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

[q.g._de_bakker]

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.

[dan_fromm2]

<p>JDM, where's your data?</p>

<p>In this case, the lab notebooks will do. It that offends, sorry.</p>

[JDMvW]

<p>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.</p>

<p>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.</p>

<p>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.....</p>

 

[Rob_the_waste]

<p>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."</p>

[MTC Photography]

<p>Actually H.Denis Taylor's orginal Cooke triplet patent did include a four element lens, alas, with a doublet in the CENTER.<br /> If his patent included a rear doublet, then he would have included Tessar type lens in Cooke triplet. But<br /> he didnt and missed out. Hence the talk about Tessar derived from Cooke triplet is completely superficial and without merit.</p>

<p>Cooke triplet due to its strong elements, particular the very strong negative center element is much more<br /> 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.</p>

<p>The following lenses are all Tessar type:Agfa Solinar, Voigtlander Skopar, Dallmeyer Dalmac,Perfac,Kodak Ektar, Rodenstock Ysar, Schneider Xenar, Wollensack Raptar.</p>

<p>Derivative of Tessar includes: Zeiss Biotar</p>

[MTC Photography]

<p>The popular practice of lens illustration only provide the lens diagram, this practice leads to<br>

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<br>

obviously has three group of lenses and two airspace, thus they must belongs to the same family.<br>

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<br>

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<br>

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,<br>

a complete lens design in those days usual took half a year's calculation. <br>

It is not as simple as x group y elements.<br>

There are more than eighty Cooke triplet type patents, the patents are all in the detail choice of parameters.<br>

<img src="/photo/17089812&size=lg" alt="" /><img src="http://d6d2h4gfvy8t8.cloudfront.net/17089812-md.jpg" alt="" width="680" height="510" /></p>

[MTC Photography]

<p><img src="http://d6d2h4gfvy8t8.cloudfront.net/17089813-md.jpg" alt="" width="680" height="510" /><br>

This is Carl Zeiss Merte patent for F2.8 Tessar,<br>

The difference: the cemented doublet at front, and the use of high refractive index glasses.</p>

[dan_fromm2]

<p>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.</p>

<p>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.</p>

<p>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.</p>

[q.g._de_bakker]

<i>"In the case of the Tessar's design, the computers' instructions and worksheets contain the answer."</i><br><br>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.<br>Could be. Perhaps not. Who knows?

[q.g._de_bakker]

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.

[jim_baker6]

<p>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.<br>

Boy, it's much more interesting talking about lenses than it is talking about patents... <br>

</p>

[Argenticien]

<p>Back in the original post that seems aeons ago, JDM wrote:</p>

<blockquote>

<p>I am always amazed at how well Wikipedia does with non-political/non-controversial subjects</p>

</blockquote>

<p>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!</p>

[JDMvW]

<p>@Dave,<br /> My thoughts exactly.</p>

<p>I will also repeat, and take it as having been proved here, what I said in the third paragraph of the OP:</p>

<blockquote>

<p>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.</p>

</blockquote>

<p>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.</p>

[Brian1664876441]

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.

[MTC Photography]

<p>Taylor's original thinking was along this line:<br>

1) Take a positive lens and a negative lens of equal power, put them in contact, the power and Petzval sum would be zero<br>

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.<br>

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</p>

<p>The most important aspect of Taylor's design is to split one lens, and put it separately<br>

one one each side of negative lens.</p>

<p>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.</p>

<p>Key words: "pull apart", split one lens into TWO WIDELY SEPERATED LENSES.</p>

<p> </p>

[MTC Photography]

<p>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". <br>

In other words, the "New achromat " doublet at the rear of Tessar lens was solidly in Zeiss patent territory.</p>

<p> </p>

[q.g._de_bakker]

It would not <i>"violate Taylor's original idea"</i>, Martin, but work with it, seeing what can be done to make what you get using Taylor's idea better.<br>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.<br>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.<br><br>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.<br>Your numbers 1) and 2) are an example of how that could be done splitting a block in two.<br>And combined with your 3) show that the original idea is not <i>"violated"</i>, 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.