0.8 change in f stop: what's the big deal?

[jean_marie_dederen]

<p>Reading up on the differences between the summaron 35/2.8 and 3.5 revealed two opposing positions: some say the difference is visible whilst others seem convinced there isn't much beyond the fact that the former behaves better wide open. The earlier 3.5 versions at least look different from the 2.8 (but share the same general lens design formula). The <em><strong>final screwmount version </strong></em>of the 3.5 looks and handles the same as the 2.8; they are contemporaries (late 1950's), have the same lens formula and perhaps even the same glass and coating. How relevant then was the 0.8 lens stop difference? How was it is achieved? And what was the objective? Phrased differently: the 2.8 is known to be a very special lens, a great achiever. Why woukd the final screwmount version - which appears to be identical - not share in the fame of the 2.8?</p>

[aplumpton]

<p>Erwin Puts (pp 108, 109 of his web book) explains the performance differences between the two optics, each of double Gauss design. He refers to the original mid 1940s design of the Summaron f3.5 and the late 1950s upgrading of the f2.8 model. He doesn't mention whether the f3.5 design was upgraded or not in the 1950s. Having the same optical formula doesn't mean that the glass elements of the optic are of the same composition or even have an identical shape/dimensions. </p>

<p>http://www.furnfeather.net/books/pdf/llcforweb.pdf</p>

[jean_marie_dederen]

<p>True Arthur. What intrigues me is that the final 3,5 screwmount version is identical to the 2.8. Was Leitz trying to secure the continued sale of the 3.5 by dressing it up as a 2.8? Or trying to establish the 'new look' of the 2.8? And how different were they really in design and (perceived or 'real') performance? The 2.8 was obviously meant to replace the 3.5; then why bother with revamping its looks? Seemingly this 3.5 screwmount was only produced for two years: 1958, 1960. I believe its was named the SOONC-MT 11305 and meant for the M2. </p>

[jean_marie_dederen]

<p>The difference between these two summarons is definitely not in the order of say the difference between the nikkor 28/2.8 and 28/2, the design and performance of which are like heaven and earth.</p>

[User_502260]

<p>Are you saying that the 28/2.8 AIS Nikkor is not as good as the 28/2 Nikkor or that the 28/2.8 AI Nikkor is not as good as the 28/2 Nikkor?</p>

[john_stockdale2]

<p>I had a Summaron 35/3.5 (M mount) and it was sharp in the centre but quite disappointing at the edge, even with 400 film and hand holding.</p>

[aplumpton]

<p>Jean-Marie, I am also not familar with the Nikkor f2.8 and f2 models, but I do think that designing a 35mm f2 lens is a more complicated task than an f3.5 or f2.8 lens, just as the f1.4 is different and more difficult to design/produce than an f2. The M mount 35mm f1.4 (non-aspherical) is no slouch, but it was apparently not as good a the Summicron at most equivalent f stops and its wide open performance showed a lot of aberrations such as coma (I know of the performance of those two, having borrowed or owned them at one point).</p>

<p><em>(Si vous avez eu la chance de lire "Chasseur d'Images" dans les années 80 ou 90, vous auriez vu qu'ils ont presenté des essais sur les objectifs et quelques optiques supposement inférieures à Leitz - par exemple les Yashinon de Yashica - ont recolté des felicitations pour les excellent optiques de 28mm f2.8 et de 21mm f3.5, et qui ont surpassé plusieurs objectifs équivalents d'Europe) </em></p>

[james_elwing]

<p>How was the 3.5 & 2.8 'identical'? I assume it looked similar. Certainly the M versions with 'spectacles' for the M3 are easy to tell apart.</p>

[jean_marie_dederen]

<p>Sorry for delaying my reply; price paid for living worlds apart.<br>

Jeff - They have heir distinctive merits (both are flareproof and the f2 has an incredible resolution); the point I was trying to make was that I can see the difference in the nikkors design, but not in the summarons (especially the final screwmount 3.5).<br>

I must admit that I am a total stranger in leicaland, and am considering buying my first lens: one of the two summarons; hence my inquiry. <br>

Arthur - I will trace Les chasseurs; much obliged for the reference, sounds like a book I would enjoy reading very much. I really do appreciate and enjoy your very informative inputs on this website.</p>

 

[jean_marie_dederen]

<p>Oeps, it's a journal; thanks anyway Arthur.</p>

[james_elwing]

<p>They were designed 10 years apart at the dawn of the computer age, so the 2.8 would have many more computer calculations to finesse the design. It is a modern lens. </p>

[jean_marie_dederen]

<p>James - That's what it looks like, but on closer scrutiny both the final version of the 3.5 screwmount and 'new' 2.8 appeared in 1958. Both have 6 elements in 4 group designs. They almost look identical. Just wondering how similar they really are.</p>

[james_elwing]

<p>Erwin Puts does not mention any recomputation of the 3.5 from its 1949 design, and it wouldn't make sense anyway; why would they bother. He says the f2.8 had an edge but the 2 lenses were both quite good by f8.<br>

There were at least 4 versions, the SM with separate viewfinder, M with separate viewfinder for M3, M with goggles for M3, and M for M2 bringing up correct 35mm frame.</p>

[jean_marie_dederen]

James - You are right. Changing the 3.5 version optically in its final stage of production whilst introducing its replacement (2.8) does not make sense. The last screwmount version of the 3.5 I keep on referring to was marketed as 'the M2 version'. Seemingly it was leitz's intention to discontinue the 3.5 and replace it by the 2.8. By using the the 'new look' of the 2.8 (for the construction of the final 3.5 version) they could get rid of their old glass easier and faster. This particular version of the 3.5 ( SOONC-MT 11305; 1958) was only built for a short while; it is not clear how many were produced as production figures combine different 3.5 versions. The diference in performance with the 2.8 is probably minimal.

[carlo_innocenti]

<p>Just a minor note: the numer of stops between 2.8 and 3.5 is 0.64, not 0.8 .<br>

2 log(3.5/2.8) / log(2) = 0.643856...</p>

[Troll]

<p>Modern Photography tests of the three 35mm lenses (published in the same issue) indicated that there was very little difference in performance between the 2.0 and the 2.8, while the 3.5 was significantly poorer.<br>

My own LTM 3.5 leaves a lot to be desired. I think it is more a matter of micro contrast than resolution. Definitely an improvement over the 35mm Elmar, however. </p>

[Rob F.]

<blockquote>

<p>Having the same optical formula doesn't mean that the glass elements of the optic are of the same composition or even have an identical shape/dimensions.</p>

 

</blockquote>

<p>I've always used "formula" in the context of lenses to mean the specific glasses, curvatures, spacing, and number of elements. The specific design of a specific lens. I take it that "formula" is being used here in a general way to refer to a general class of lenses, such as Triplet or Double Gauss.</p>

[jean_marie_dederen]

<p>Just found out that both summaron f3.5 and f2.8 used the Gauss formula with 6 elements in four groups: front and rear singlets and cemented pairs on both sides of the lens centre. The 2.8 is said to have been produced with newer glass and slightly adjustment spacing of the elements to produce greater light gathering capability and slightly better performance at wider apertures. I have read elsewhere that there isn't much difference between the two types. (There shouldn't be if they used a similar lens formula!)</p>