessar was a derivative of the Cooke triplet. Now we see where this line of thinking comes from. Many others have opposed this line of thought ..saying the Tessar was the breakthrough/out lens and a clear departure from the Triplet. So it's nice to see the marrying up of the derivatives to the Triplet. The Triplet being as you said a break from the Petzval and the symmetry of the previous designs. Everything that's new and different is really old ...again!!
  12. A similar discussion was undertaken by Roger Cicala on the blog titled "Lens Genealogy, part 1 and part 2" Interesting article, well worth a look.
  13. Nice presentation. If you haven't read "A History of the Photographic Lens" by Rudolf Kingslake of Kodak, it's well worthwhile.
  14. Um, JDM, the story that Rudolph developed the Tessar by modifying a Cooke Triplet circulates widely but some sources, including Zeiss, deny it strongly. See Kingslake ( , p. 86) on this.
    Its better, on the whole, to believe the man who did the work than people who made up stories long after the work was done.
  15. Very interesting JDM. Actually the Cooke Optical Company still exists in Leicester, UK, making lenses for the film industry, and was recently awarded an Oscar. I don't know if they make triplets anymore but their lenses are valued for the "Cooke look" apparently.
    It's descent was traced via the famous Taylor Taylor and Hobson lens company, later Rank Taylor Hobson, also in Leicester, but I don't know the full story.
  16. Its better, on the whole, to believe the man who did the work than people who made up stories long after the work was done.​
    but as I said somewhere else, a successful design has many inventors.
    Nor, as I already said, are the German sources necessarily less 'provincial,' given all the nationalisms that are intertwined with this topic. I confess a leaning toward Jena, myself, but look at the lens diagrams for the "Cooke Triplet" and the Tessar, eh?
    "Small step for man, giant leap for mankind."
  17. JDM, Paul Rudolph invented the Protar, the Unar, and the Tessar. In that order. These successful designs have one inventor. The Tessar has a Unar front group and a modified Protar rear group. What they look like has no bearing on how Rudolph came up with the design.
    H. D. Taylor of Cooke, later Cooke, Troughton, Sims, invented the Cooke triplet. One inventor.
    All of the design types mentioned were original, i.e., not derived from earlier designs. It is not always the case that a successful design has one inventor.
    John, today's Cooke Optics derives from the lens-making part of Taylor, Taylor and Hobson. I believe that TTH's former metrology division still trades as TTH. TTH licensed H. D. Tayor's design from Cooke, sold triplets as Cooke triplets. As time passed Cooke became a TTH trade name and lenses of many design types were badged Cook. Cooke Optics current line of cine lense have nothing in common with the Cooke triplet but the word Cooke.
  18. JDM, Ludwig Bertele designed the Ernostar and later, the Sonnar, neither of which belongs to the "symmetrical family." (I see you only looked at the URL I mentioned, not the web page.)
  19. Look, as said, I like the Jena story better myself, but it simply isn't black and white, either.
    It's good to see that Zeiss chauvinism is not dead, however.
    I feel good about that, especially given that the preface to my discussion above was precisely a disclaimer that Cox was a little, well, British.
    However, are you seriously proposing that people in one place had no idea what was going on in other places at the same time?
    I never said anything about the Sonnar being "symmetrical" - indeed the whole point of this post was to trace the non-Planar/Biotar/etc. designs.
  20. And I never mentioned anything symmetrical in this thread. I wonder where this came from?
    Fred, the symmetrical lenses are, according to Cox, and I think quite logically, as close to another 'family' as you can get. The modern Biotars and kin are among my very favorite lenses.​
  21. Fred - I was responding to your link to the Double-Gauss discussion included at the site on the "history of fast lenses"
  22. John, thanks for the informative articles at I have bookmarked them for future reference.
  23. Steve, the ZM Tele-Tessar 4/85 (3 optical groups) is the modern version of the Contax mount 4/85 Triotar.
  24. JDM, if you bothered to look at the webpage on that link, you would have seen an extensive discussion of Ernostars and Sonnars right at its beginning.
  25. "QG, you noted, of course, that I was actually saying pretty much that you were right, "in a way". ;)"

    I think i forgot to indicate that by adding a ;-)

    It's a tricky thing, talking about lens families based upon what they started out as, since the important bit is why they were made different, and how.

    I agree with Dan that lenses that embody the same idea do not necessarily have a common ancestor as such. They do have a common idea in their ancestry though. Triplets are based on a peculiarity in the Petzval theorem first noticed and employed by Taylor.
    And i would disagree with the assertion that the Tessar is not an elaboration of that idea. It's not an Unar with a modified Protar rear group. It's a Cooke with an achromat as rear group. Just like the Heliostigmat is a Cooke with an achromat as front group, the Heliar is a Cooke with an achromatic doublet both in the front and the rear, and the Hektor is a Cooke with achromatic doublets in all three positions.
  26. JDM<br>You keep dragging in your favourite, the Biotar.<br>Did you know that the original Biotar (i.e. not the lens Zeiss East branded Biotar, to avoid the Planar name) is not a derivative of the Double-Gauss Planar, but yet another elaboration of the triplet?<br>The performance of triplets starts to fall apart at wider apertures. A solution employed to keep spherical aberrations and coma in check was to add another element. Most of these faults originate in the rear element, and one solution is to split the thing in two, keeping the same total power, but reducing the curvature, and thus spherical aberration and coma. Examples are the Tachar, the f/2.5 Cooke, and the f/1.9 Cinor B.<br>But it doesn't have to be the rear that provides the solution; another direction was taken in the Hektor: split each element, and you get more curved surfaces you can use to control the performance of the lens. The fast Hektor-Rapid, which evolved out of the Hektor, went one step further and (as did the Tachar) added another separate lens element, in the front (where the Tachar had one added in the rear).<br>There are two more places where you can add an extra correction lens in the triplet, between first and second, and between second ans third element/group. The Xenar put the extra lens between the front positive lens and middel negative lens of the Tessar-type triplet. (The (original) Sonnar filled the air space in the Xenar between that extra lens and the middle negative lens with glass.)<br><br>And the (original) Biotar is an example of a Tessar-type triplet with the extra lens added between the triplet's middle negative lens and the rear achromatic doublet.<br>It is not a member of the Double-Gauss family.
  27. And i would disagree with the assertion that the Tessar is not an elaboration of that idea. It's not an Unar with a modified Protar rear group.​
    QG, naturally I can't find the quotation when I need it but I believe that's what Rudolph said he did. I prefer to believe the inventor's explanation than after-the-fact one you and JDM prefer. That the two explanations describe the same lens is fine, but since they differ they can't both explain the process by which it was invented.
  28. Dan,<br>I too would tend to believe what an inventor himself said.<br>I would also be wary of an inventor not being aware of a very succesfull new thing that appeared in his particular field of work, claiming not to be influenced by it in what he then invented, which turned out to look uncanningly as if he did know of and was influenced by that thing after all.<br>The Cooke Triplet triggered a slew of new triplet and triple derivative designs, and it would be rather remarkable if the Tessar would not be one of them.<br>People are people and can't help but do what people do. Rudolph is not immune to that.
  29. QG, I'm sorry you don't buy Rudolph's story. Kingslake did, see the link I posted in what, IIRC, was my first post in this discussion.
  30. People had time back then, James. Mainly because they did not waste it on all those time wasters that turned our days into more 'modern' times... They still knew how to spend their time well.<br>A nice example from the lens design world of how the believe in technological progress falls flat is the Zeiss 38 mm Biogon. It was designed in the days that people used slide rules, pencils and lots of paper. It had to be redesigned some 40 years later, and brute computer force did not produce a better lens (in fact, it was a tiny bit less good) than the slide-rule original.<br>In short: just because something was done long ago doesn't mean people didn't know what they were doing back then and the thing did not get done properly.
  31. Dan,<br>As far as i am concerned, the jury is still out, and will never return a verdict.<br>Rudolph describes the background/origin of his Tessar in the patent. You can believe what he said, or point out that he would have had to claim it was an original invention else he and his employer would not have been awarded a lucrative patent.
  32. @QG
    Well, I will only respond to
    Did you know that the original Biotar (i.e. not the lens Zeiss East branded Biotar, to avoid the Planar name) is not a derivative of the Double-Gauss Planar, but yet another elaboration of the triplet?​
    We've argued this one out too many times, and I didn't 'drag in' the Biotar, it was in the link given elsewhere, anyway.
    The Biotar that came out on the Contax S, from "Zeiss East" was the same lens as they had provided for the Exakta and Praktiflex BEFORE WWII, so it is hardly accurate to suggest that they so 'branded' it so to "avoid the Planar name".
    At the time the Biotar was produced for the Contax S, was Zeiss Oberkochen making any Planars, at least for 35mm format?.
    I thought in our old controversy you were the one arguing for the Biotar being "derivative" and I was the one arguing for its relative independence?
  33. JDM,<br>O.k., o.k.! ;-)<br>Was interesting to note that the Biotar first appeared as a triplet derivative, was it not?
  34. QG
    O.k., o.k.! ;-)
    Yes, but the later Biotar (1939 and 1948) I'm concerned with most directly from my interests in crummy old East German cameras certainly is a double Gauss, wouldn't you say?
    Actually, in what we call the Culture Historical paradigm in archaeology (Americanist archaeology from the 1920s to the 1960s), one of the primary tasks of the archaeological technician was to precisely identify what we've called 'families' here in the development of what was called "material culture". I am not part of that paradigm anymore, but I was trained in it, and tend to see the physical similarities as hints to derivation (as you argue for the Tessar connections above). Of course, in most archaeology, we are very fortunate not to have either historical records, or most particularly patent applications in which people put forward their case for their own interpretation. ;)
    In Highland Burma (link to author), to summarize it grossly, every time somebody important in the system dies, there are funeral orations in which each relative tries to assert their own claims to kin closeness. In the end, some win and some lose.
    Are our histories always so different from this? :)
  35. Amazing! We've gone from an educational dissertation on lens design, evolved through an anticipated slightly heated discussion on the finer points, brought Browning shotguns into the picture, and have sidled in the " Culture Historical paradigm in archaeology". It's this kind of stuff that brings me back to this Forum; keep it up, fellas!
  36. JDM,<br>Yes, the later Biotar is a Double-Gauss lens.<br>A thing that is making things a bit harder is that names were given to things, and reused for other things, not necessarily related, later. The Biotar is an example. The Aviogon derived Biogon another.<br>Other things evolved into something that is easily recognized, though the first examples that were given the name don't look much like what we know as such (Sonnar, for instance). Then there are those possibly converging lines of evolution, the Tessar could be an example of that.<br>From the moment that computers were put to use to calculate lenses, design families have disappeared. First a bit. Nowadays as good as completely. New lenses are given tasks such as having a small, light weight group that can be used to focus, or not being too expensive to make, with the computer solving the task of figuring out how to build a lens capable of good performance around such non-optical demands.<br><br>In highland Burma, people may lay claim to kinship to achieve political status. I don't know how that would transferto/be recognizable in the history of lens design, apart from having to claim that some solution is unique to be awarded a patent.<br>But be that as it may, the interesting bits are those about the different directions designers took when trying to solve the same problems, resulting in sometimes very similar, sometimes quite distinct lens families.
  37. I think we should start a new thread and pound out the Xenar, the Elmar and the Tessar. Themes and variations etc !!
    Heres a link and it is more Zeiss centric. Not a lot of new information but an interesting link none the same!!"

    Lots of different lenses discussed!!
  38. Not only did I get a long and entertaining discussion on the history of lens design but I but I learned a new emoticon from JDM which was ;-). He was winking throughout the whole discussion. I had to look it up.
  39. Well, I was winking at least partly because the emoticon for irony, ".~" is so rare and usually unrecognized. :)
  40. The Kingslake book is one of the standard references, and is well documented. It's good to read other source too of coursse, but I would certainly include Kingslake in any discussion.
    Kent in SD
  41. new thread?: "Xenar, the Elmar and the Tessar. Themes and variations"
    Go to it, I'll watch as my stings heal. :|
    "There was this funny papery looking globe in the tree, so I poked with my stick to see what it was."​
  42. Rudolf Kingslake was a London borned optical designer, he got a MS degree from Imperial College of Science and Technology, under Alexander Eugen Conrady,latter maried Conrady's daugther, and edited Conrady's manuscript, published a two volume book on optical design.
    Kingslake was invited to USA to teach at Rochester University, in 1937 he became the head of the opticial design department of Eastman Kodak.
    Kingslake clearly has a british background, yet his opinions on lens design is not biased
    The section on Carl Zeiss Tessar is listed under Chapter 6 under the title "The First Anastigmats", Section IV The Unar and Tessar. While the Cooke triplet is listed in Chapter 7
    "The Triplet Lens and its modifications"
    Clearly, from historic development perspective, Tessar lens follow the Anastimats Unar lens line and not the Cooke Triplet line.
    The sequence of historical development is as follow:
    1)In 1890-1893 Paul Rudolph of Zeiss invented several variants of 4 element 2 group Zeiss
    Anastigmats, with front and rear cement doublets.
    2)In 1899, Paul Rudolph separated the cemented doublets in his Zeiss Anastigmats with air spaces into 4 element 4 group lens, the Unar. The Unar was a good design, but Ruldolph restored the cemented doublet of his Anastigmats but retain the air space, in other words, he kept the air spaced two front element of Unar, but replaced the air space of Unar’s 2 rear elemnts into a cementd
    Doublet, and Carl Zeiss Tessar of 1902 was born, it was a f/6.3 Tessar
    For derivatives of Cooke Triplets, Kingslake listed Heliar by Hartings in 1902, Ernostars, and Zeiss Sonnar, Leitz Hektor, Thambar, Leitz Elmar, Elmarit
    In other words: Carl Zeiss Tessar iss decendent of Zeiss Anastigmat-Unar
    Leitz Elmar is a descendent of Cooke Triplet
  43. In simpler terms, Paul Rudolph created the wonderful Carl Zeiss tessar by combining the front
    elements of his Zeiss Unar lens with the real doublet of his Zeiss Anastigmat.
  44. From geometric configuration, the Tessar has very narrow 1st airspace
    For instance, 1907 Paul Rudolph Tessar 50mm lens has first element thickess 3.100, first air space 1.700
    While Cooke triplet has rather thick 1st airspace (triplet us pat. 2731884)
    first glass element 6.2500
    first air space 11.790
    Tessar lens always has its aperture stop placed at the 2nd airspace, the 1st airspace is too narrow for aperture stop
    On the other hand, Leitz Elmar has quite thick airspace, able to accomodate aperture stop
    at first airspace.
    Reference: Warren Smith: Modern Lens Design
  45. JDM, the next time you and Q.G. get started in one of these threads, I'm gonna throw the both of you into the same room and sell tickets. Now, I'm gonna be late for work.
  46. While it is possible for the Tessar to have been developed from the Triplet, as Martin says this was not the way the design evolved and that evolution was sufficiently inventive for a Tessar Patent to have been granted. Zeiss and others produced many new lens designs but where Zeiss was unique was in the development of novel types of glass e.g. the barium crowns (in collaboration with Schott). This enabled Zeiss and others to develop the new lens designs. The front achromat of the Zeiss Anastigmat was 'old' glass and the rear achromat was 'new' glass. Ultimately the Tessar was formed by splitting the front achromat of this Anastigmat (what a mouthfull!). This provided two additional two glass-air interfaces for the designer to play with which, it appears, made a big difference.
  47. evolution was sufficiently inventive for a Tessar Patent to have been granted​
    But see QG above on the issues of how patent claims are made.
    There was once a patent on the 'idea' of the early automobile too (Wiki on Selden patents & Henry Ford), for example.
    The simple physical similarity is still (even with written records) a better guide to historical connections than claims made by inventors about where they "got the idea".
  48. Hmmm, yes, agreed JDM. It's inconcievable that Rudolph did not know about the triplet and who knows what actually went on inside his 'little grey cells'? But of course he worked for a company (Zeiss) that (like all companies) would present the narrative to suit its purposes (Patents, marketing, lens sales, etc.). It would suit Zeiss for the whole development to be a Zeiss development. But what Zeiss unquestionably did (with Schott) was develop the new glasses that were needed in the Tessar design.
  49. The simple physical similarity is still (even with written records) a better guide to historical connections than claims made by inventors about where they "got the idea".​
    Why should I believe that?
    "I'm a liar so everyone lies," I'm an PhD archaeologist and that's what we believe" and appeals to greedy capitalists are not arguments and won't convince. Documentation that will allow us to estimate the probablility that what actually happened and what was reported are strongly discordant will convince. Show us your data and calculations.
  50. Because people, at their best, make their own case.
    "I'm a liar so everyone lies," I'm an PhD archaeologist and that's what we believe" and appeals to greedy capitalists are not arguments and won't convince.​
    That's offensive, Dan.
  51. No need to get into a fight over this.<br>As you do know, Dan, there is such a thing as written documentation, and there is the question of whether that is reliable. That an account seems to fit is just as unreliable as the physical similarity. Neither are proof, unless corroborated. And a book recounting the tale once told by someone is a secondary source, not corroboration.<br>I think we will never know. All we can do is choose what we want to believe.
  52. JDM, where's your data?
    In this case, the lab notebooks will do. It that offends, sorry.
  53. lab notebooks? It's the demeaning references to my profession and in effect calling me a liar that is offensive, as you surely meant it to be. Go play with yourself, you're not fit for company.
    If you knew anything at all about art history or archaeology of any flavor, you'd understand what I'm talking about. I don't have to recapitulate several centuries of well-established methods just because you're not calm in your mind.
    Now mount the Triplet and Tessar images so you can see one with the left eye and one with the right eye. blink back and forth.....
  54. Is it safe to come out yet? Guys, it's like I used to say while I was still at my last job, "They don't pay me enough to take this personal."
  55. Actually H.Denis Taylor's orginal Cooke triplet patent did include a four element lens, alas, with a doublet in the CENTER.
    If his patent included a rear doublet, then he would have included Tessar type lens in Cooke triplet. But
    he didnt and missed out. Hence the talk about Tessar derived from Cooke triplet is completely superficial and without merit.
    Cooke triplet due to its strong elements, particular the very strong negative center element is much more
    difficult to manufacture, in early days, the possition of the center element of Cooke triplet was determined by trial and error, then glued; many manufacturer rather made 4 element lens instead of Cooke triplet. Tessar has no such disadvantage, it is a superior design.
    The following lenses are all Tessar type:Agfa Solinar, Voigtlander Skopar, Dallmeyer Dalmac,Perfac,Kodak Ektar, Rodenstock Ysar, Schneider Xenar, Wollensack Raptar.
    Derivative of Tessar includes: Zeiss Biotar
  56. The popular practice of lens illustration only provide the lens diagram, this practice leads to
    wide spread miscoception, as if a lens is defined by how many group of glassses, how many airspaces , hence this lead people easily believes in the mind that Cooke triplet and Tessar both
    obviously has three group of lenses and two airspace, thus they must belongs to the same family.
    In actual matter of fact, a valid lens patent includes a lot more detail, for example in the 1907 Paul Rudolph Tessar patent, includes data for various radius of the elements, their thickness
    four specific glass type (three types of crown glass and one flint), the refractive indices of these material, the V numbers etc about 27 variables. Changing any one of them involved laborious
    manual calculation with 8 figure logarithm table, to check the focal length, and various aberrations to see where they meet the performance specification and manufacture tolerance,
    a complete lens design in those days usual took half a year's calculation.
    It is not as simple as x group y elements.
    There are more than eighty Cooke triplet type patents, the patents are all in the detail choice of parameters.
  57. [​IMG]
    This is Carl Zeiss Merte patent for F2.8 Tessar,
    The difference: the cemented doublet at front, and the use of high refractive index glasses.
  58. JDM, you made an argument that is, at its heart, statistical. You asserted that the probability that claims in patents reflect the process by which the patented item was developed is low. Surely you have data to support the assertion.
    This has nothing to do with art historians' or archaeologists' or liars' practice, it has to do with whether claims in patents systematically misrepresent what was actually done. In the case of the Tessar's design, the computers' instructions and worksheets contain the answer.
    Oh, and by the way, when I was a young grad student digital computers weren't generally available. I worked my way through grad school as a research assistant, did large computations on electro-mechanical calculators. I've been a computer myself. So much for the myth that computers were all attractive young women.
  59. "In the case of the Tessar's design, the computers' instructions and worksheets contain the answer."

    Too assertive. They may contain an illustration of how something was changed to form something else, that was inspired by seeing yet another something else. A record of how it was avoided to have to begin from scratch.
    Could be. Perhaps not. Who knows?
  60. Martin,<br>Thicknesses, radii and such aren't that important for the question whether a lens is part of the same family or not. Important is why a lens was made the way it is, what problem was tackled and what direction was taken to get to the solution. The triplet appears to have been aspired by the thing about Petzval sums and the Petzval theorem not saying anything about thicknesss and distances, providing a way to create rather good lenses by subdividing a glass blank and spacing the parts thus created. How the thicknesses were tweaked, radii changed, spacings altered, orderes changed is part of what was done to make the lenses based on that idea better ones.
  61. I'm a physicist and have written a number of patent applications. An application does not have to 'reflect the process' by which the invention was developed. An application has to describe the thing and show how it is 'inventive over the prior art'. To achieve this its normal to describe the 'prior art' and then state the 'inventive step' for which a patent is being applied for. This 'inventive step' and any other essential details form Claim 1. All inventions have to actually work so you also have 'embodiments' i.e. practical examples of the invention. In the case of a lens it would be certain radii, glass etc. leading to certain (acceptable) aberrations etc. It's not necessary to describe in an application how you actually arrived at the invention.
    Boy, it's much more interesting talking about lenses than it is talking about patents...
  62. Back in the original post that seems aeons ago, JDM wrote:
    I am always amazed at how well Wikipedia does with non-political/non-controversial subjects​
    I agree about how well Wikipedia does. But with the devolution of this thread into acrimony, the original hypothesis of "non-controversial" as to the subject of lens anatomy now appears, lamentably, to be proven inoperative!
  63. @Dave,
    My thoughts exactly.
    I will also repeat, and take it as having been proved here, what I said in the third paragraph of the OP:
    The history of photography and optics is no more clear of local prejudice than is any other branch of history. Cox, as his titles show, is definitely a Briton. So naturally enough, Cox tends to see the history of optics in fairly British terms. This is not so much wrong as it is a little provincial, but the Germans, Americans, French and citizens from other places with 19th and early 20th c. optics industries are just as provincial in their own ways.​
    I wasn't surprised that there were different views, but I was surprised at how vehement those views have proved to be. Nor did I expect the claims for inerrancy for certain texts.
  64. Bertele worked at Ernemann before Zeiss. Bertele's Zeiss Sonnar is basically Bertele's Ernostar with the 2nd and 3rd element filled in with a glass of low-refractive index to form a triplet. This was to increase transmission of light by eliminating air/glass surfaces. With the advent of multi-coated optics, the C-Sonnar design went back to the Ernostar layout, as the elimination of air glass surfaces is not as critical.

    The interesting thing about the Sonnar: the front section is a Telephoto lens with magnification of about 2.5x the overall focal length, and the rear section (triplet, doublet, or single element) is about the same focal length as the overall lens. Spacing between the front and rear sections is close to provide appropriate spacing, giving the compact size as well as the pronounced focus shift.
  65. Taylor's original thinking was along this line:
    1) Take a positive lens and a negative lens of equal power, put them in contact, the power and Petzval sum would be zero
    2) Seperate the two lenses, the resulting lens would have a positive power, but maintain a zero Petzval sum. but with horroble abberation due to non symmetry.
    3) In order to make this lens symmetrical , he suggested to split the positive lens into to two halves, and place them one on each side of the negative element, thus invented Cooke triplet
    The most important aspect of Taylor's design is to split one lens, and put it separately
    one one each side of negative lens.
    To split a triplet thus obtained by again replace the rear element with an achromat doublet(to make a Tessar) would violate Taylor's original idea, which was to SPLIT APART a doublet into two elements, then split one of the element (not into doublet) , but into two separate elements, place one on each side.
    Key words: "pull apart", split one lens into TWO WIDELY SEPERATED LENSES.
  66. There is one important historical fact: It was Zeiss's Schott Glass work that invented several new type of high reflective index barium crown glass, which permit Carl Zeiss to patent several anastigmat lenses composed of what they termed as "New achromat doublet, from high index barium crown with low index flint".
    In other words, the "New achromat " doublet at the rear of Tessar lens was solidly in Zeiss patent territory.
  67. It would not "violate Taylor's original idea", Martin, but work with it, seeing what can be done to make what you get using Taylor's idea better.
    An important distinction, the first suggesting that anything not quite equal to what Taylor did being quite something else, the latter that it would be a tweak of the same.
    And the Tessar and other elaborations are just that: examples of how the original idea could be taken as a starting point and be improved.

    I think it would be historically more acurate to say that the idea did not begin with joining two lenses to reduce the Petval sum, but was born from the notion that ' Petzval' would permit splitting a block of glass any way you want as long as you use all of the resulting parts, because only the radii matter, not the distances.
    Your numbers 1) and 2) are an example of how that could be done splitting a block in two.
    And combined with your 3) show that the original idea is not "violated", but that there is ample room in the original idea for better ways of doing the same. Split in two the results are still no good, so split the block in three and see what you can do with that. The Tessar and other variants do the same, take it a step further. So no more a violation than what Taylor himself did originally.

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