A lens class of its own
Even after 20 years of digital photography, the reputation of medium format cameras as being technically superior equipment for professionals persists.
“The term ‘medium format’ evolved historically,” explains Dr. Hubert Nasse, Staff Scientist with ZEISS Camera Lenses. “Its origins lie in a period when the same film emulsions were used in practically all camera formats. Cameras with a larger film surface offered better technical quality in a larger positive image. That meant lower visible grain, better sharpness of contours due to the smaller enlargement of the negative, a higher color saturation, and greater luminosity of the image when projecting slides.” The term medium format was coined in the analog era when there were different roll-film formats that were larger than the full-frame format of 24 x 36 mm, including 42 x 56 mm, 56 x 56 mm and 56 x 84 mm.
These technical advantages could only be achieved with a camera system that was larger, heavier and considerably more expensive and more difficult to master than full-frame cameras. This is still true today for digital medium-format systems. Due to the technological innovation of sensors and optics, the question arises: Does the medium format face competition from high-quality DSLR systems (full frame format 24x36mm)?
Comparison shots without background light:
Dr. Hubert Nasse is convinced that the answer is yes: “In our view the new ZEISS Otus 1.4/85 and its sister lens, the Otus 1.4/55, enable that ‘legendary’ medium-format quality when used with the right kind of full-frame cameras.” A reflex system with the Otus family of lenses is more mobile, more versatile and above all significantly cheaper than a medium-format system, and yet it delivers images “as if they were from another camera world,” says Dr. Nasse.
But what does medium-format quality really mean? Due to the larger image format, medium-format lenses have longer focal lengths than full-frame optics for the same image field. A medium-format image typically shows a larger blur in the background. And the medium format has its own special visual language: a high sharpness of contours, little noise and a stronger ability to separate the motif from its background. The latter feature in particular gives the image a higher three-dimensional effect. But can the exact same look also be achieved with a full-frame lens such as the ZEISS Otus 1.4/85 or the ZEISS Otus 1.4/55?
“The characteristics of background blur are not an absolute feature of the sensor format. The f-stop of the lens in relation to the image diagonal is key,” explains Dr. Nasse. “You can achieve the same deep imaging features with a smaller format as well. To do this, you need lenses that have equally good characteristics at large apertures as medium-format optics. In the past you had to use fast full-frame lenses with an open aperture. But then the image contrast was not as good and the chromatic aberrations were bothersome. That’s now different with the Otus family: at the maximum aperture the contrast is already very high, all the way into corners of the image, and the color correction is outstanding. Also, digital medium formats have become smaller. A normal system, for example, has a sensor area of 30×45 mm; in this case the linear sensor size is only 1.25 times larger than the full frame. Half an f-stop or a full f-stop higher aperture for a full-frame lens will result in the same background blur characteristics.”
So has the medium format had its day? According to people photographer Bernd Vogel from Cologne, who tested a prototype of the Otus 1.4/85 in his normal everyday work , this could be true. “I also work with the medium format and therefore looked at the ZEISS lens very carefully in test shots. The result – in terms of sharpness – is almost identical. This level of performance makes the Otus 1.4/85 extremely interesting for me because for around half of my typical work situations, a medium-format camera cannot be used. The sensitivity of the chip is too low, the tendency to create noise is too high, and they react to a lens’s errors much more awkwardly than full-frame chips. If you can achieve such a quality, there will be a number of professionals for whom the Otus on a full-frame camera will be a viable alternative.”