If there are no perfect lenses then there are at least those that come close. The Carl Zeiss Sonnar T* 2.8/85mm for Contax-Yashica mount is one of those. This is a film-era lens designed for Contax SLRs. For more details, read my previous article, in which I sing the praises of this lens line as a whole. Here I will share photos from this particular optic.
Though the Contax Zeiss lenses are well-loved, you don't read much about this 85mm model, no doubt because the maximum aperture of f/2.8 seems inadequate. Why buy this lens when there are so many other 85mm focal length options? No doubt your camera system has at least one such lens, native to your mount. Perhaps it is f/1.8 or even f/1.4. So why choose a slower lens that also requires manual operation?
Overview
Here's the lens on my Lumix S5. I've added an after-market metal lens hood. The adapter is an inexpensive K&F Concept unit. The lens itself is small for a portrait focal length. At only 220g and 46mm deep, one can mistake this for a fast fifty. Indeed the Planar 50/1.4 is only 5mm shallower and weighs 70g more. This is the benefit of the relatively slow f/2.8 aperture.
This classic Sonnar design uses only five lens elements in four groups, which, if one is to believe contemporary lens design philosophy, is altogether too simple to achieve greatness.
Carl Zeiss offered the Planar T* 1.4/85 for an extra two stops of light. Certainly on film this is a compelling option. But mounted on a digital mirrorless camera with seemingly endless ISO ranges, light is no longer an issue. What then of bokeh? Here the Sonnar acquits itself well. The bokeh is lovely, circular, and smooth. It is simply not necessary to have a wider aperture, despite what YouTube pundits might tell you.
Another reason to have a wide aperture is to get a thin depth of field. There is certainly a mania for this look in contemporary photography. But at a longer focal length like 85mm, it's almost impossible to have a face fully in focus at less than f/2.8. In fact, f/4 is often better. This way you can be reassured that not only the nose of your subject will be sharp.
Finally, people prefer a faster aperture since lenses gain optical quality when stopped down. For many brands this means that the open aperture is compromised by haze, low contrast, or softness, to the point where it is usable only as a special effect.
Zeiss bucks that trend. If they need to make a lens slow, they will. But you can be sure that the open aperture is usable. My photos included here demonstrate the image quality at f/2.8. (Unfortunately I am not much of a people photographer, so if you are more interested in portraits, you will need to seek out other examples.)
MTF chart
To get an idea of how the lens will perform, we can check out the MTF charts provided on the official Zeiss data sheet. Note that these are actual measurements, not theoretical numbers. Zeiss is the only company to provide this data direct from the engineers, unfiltered through marketing expectations. The fact that they maintain this database long after the lenses have left production is another testament to their integrity.
Each data sheet has MTF charts for the lens wide open and stopped down to f/5.6. The curves from top to bottom represent spatial frequencies of 10, 20, and 40 line pairs per mm. Simply put, we can interpret the top lines as indicating contrast and the bottom lines as sharpness. In each case, the closer together the solid and dotted lines, the "nicer" the image, smoother the bokeh, flatter the field, etc. You can actually tell a great deal from an MTF chart without ever using a lens.
It's obvious that the Sonnar 85/2.8 has incredible micro-contrast from wide open, almost indistinguishable with the quality at f/5.6. Indeed, this is a defining feature of the Zeiss family, along with a naturalistic colour rendering. This leads some to claim the lens has too much contrast to use for portraiture, preferring the Planar 85/1.4. But with digital processing there's no such thing as too much contrast. I'd rather be in the position of reducing contrast in post than adding it artificially.
In terms of sharpness, the Sonnar puts in good results almost all the way across the frame, which is certainly not what one might expect at f/2.8. This improves to "very good" and is entirely consistent by f/5.6. Besides increasing DOF, the only reason to stop down is to improve border performance, which is only really an issue for landscape photography.
The distortion chart shows a 1.5% maximum value. While low, this wouldn't be the perfect lens for architectural photography. I might instead choose the Planar 2/100mm which has one-third this amount. But for general photography, that figure is unnoticeable.
All of these theoretical results are borne out in actual shooting. Sharp, contrasty images result every time. You can shoot wide open without worrying about any negative effects on the image quality. Apparently the earlier AE model flares easily, a feature film-makers might desire for that vintage look. My MM copy doesn't seem to flare at all.
So is this the perfect lens? For many people, yes. For me, there is one Achilles heel. The close-focus distance is one meter. Since my subjects are more often animals, flowers, or architectural details, I prefer a close focusing lens. For the leaf photo I cropped the file about 50% to get this enlargement.
A search will turn up other positive reviews of this lens, for example here and here. You can purchase a copy for about €300-400 on the used market (the MM variant having a premium over the AE).
Family resemblances
A similar optic was available for Rollei cameras in the QBM mount. This has a different lens formula but all reports are similarly positive. Read one review and another.
Also similar, if not identical, is the Carl Zeiss T* 2.8/90 produced in the mid-1990s for the Contax G system. The significant disadvantage of that lens is the lack of a focus ring, as the original system supported only auto-focus from the camera itself. There is no adapter for Lumix that restores this functionality, but if you are on a Sony system you might have more luck. Read one review and another.
A word about the photos
These shots were processed in Affinity Photo with my default settings. This applies a slight exposure S-curve and a clarity boost. I cropped but otherwise did very minor retouching. Some have a minor film LUT applied. The leaf was actually desaturated slightly. The rose is the only photo with a significant "look" applied. The snapshot of the camera is from my phone.
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