PHOTOOG Photography writings by Olivier Giroux


Carl Zeiss 1.5/50 C Sonnar T* ZM Review

The 50mm C Sonnar ZM is a very unique option for a normal lens. In a nutshell this lens looks and draws as if were a compressed version of the 85mm Planar ZF, in ZM mount. The Sonnar is unusually compact even for its focal length and speed class, but costs far less than Leica’s more modern aspherical lens of similar specifications. There are some well-known issues with this lens however, which should dampen the enthusiasm of many.

The designation “Sonnar” is most typically found on moderate telephoto lenses from Carl Zeiss, in the range of 85mm to 135mm. In this case it applies to a normal lens because its construction is fundamentally similar to that of moderate telephotos, a design choice that gives the Sonnar its unusually small size. More specifically the high magnification in the front groups is not balanced with symmetrical power in the rear groups, permitting the barrel to be shorter than what is natural for the focal length.

Today I am an at an early stage of experience with the Leica M9 and feel the desire to get faster lenses quite keenly. This Sonnar has such universal appeal on paper that I quickly settled on it for my first taste of a high speed 50mm M lens. Roger and his team at LensRentals.Com kindly agreed to send me a beautiful copy of the lens for this review.


This 50mm ZM is the smallest lens I have used thus far. It is shorter but slightly wider than the 35mm Biogon ZM (they weigh essentially the same) and is utterly dwarfed by all the SLR lenses that I have seen. The combination with the M9 is harmonious and comfortable – I suspect this is the most pleasant 50mm lens/camera combination to use and behold.

The aperture ring is one of the high points of the physical implementation of this lens.  The movement is smooth, the detents click vigorously, and the ring has no play when settled to a stop. There is no way to predict how these properties will change over time, but between like-new lenses the feeling of the Zeiss’ aperture ring is superior to Leica’s.

Manual focus is comparatively easier with the Sonnar on a rangefinder camera than the 50mm Planar ZF on a reflex camera, but with one big and rather terrible caveat : focus shifts substantially at wider apertures on the Sonnar. This is due to high amounts of uncorrected spherical aberration in the drawing of the lens. The effect is pleasant for some uses, a nuisance for others, and can sometimes be avoided by deliberately focusing behind the subject.

The Sonnar ZM does not implement floating elements, and its closest focus distance is 0.9 meters. This is not a severe limitation for this focal length, but I do wish that it allowed focus down to 0.7 meters like its sister lens, the 50mm Planar ZM.


Whereas the 85mm Planar ZF manages to combine a soft look wide-open with authoritative drawing at all other apertures, the 50m Sonnar ZM struggles to find its foothold until depth of field embraces whole subjects. Bokeh and flare resistance are on a high level however, which go a long way to redeem this lens.

The Sonnar’s drawing at full aperture is difficult to characterize because it is so unevenly delivered in actual use. Occasionally you get both great detail and a smoothness that is ideal for portraits, but most of the time the best you get is mild blur.

This is because the focus shift effect places the camera’s best-focused plane right at the edge of depth-of-field (towards the back end) when the lens is used wide open. Hence the extremely narrow depth-of-field a 50mm lens would normally offer at f/1.5 becomes halved or quartered for one direction of focus error.

At smaller apertures, starting around f/5.6, the Sonnar draws fine detail with excellent contrast in the plane of focus. There is high resolution covering most of the frame that is delivered consistently. The far corners of the image field never capture meaningful detail however, even up to the diffraction limit.

Bokeh is excellent in all images made by the Sonnar. I could not observe any distracting artifacts in the defocus regions of the images shot with the lens. This lens is also very resistant to secondary reflection flare, as noted by Carl Zeiss in their promotional material, but it does suffer a large drop in contrast due to veiling glare under some conditions.


The 50mm Sonnar ZM is a beautiful lens that I simply cannot recommend. It is a very competent lens at smaller apertures but that is not ground for this lens to stand on, since I have little doubt the 50mm Planar ZM can do better. The Planar is also celebrated for its Bokeh, taking away the edge of the Sonnar’s foremost quality.

I have to wonder what this lens would be like if it incorporated an aspherical element in its design. Leica has demonstrated with the 90mm APO Summicron ASPH that Sonnar-type designs with aspherical elements are not only possible but can deliver the very highest levels of image quality. I am sure that Cosina is up to the challenge of manufacturing an aspherical Sonnar lens for Carl Zeiss.

Would I recommend this lens to other photographers? No. If Carl Zeiss ever announces a 50mm Sonnar ASPH then I would stand in line to get one.


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Comments (21) Trackbacks (2)
  1. Today you made my day!

    I generally like your reviews and how you write down your conclusions. And my favourite “to have” lens is this Sonnar. It is because of its rendering and bokeh that is promised to be very special. If I look at Flickr to pictures made by this lens I see many pictures with this special rendering and “look” that I like very much.

    Your review come to a different conclusion then I myself so far but the difference is that you actually used the lens. And I did not. For me there is no point in buying the Planar as I already have the excellent Konica Hexanon 50/2.0. I wanted to go for the special look. Even if the lens would be technically (read: in resolving power etc.) inferior to the Hexanon (which it is).

    Your review is very helpful in that it makes me doubt again if I should buy this (rather expensive) lens. I really think now I should hire one before I do.

    On the focus shift:
    From fora I understand that this lens is calibrated to have exact good focus @1.5 where the focus would shift backwards at smaller apertures having the sharp plane of focus almost completely backwards (!) from the focus point. You describe it differently; am I mistaken somewhere?

    Thank you Oliver for this review. Please continue to make these very useful reviews in your own way.

    • You’re welcome. :^)

      The Sonnar comes out of the factory calibrated for accurate focus at f/2.8. You can send it back to Zeiss and they will calibrate it for focus at f/1.5 free of charge. I believe that PopFlash occasionally sells brand new lenses pre-calibrated at f/1.5.


    • Also, if you want to hear about an awesome M lens, look out for my 2/35mm Biogon ZM review. I’m not in a hurry to publish the write-up, I think I’ll take my time with this one, but what is already obvious to me is that it’s a benchmark for a lens.

  2. Olivier, I just found out about your site via 1001noisycameras who linked to this review. Nice to have found another fellow rangefinder user – your site has been bookmarked! Regards, Felix

  3. Hi Oliver

    Just found your site. I have been shooting with the 50 sonnar on my Ikon for a while now and would add the following user observations:

    – The impact of focus shift depends on where your lens is optimised. MIne is at f1.5 and so the focus plane moves backa s you stop down. In practice, I tend to focus to the front of my subject if I’m using f2 to f4 and am within around 2m. Otherwise the focus shift ‘problem’ goes away really. When you get it right it draws beautifully.

    – I also wonder if the lens is easier to work with on film than digital. Digital is very revealing of focus imprecision (compared to most, but not all, films) and so managing the focus shift is likely to be that much harder.

    – The corners are never really very sharp. Whether this matters depends on your subject and aims. I use mine for available light pictures of people, so the frame edges are not really that important usually.

    Here’s an example from earlier this year – film is Ilford HP5.

    It’s one of my favourite lenses, but you need to be happy with what it can’t do and know where the focus is optimised.



    • Thanks for adding to this Mike. Your contribution is very useful for me to determine if this lens is worth the €900,= that it will cost me in The Netherlands.

      And, after these reviews, I think it is!

      Gr8 stuff!

      Kind regards

  4. Great review! Though you don’t recommend it, I love the character of the bokeh in your example shots so I may pick it up anyways for portraits.

    If I had a request, it would be that you would provide approximate aperture/iso/shutter speed info for your example photos.

    I’ll look forward to future reviews!


  5. Thank you for the review.
    You dont seem to be very happy with the performance but the images you took with it looks great, i like the rendering 🙂

    • It’s very unreliable, that’s all. The lens is great to shoot and it can produce really great images, but it’s left to chance whether your images are in focus or not. Because the M9 shows such crappy review images on the LCD you can’t really catch this in field either, you’re left feeling sad when you unload the card into your PC.

      Could I learn to live with that? Sure. But the 2/50mm Planar doesn’t have this issue, is sharper at all shared apertures, and costs less.

      I am eager to see the next wave of 50mm lenses from Zeiss/Voigtlander. I think the Summilux ASPH needs some friends to join it at the peak of the state of the art. I’m also curious to see if the rumored Summicron ASPH will pan out.

  6. ASPH elements can significantly affect out of focus blur, and, frankly, adding an asph to this lens may defeat the purpose.

  7. I am not familiar with focus shift. Can you please explain exactly what it is?
    Below is a scenario that you can use a a springboard for explanation:

    1. I mount this Sonnar on a digital camera.
    2. I select any aperture for the shot.
    3. I zoom into the subject using the digital magnification feature on the camera.
    4. I set focus precisely based on what I see in the 14x magnified EVF.
    5. I do not change the chosen aperture.
    6. I then shoot the shot.

    Why would it not be in focus?

    I have a Pentax SMC-A 1.4 lens.
    I use it for portrait on my Pentax K1000SE film camera and shoot it at F2 and F2.8.
    When I nail focus on a person’s face/eyes through the viewer and get the pictures back almost always the shots are out of focus! It has been driving me crazy. I have been thinking I am going blind.
    However if I mount the same lens on my Olympus E-PL2 digital camera and focus it at any aperture the shot is always in focus. (The EVF is very clear and focus is easy to see even when not zoomed in.)
    Does this lens have focus shift on the K1000 but not the E-PL2?
    Is focus shift a function of an optical viewer on a camera being optimized for a specific aperture and the lens being optimized for a different aperture?

    • Hi Steven,

      The 6-step scenario you describe will not produce any focus shift for you. The secret is in step #5: you will get focus shift only when the focusing and shooting apertures are different.

      When using a camera through a live-view mode (LCD or EVF) this will only happen when you change the aperture manually, so it tends to not be an issue. As long as step #5 is as you said, focus shift is not an issue.

      However when using a camera *without* the live-view mode, the camera can often work *against* you:

      Case A : any SLR (digital or film) focused using the optical viewfinder. These cameras always focus with the lens wide-open, and the aperture only steps down to the desired setting when you fire the shutter. This happens ridiculously fast, you may not see it happening. So your Pentax SLR always focuses at f/2 and shoots at whatever aperture you asked it to shoot at. That can result in focus shift, usually always the worst-case for each given lens.

      Case B : a rangefinder as in the case of the lens in this Leica M lens review. This camera focuses using a mechanical index on the back of the lens, calibrated to a specific aperture for a specific lens. Whatever this aperture is (not always wide open and rarely documented) is the aperture that the camera focuses for. You can get focus shift if you shoot at any other aperture, and usually this is chosen to hit an average offset so it’s always wrong but not always wrong by the maximum distance.

      Hope this helps,


      • One thing I forgot… you can use “depth of field preview” on your SLR to step the lens down and also observe the focus shift. If you focus the lens while holding the DOF preview button down you should be able to focus the lens accurately.

        If that fails, then your optical viewfinder may no longer be calibrated properly and would require fixing.


  8. Now things are starting to make sense. I thought I was going blind.

    Here is my issue:

    I am using a Pentax SMC-A 1.4 on my Pentax K1000 SLR.
    I have no depth of field preview feature on the K1000.
    I set the aperture at F2.8 for my portrait work or sometimes F2.
    I focus precisely on the model’s face and take the shot.
    Later I learn the shot was out of focus.

    This also happens with my Voigtlander 40mm F2.
    I shoot this lens wide open at F2 and yet the shots are out of focus.

    Yet if I use either of these lenses at F4 and above they are always spot on razor sharp.

    Is it possible that my optical viewer is not calibrated for F2.8 and below and is showing me a sharp image at those apertures when they are actually out of focus?

    Also I have heard that each SLR viewer is optimized for a certain max aperture and will not show you a brighter image even if you use a brighter lens. In other words through the viewer a F2.8 lens will look the same brightness as a F1.4 lens.

    My friend has a digital Pentax Kx SLR and when I use these lenses wide open on it (it has an optical viewer) they are out of focus as well in the same way.

    So how do I focus?!

    • For both of these cameras the viewfinder will always show you the image at the maximum aperture for the lens mounted. There are no viewfinders that are calibrated for smaller apertures than that. If you can’t focus at full aperture (and you can’t determine that without taking a lot of shots, otherwise maybe you’re biasing the result with your own errors) then the camera is not calibrated correctly. It’s sad & simple.

      There are 3 things that need to be mounted at the same distance from the lens mount: the film/sensor plane, the viewfinder ground glass, and the auto-focus sensor. If the distances differ then you will get errors. Obviously if only the viewfinder is at the wrong distance, then the auto-focus sensor will be OK, and conversely if only the auto-focus sensor is off then the viewfinder will be OK.

      It would be very unlikely that across two cameras, all four distances that could be wrong would be wrong. So you can go test viewfinder VS auto-focus sensor, across both the film and digital SLRs. Obviously the digital SLR is faster/cheaper to check…


  9. I think i may disagree with you. the pictures you posted produced with this lens are beautiful !


    • Thanks for the compliment on the pictures. What’s wrong with this lens isn’t that it can’t take nice pictures, it’s that it’s fundamentally unreliable in its output. Like rolling dice every time. In comparison the f/2 Planar draws even better and is very reliable…

  10. The Planar doesn’t draw or render nicer, it is just more technically perfect. I have a Leica Summicron that is also far more technically perfect than the Sonnar, but which lacks the Sonnar’s particular magic.

    Simply, this is a lens you buy BECAUSE of its flaws, bit in spite of them.

    I actually have three Sonnars, the modern one you reviewed (optimized for f/1.5), a 1937 uncoated Zeiss Jena Sonnar and a coated 1963 Russian Jupiter 3 Sonnar knock-off. All three have the magic and are my favorite lenses for my M Monochrom.

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