The Carl Zeiss Jena Biotar 1:2/58mm - Michael Kukacka
Vintage Optics Recycled
A short report of the Biotar on a Canon EOS M6.
The Carl Zeiss Jena Biotar (1) was built for 25 years, essentially optically unchanged, based on a design from 1938.
In terms of the basic principle, it follows the double Gauss design. The two inner pairs of the optics are cemented and expanded by an outer converging lens at the front and rear. The Biotar was manufactured a million times in the Soviet Union under the name "Helios 44 2/58mm". The Biotar, built in 1949, has 2 setting rings. The closest focusing distance is 90cm. Filters with a diameter of 40.5mm can be used. The smallest f-stop (largest f-number) is f/22.
For comparison the Biotar from 1955. It was mechanically more complex and has 3 adjustment rings. The focusing ring, a ring for preselecting the smallest aperture (largest f-number) and the ring for setting the aperture. Since the lens does not have a spring diaphragm, the diaphragm can be preselected with the second ring. To focus, the lens is then completely faded in to obtain a bright viewfinder image (aperture f/2). Before the shutter is released, the aperture ring can be dimmed down to the preselected aperture without having to take the camera away from the eye. The closest focusing distance is 50cm and the filter diameter is 49mm. The smallest aperture of the lens is f/16.
The Biotar was tested on a Canon EOS M6. The M6 is a mirrorless system camera with an APS-C chip (crop-factor 1.6) and a sensor resolution of 24.2 Megapixels. The focusing is done very easily and safely, even with manual focus, using a magnifying glass on the monitor with either 5 or 10 times magnification or the also very practical focus peaking (2). The original Canon M42 to EOS M adapter was used to connect the lens to the M6. However, it was not possible to focus to infinity, which is why my trustfull technician had to make a slight modification to the adapter. The reason lies in the different lens flange distances (3). There is a very detailed article on this under (3).
But now to the images:
Before I go into more detail on the bokeh of the Biotar from 1955, two comparison images with the Biotar from 1949 and the one from 1955.
Biotar 2/58mm, f/2 , 1/100sec. with flash, year 1949, focusing distance ca. 90cm
Biotar 2/58mm, f/2 , 1/100sec. with flash, year 1955, focusing distance ca. 90cm
As can be easily seen, there is no discernible difference between the images taken by the two lenses. For the depiction of the Biotar's bokeh from 1955, I chose a backlit situation of a weigelia blossom in the morning dew. Focused manually at 50cm (the closest focusing distance of the lens), ISO 100, Aperture f/2.8. The shutter speed was controlled by the aperture priority of the EOS M6. A very nice bokeh in the out of focus area. The aperture with 10 blades, which gives the lens an almost circular bokeh even when the lens is stopped down, is clearly visible. When the aperture is fully open (f/2), the points of light shown in the out of focus areas are shown as circular reflections.
If you stop down further, the reflections become more clearly delineated. The aperture characteristics are also more evident.
Biotar 2/58mm, f/2.8
Biotar 2/58mm, f/4
Below two sample images with the two Biotar lenses set to infinity.
Biotar 2/58mm, f/4 , 1/400sec., year 1955, focusing distance set at infinity
Biotar 2/58mm, f/4 , 1/400sec., year 1949, focusing distance set at infinity
The images were recorded in RAW format and developed with Adobe Lightroom (R). The exposure and contrast were gently adjusted. The following links provide some additional information for self-study.
(1) https://de.wikipedia.org/wiki/Biotar
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