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Olympus OM 85mm f2: the OM sonnar

Jim Baker , Apr 13, 2012; 10:12 a.m.

I have been doing a bit of research on the design of this lens. It is a 1920's design, one of the Ernostars designed by Ludwig Bertele. The main characteristic of this asymmetrical design is the three large front elements. He then went on to design the Sonnar in which two of these elements are replaced by a cemented triplet. In the days before lens coatings this increased contrast (by removing glass-air surfaces) while allowing control of high order aberrations. Once coatings were developed, this was not so much of an advantage. The OM 85mm is quite like the current Zeiss ZM 50mm f1.5 Sonnar in that they both have the three separate Ernostar-like front elements. The rear groups are different: a cemented triplet for the Zeiss and a cemented doublet for the OM . It appears that even Zeiss have decided that the front cemented triplet is no longer necessary but I imagine their rear cemented triplet (as opposed to the cemented doublet of the OM) is necessary for Zeiss to control the high aperture aberrations. The OM 85mm is very like the current MS Optical 50mm f1.3 Sonnar (i.e. 5 elements in 4 groups). It appears that lens manufacturers are reluctant to revive the 'Ernostar' name, even though it is historically accurate, preferring to keep the name 'Sonnar'. Both these Sonnars are noted for the sonnar 'look' in particular a smooth bokeh. The Zeiss Sonnar suffers from focus shift i.e. a change of focus with aperture. Zeiss state that this problem is intrinsic to sonnar designs which do not have floating elements so the only way to overcome the problem with their lens is to compensate in some way at the time of taking the photo. Several of the Olympus OM lenses (e.g the 85mm) are based on German designs but Olympus, rather than simply copying them, seem to have tried to improve on them. One point before discussing the design: why 85mm? It's not possible to design a 50mm sonnar for an SLR -there's not enough room for a mirror behind the lens. Obviously 85mm is OK. Olympus designed their 85mm with floating elements in order to control high order spherical aberrations at close focussing distances. Using a ruler to measure the axial movements of the lens, it's apparent that the lens moves as a unit when focussing from 0.85mm to about 10m but the distance between the front and rear groups increases by about 0.5mm as the lens is focussed from 10m to infinity. I have never noticed any focus shift with my OM 85mm so it appears that this correction has done the trick. Olympus managed to patent this feature. In the same patent they explain that flotaing elements also have the advantage of controlling aberrations at full aperture: in particular coma becomes more symmetrical. They claim therefore that the soft focus effect at full aperture is particularly pleasing i.e. it can be particularly good for soft focus full aperture portraits.
My OM 85mm is indeed a little soft at full aperture; its particularly sharp at f2.8 and only really recovers this sharpness by f8. I tend to use it from f2.8-f11 and I've never particularly noticed the sharpness (or relative lack of it) in a print. What I do notice is a particularly smooth bokeh. Accorrding to current usage of the name, it really does deserve to be called 'the OM Sonnar'.

Responses

Matthew Newton , Apr 13, 2012; 11:21 a.m.

Interesting information. One thing to keep in mind however, there are two optically different versions of the 85/2. The original single coated version, serial numbers up through 115,000 use a 6 element in 4 group design. The later multicoated versions (serial numbers over 115,000) used a 5 element in 4 group design. Instead of the 2nd group (starting from the front of the lens) being a cemented doublet, it was changed to a single element, same exterior shape/dimensions. Also the handful of lenses tests that actually compare the first to second optical versions of the lens, plus a lot of anecdotal evidence says that the change resulted in the 5/4 e/g later version to be significantly sharper than the first version of the lens.
I have the later version (actually the final version, which are serial numbers over 200,000 which have a newer multicoating that Olympus Zuiko was using in the last versions of their OM lenses before production ceased). In my experience mind is quite sharp even wide open at f/2. It is actually probably my sharpest OM lens wide open and just gets better stopping down. The only lens I have that might be better for center sharpness is my zuiko 24/2.8, but the 85/2 deffinitely exceeds it in corner sharpness wide open (and that is f/2 compared to f/2.8). It does have beautiful Bokeh.

Craig Dickson , Apr 13, 2012; 02:04 p.m.

I don't have the 85mm f/2, but I do have the 100mm f/2.8 (probably fairly early: it's marked E.Zuiko Auto-T, sn 154xxx). I know it's a different design (5 elements in 5 groups), but how would you compare it to the 85mm f/2 in terms of sharpness and bokeh?

Jim Baker , Apr 14, 2012; 08:16 a.m.

Yes, Matthew, you are right, the original lens was 6 elements in 4 groups.It's pure speculation on my part but my guess is that Olympus improved the original design, in particular at full aperture, and found they did not need the doublet in the front group. The original 'controlled softness' at full aperture fell by the wayside. I also have the later version and it seems sharp enough at all apertures, although if you look closely enough, its best at f2.8. I choose the lens if I want to have a nice blurred background. It really excels in that department.
I don't have the 100mm f2.8, Craig. It's too close in focal length to my 85mm lens. I came across its Olympus patent when I was carrying out my research (US 4114992, the 85mm patent is US 3848972). Olympus say in the title its an Ernostar: 'Variant Ernostar Type Long Focus Lens System'. Their improvement is an extra element in the front group. From what I've read about it on the net, it's a well regarded lens. My guess is that it would have a similar performance to the 85mm lens. Olympus certainly seemed to have liked the design. Their 100mm, 135mm and 180mm (all f2.8) lenses are all the same design!

Ingemar Lampa , Apr 15, 2012; 12:37 p.m.

Very interesting indeed.

I have the older, single coated, lens. Judging on quite unscientific experience, it does seem to slightly change focus with aperture. At least in my hands. Maybe this is what they improved for the later versions.

At any rate, correctly handled, it is a fantastic piece of glass an can still be found for reasonable money. Not so with the 100mm/F2.0 - or my dream lens - the 90mm/F2.0 Macro.

I did mention this before on this board, but it is worth repeating I suppose: According to Maitani-san himself, all the F2.0 lenses regardless of focal length were in his opinion the pinnacle of what Olympus/Zuiko produced and quite different from the slower lenses of the same focal length. That is different, not necessarily "better", but different meaning you get other characteristics. His favourites were the 21, 24 and 28mm/F2.0. He said he "skipped" the 35 and 40mm/F2.0 (personally I love my 35mm/F2.0). The tele lenses were not his cup of (Japanese green) tea apparently!

Jim Baker , Apr 16, 2012; 05:40 a.m.

Ingemar: there are difference between lenses of the same focal length and not necessarily the f2 versions vs. the rest. Personally I have to resist the temptation to keep buying lenses and I guess the best counter-argument I give myself, if I were to consider starting to buy the f2 lenses, is that only two things would happen: 1) my pictures would not get any better and 2) my kit would get heavier. So far this argument has won out! Maybe a digression into the differences between Olympus lenses in general would take us too far of the current topic so I'll leave it for now.
Craig: there's an interesting comparison of the Olympus 100mm f2.8 vs. the f2 version on the www.marcocavina.com website, under Articoli, test no.7. It's in Italian so some of the text is 'lost in translation' but you get the gist of it. Also there are many test shots to look at. He rates the 100mm f2.8 very highly indeed against the f2 version.

Matthew Newton , Apr 16, 2012; 08:32 a.m.

I have a late version zuiko 100/2.8 as well as the 85/2. In my opinion at f/2.8 the 85/2 is sharper. However, the 100/2.8 is still a very good lens. Pretty good wide open and very sharp stopped down. No noticable CA at any aperature (at least with 35mm film and 3200dpi scanning on a flat bed).
Personally if I had stuck with film, I probably would have started going for the F/2 lenses. Maybe not the 28/2. I hear it is a fantastic lens...but I have a Sigma 28/1.8 in OM mount! It is a wonderfully sharp lens and very good even wide open. Its bigger than the Zuiko 28mm f/2, but it goes a 1/3rd of a stop faster, and if the zuiko 28/2 is sharper, than it is a darned scalpel, as the sigma is really excellent.
Rather sadly since I am switching to digital (OM-D) I am selling off most of my lenses. I won't be parting with them all. So far I have sold my vivitar series 1 70-210/3.5 and Tamron 28/2.5 for 3rd party lenses and my Zuiko 35/2.8 and 135/3.5. Next I am looking at selling my Sigma 14/3.5 (an extremely rare bird indeed) and sigma 28/1.8 (also very rare). I am going to keep my sigma 70-210/2.8 APO and 400/5.6 APO for super-tele lenses, for the foreseeable future. I am also planning on at least interim keeping my zuiko 100/2.8 as a nice tele with converter on the OM-D. I will also likely sell off my Zuiko 50/1.4 MC. My Zuiko 24/2.8, 50/1.8 MIJ and 85/2 I plan on keeping indeffinitely for use with the single OM-1 body I am also keeping so that I can continue to shoot film from time to time and for me those are the 3 "golden" lenses that make up a complete, if basic kit for film (and I'll probably shoot the 85/2 and 50/1.8 with adapters for awhile, at least until I can get the zuiko 45/1.8 and later the 75/1.8).

Darin Cozine , May 08, 2012; 08:59 p.m.

I have the 85mm f2 with a serial number 212xxx. I must say it is a good lens, I just wish I could live up to it!

Jim Baker , Oct 11, 2012; 08:40 a.m.

I know this thread is no longer active but for the record I'd like to report that MS Optical have just (September 2012) produced a 50mm f1.1 'Sonnetar' lens. The 'Sonnetar' is in fact the same optical construction as their f1.3 Sonnar (which I mentioned above) and of course is the same optical construction as the Olympus 85mm. What is particularly interesting about this new lens is that the rear of the lens has a 'coma adjustment ring' with settings for infinity, 4m, 2m, and 1m. I suspect this adjustment does the same as the Olympus 85mm 'automatic adjustment at close focussing distances' except that it is a manual adjustment. Although MS Optical call it a 'coma adjustment ring' it appears also to correct for spherical aberration, at least that's what it says on the japancamerahunter.com website (they are marketing the lens).

Bill Lynch , Oct 11, 2012; 01:50 p.m.

It would be nice if we could mount that lens on an Olympus OM film camera.

I know... there I go, dreaming again.

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