Zeiss APO Sonnar 135mm f/2 (ZF.2) Review

As written many times before, MTF charts are usually based on close to minimum focusing distance of the lens. Changing focus plane might influence “sharpness” significantly, almost like stopping lens down one or more stops.

Testing lens for medium and infinity distance in a field, is however very tricky, and such tests should be always taken with a grain of salt.

In the following example I would like to show you why this is so tricky and why you should be careful, making any conclusion based on real life shots.

Bellows are two shots taken with two different lenses in en effort to compare sharpness at infinity. Because infinity mark on the lens doesn’t correspond with actual focus plane on neither lens I had to focus using magnification on LCD screen.

Lens A

Lens B

While they both looks acceptably sharp at this size, it is enough to shift the focus for less than 1° and results at pixel level will be compromised. Outside in the direct day light, even using hood loop for LCD makes critical focusing… critically difficult. While closest subjects in the images are over 70m far and further around 100m and that should be well into DOF for those lenses in theory, when looking at pixel level… forget about theory.

Maybe less than 1°caused those differences in 100% crops. Left is lens A, right is lens B.

Critical focus is just one of the problems that can be expected. Focus breathing and related difference in FOV, lighting conditions that keeps changing during test, temperature, humidity and other aspects that can affect visibility at longer distances and many other variables are just some of the reasons why real life tests shouldn’t be taken too seriously, when judging or comparing “sharpness”.

On the other hand, when there is time to repeat enough different tests, there will be good chance to minimize those variables in order to come to conclusion if the lens is rather sharp or not.

Among three lenses that I compared so far – Zeiss, Samyang and Nikkor, only Nikkor stays slightly behind in terms of sharpness at medium to infinity distances and rather in contrast than resolution itself. Adding much more pronounced CA in Nikkor 135/2 AF DC, makes this older design somewhat insufficient for large resolution modern sensors at its widest aperture, but on the other hand, those lenses are mainly portrait lenses and as we would be able to see in one of the following chapters, slight softness wide open is not always bad thing.

Stopping Nikkor down to just f/2.8 significantly improves its sharpness perception, and from f/8 it is hard to tell lenses apart in both resolution and contrast.

When it comes to sharpness differences between Zeiss APO Sonnar 135mm f/2 ZF.2 and Samyang 135mm f/2 ED UMC ZF.2, I have to say that they are field irrelevant IMHO. Zeiss kept slight edge wide open in most of my tests, especially moving further from the center, but that edge is really very thin and resulting sharpness will be much more affected with other things mentioned above (critical focus, visibility conditions, lighting).

As I wrote at the very beginning of this review, Zeiss APO Sonnar 135mm f/2 is one of few lenses that can be used wide open even for landscape shots e.g. without sacrificing much sharpness.

Let’s look at this image e.g.

I made 100% crops from related zones (A,B,C,D) in the large composite image bellow, to show how little differences in sharpness can be observed through the whole aperture range.

You will notice that from f/16 diffraction starts to affect sharpness, but believe me, even f/22 can be used with additional sharpening for very large prints. In this case however, there won’t be many situations, where you will need more than f/5.6 for usual landscape composition and that (and f/4) is at the peak of lens performance anyway.

Bellow is set of comparable images between tested lenses.

Zeiss vs Nikkor at f/2

Zeiss vs Samyang at f/2

Zeiss vs Nikkor at f/2.8

Zeiss vs Samyang at f/2.8

Zeiss vs Nikkor at f/5.6

Zeiss vs Samyang at f/5.6

Original size files of test posted above are in this Flickr collection – https://www.flickr.com/photos/97543230@N02/collections/72157651629343231/ if you wish to explore them more in detail.

This test images were focused at near to infinity distance. While at close distance Zeiss had narrower FOV, at medium and infinity distances it seems that some focus breathing enter the game, because it gets closer to original Samyangs FOV, while Nikkor keeps its real FOV best of the three and become narrower among them (larger magnification).

I am lazy to measure focus breathing because it is not significant, so I am happy just to know about it. It shouldn’t make any difference in a real life shooting though. (It also make sense to get largest magnification possible at close distances while at infinity it shouldn’t matter).

In another of many comparative tests that I did, I tried to compare sharpness at infinity. Here is test image with marked zones.

Bellows are 100% crops compared directly between lenses.

At f/2

At f/2.8

At f/11

Similar pattern can be observed on those images. Zeiss has slight edge wide open and Nikkor lags behind both. Already at f/2.8 Nikkor improves a lot while Zeiss and Samyang are hard to tell apart. At f/11, I really don’t see much differences in terms of sharpness among those three lenses.

At medium distance, I checked only for mid frame sharpness and conclusion is basically same as with long and infinity focus distances.

Zeiss vs Nikkor at f/2

Zeiss vs Samyang at f/2

Zeiss vs Nikkor at f/5.6

Zeiss vs Samyang at f/5.6

To check for diffraction at smallest aperture I compared Zeiss and Samyang at f/22 (Nikkor goes only to f/16)

Zeiss vs Samyang at f/22

There are of course many more 135mm lenses. Together with 50mm and 35mm FL, 135mm is probably most represented focal length for 35mm format and there are often at least two models from most producers.

From those interesting lenses that I would suggest to think about, I picked another three for a simple f/8 landscape shot.

Additional lenses are Sony Zeiss Sonnar T* 135mm f/1.8, amazing lens available only in Sony A mount, even more charismatic and not often mentioned Sony (original Minolta design) 135mm f/2.8 STF (T4.5), and mighty Canon EF 135mm f/2 L USM, living legend among 135mm lenses. To make such a comparison bit more fair, I tested lenses on Sony A7 camera with appropriate adapters. Following image shows 100% crops from respective zones.

In a conclusion, from all tested lenses only Nikkor 135 f/2 AF DC stay a bit behind at wide open apertures, but where Zeiss and Samyang takes a lead is in CA department. Stopped down to f/5.6 and smaller almost erase sharpness differences among tested lenses and at those apertures each one of them will deliver superb results.

Advantage of Zeiss APO Sonnar 135/2 and Samyang 135/2 ED UMC is in their optimization for wide apertures, which makes them attractive alternative for all shots were sharpness across frame is required but light level is rather low. This and brilliant control of CA, makes those two lenses standing above the others by some margin in this respect.

There is of course much more than lens sharpness. In the next chapter we will take look at flare resistance and bokeh.

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