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Through its special optical design, the new family of high-end SLR lenses exploits the full potential of high-definition sensors.

At the end of 2013, the Distagon T* 1.4/55, the first member of the new high-end SLR family of lenses will come on the market. The most important goal in developing this lens was to achieve a “no-compromises image quality”. Which of the optical design characteristics achieve this? Dr. Aurelian Dodoc, ZEISS Principal Scientist, explains.

ZEISS has announced a lens with “no-compromises image quality”. What exactly does that mean?

In the history of camera lenses, you’ll find many lenses whose quality could be described as good. But our goal this time was to create perfect lenses for those who understand and value the difference between good and perfect. Compared to our previous SLR lenses, which already had a very impressive quality, we have now raised the bar much higher. The result is a family of high-quality lenses with perfect imaging qualities.

The new lens offers optimal imaging performance, even with an open aperture. What did you need to do in the optical design to achieve that?

We decided to use the complex Distagon optical design, which until now has only been found in wide-angle lenses. This is the only way to get the desired sharpness and rendering of contrasts all the way into the corners of the image.

Why is the Distagon better suited for sharpness and contrasts than another design concept?

Traditional lenses in the focal-length range of around 50 mm are of the Planar type. With this lens type, with its practically symmetric, very compact construction, there is a close correlation between the correction in the center of the image and at the edge of the image: when there is good correction at the center of the image center, the edges are not corrected, and vice versa. Expressed more precisely in technical terms, the correction of the spherical aberration does not correct the image field curvature at the same time. Our most important goal in developing this lens was consistent imaging performance across the entire image field, including at the edges. Which is why we replaced the Planar’s relatively simple structure with the much more complex structure of the Distagon.

The Distagon allows spherical aberration and image field curvature to be corrected at the same time. Can you elaborate on that in more detail? As an optical designer, how did you accomplish this and how does it manifest itself in the image quality?

The structure of the Distagon allows for a good split between the negative and positive optical refraction power within the lens. As a result, we were able to achieve an excellent correction of the image field curvature. The image field curvature is the most important image defect in photography, and correcting that is a prerequisite for getting a perfect image. With an adjusted framework of lens elements and various aspherical surfaces, the other aberrations can also be corrected to the minutest levels. In particular, we have perfectly corrected the spherical aberration and the coma, both of which can have a devastating effect on the quality of an image. Distortion is also imperceptible.

In addition to bringing consistent sharpness into the edges of the image, it was also important to us that the edges of the object appear as natural as possible. This required extreme color-error correction and the prevention of color fringing, which can be caused by chromatic aberration. The Planar system would not be able to handle this: since the lens elements in the Planar that take on the role of this correction are also responsible for the correction of the spherical aberration and for the image field curvature, it is very difficult to correct color defects when using a Planar. The only way to solve this challenge was to use the Distagon. With ‘normal’ optics, a good chromatic correction in a high-quality optical system is simply not possible. To correct color defects, we therefore use special lenses that have anomalous partial dispersion. This is how we corrected not only the primary and secondary color defects, but also the chromatic variations of all aberrations, which also strongly reduce color fringing.

Left column: Distagon design; right column: Planar design

Left column: Distagon design; right column: Planar design

 

Another important feature of high-quality lenses is a lack of stray light. How did you avoid stray light outside the angular field?

Stray light, or false light, is caused by reflections of all kinds, but also by the reflections between the optical surfaces. For this we used newly-developed multiple layers. ZEISS is also a leader in this field of technology.

In addition to the Distagon and multilayer design, the lens’s inner focusing is another unusual technical feature when it comes to this focal length. Why did you decide on this type of construction?

With inner focusing, focusing does not happen by shifting the entire lens, but rather through one or more lens elements within the lens. We have built them so as to maintain the performance of the lens for even the smallest distances of 350mm to the object. The lens elements after lens 4 move in the direction of the object. As a result, the actual length of the lens does not change during focusing.

Many photographers are used to taking pictures with autofocus these days. Why does the new lens only have manual focusing?

The lens is probably the most powerful standard focal length in existence and we wanted to enable photographers to take full advantage of its performance. We want the user to have the freedom to employ the focusing position as an artistic means, since we are dealing here with one of the most important tools that a photographer has at his disposal. Moreover, the lens offers very fine haptics and an extremely precise focusing mechanism. The lenses of this new family are therefore suited above all to application areas in which conscious, manual photography shows its true strengths, such as portraiture, fashion or landscape photography.

What do photographers like about a lens in this performance class? And what do you think photographers will do with this lens?

With this new family of lenses we want to offer photographers an artistic tool with which they can create perfect pictures. The optics should not pose any limits on the quality of the image. A photographer’s creativity should be the defining factor. We want to challenge photographers to create the perfect picture by providing the perfect optics.

 

For a more detailed insight into the physical and technical characteristics of lenses we recommend reading some articles from our archive:

How to read MTF curves?
How to read MTF curves? Part II
Distortion
Depth of Field and Bokeh

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22 Comments

  1. Zeiss makes great lenses and the statements in this article regarding “best” and “perfect” sure sound like there is a lot of confidence in the performance of this lens. Having said that, I am sure Zeiss has tested and compared to others. How much better would you say this lens is than the other high end lens made by another German company which I won’t mention by name :) Would it be safe to say it will dethrone any other 50mm lens out there that has been praised by many?

    Reply
  2. Stephen

    Will the lens go on the market in the December 2013? I assume by the end of 2013 that’s what you mean.

    Reply
  3. David

    I have an impression the lens has been redesigned, it now features with more compact dimensions?

    The filter thread at least is now 77 mm instead of 82 mm of the previous scheme presented on Photokina 2012.

    Reply
    1. Nice catch. I also wonder when other focal lengths will be at least known. Time ago I heard of a 35 and an 85 mm but so far no confirmation on this. I’d be really interested in something longer than 135mm or in an APO lens of 75mm

      Reply
  4. Max

    Beautiful! I wonder how big a f2.0 to f2.5 version of this lens would be? I mean, it’s thrilling to get max IQ already from f1.4 but after some time a smaller version of this lens could be more practical and equally useful since my metadata show that 99% of my pictures are taken with apertures from f2.5 and higher.

    Reply
    1. RussellInCincinnati

      Excellent point, a “perfect”, say 55mm F/2 lens would be a fabulous addition to the line. The weight and size (and cost considering less need for exotic glasses and surfaces?) savings could be considerable. One can also imagine the flare resistance of a lens with fewer elements might even be superior.

      This is not to criticize the F/1.4 lens choice.

      Reply
    2. Brad

      The baby version of this already exists and it’s quite small. It’s called the 50mm f/2.0 Makro-Planar ;)

      Reply
  5. Rinat

    i ask you to think about making black version ZM lenses with a black front panel and not a chrome panel like it is now. It is shining — especially when a lens on a black body. When you shoot people at a street on a close distance it felt clear, especially at a compare with full black painted lenses (some konica, some voigtlander, leica). I will prefer to choose a more comfort lens even if they are less good at the optic aspect. And the main — there are many photographers like me.

    Reply
    1. RussellInCincinnati

      Alpha mount lenses are interesting in that they can be used so easily on both Sony “full frame” camera bodies, and also Sony “APS-C” or half-frame bodies with inexpensive Sony and third-party adapters and even focal length reducers.

      Fascinating to think of a Zeiss “35mm F/1.0″ lens on a Sony APS-C (“half frame”) Nex, via use of a focal length reducer. Better yet, used with a ZEISS DESIGNED ALPHA-TO-E-MOUNT FOCAL LENGTH REDUCER. The Zeiss focal length reducer would generate a lot of free publicity for Zeiss.

      Reply
    1. Yes, I would also prefer wides. I hope Zeiss is designing a better 28mm. The current 28mm/2 is good, but has too much field curvature for the kind of landscapes I want to shoot, leading to soft lower corners (even at f/11).

      Reply
  6. Seems that “Normal” lenses (focal lenght’s that translate to between 45 and 55 degrees of angle) are to normal for ‘people’ to cherish (rather own wide or tele lenses).
    Parhaps also, it is “difficult” to acheeve good composition and life (make discover “à different point of view”) with an angle of view that does not depart from ouer daily human perception of angle of sight.

    I consider the “normal lens” a very important focal-lengh for myself and I have always been scandalized of the poor quality of these lenses available, by any brands be it any any of their model.

    To older standards I only liked one micro 55 by Nikkor.
    ( dont know the Pentax 1.7 nor the Leitz’s).
    Of course, caracter of a lens’s imagery is important above all. Trouble is they are all uninteresting and with too many bad defaults, all. Now that i’m on Canon -free but hopfully usefull add here : only the (adaptable) Zeiss macro 50 is good. The macro version. I’m not into macro at all. Just happens that they are. Even and very good sharpness from center to corners, nice bokke (just dont do lenses with less then 9 rounded blades..) seems to be a reasonable minimum to expect from a 50mm..
    Then ok to pay extra for robustness, focus throw, planity, apperture, color, ‘anti-flare’, coma etc..
    It seems easy to make an overpriced lense in such an environement, and I dont doubt for a second that it will be overall better then the others.

    Reply
  7. Nedeljko

    I don`t suspect it should perform great, but it will be HUUGE, even on top FF bodies! (Price not to mention.)

    Reply

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