Biogon-T* 2.8/21mm ZM: the Zeiss hattrick!
Introduction
The Zeiss lenses in the thirties of the previous century were according to most experts ahead of the comparable Leitz lenses for the 35mm format. Mechanically however, the Leitz products were superior without any question. Around 1950 the Leitz lenses forged ahead optically and never lost its optical advantages. Zeiss reconsidered its options and with the Contarex lenses offered the finest mechanical mounts ever seen in the photographic world. The designs were calculated between 1955 and 1965 and were quite advanced. It took Leitz another ten years to get even in the SLR field.
The SLR lenses generally could be designed without paying too much attention to the size of the lens, but Leica had to design lenses for the M-rangefinder as well. Here size does matter more than in the SLR world, where cameras are generally bigger. The dilemma to adapt size to optical performance could be solved with the introduction of the aspherical surfaces. This technique was initially adopted by Kodak and quickly followed by Zeiss, who studied the economical manufacture of these type of surfaces. When Mr Koelsch moved from Zeiss to Leica, he brought with him extensive knowledge of the design and manufacture of aspherics. The ceramic mould as a technique for hot-pressing the aspherical shapes was a big step forward compared to the previous hand shaping of the surfaces and the first lens to benefit from this technique was the Summilux-M 1.4/35mm ASPH.
Meanwhile Zeiss upheld the view that the employment of aspherics for photographic general-purpose lenses was not necessary to get superior optical performance. But such is the current culture in the photographic community that myths are cultivated instantly. The addition of the word ASPH or aspherical or APO to a lens automatically gives it an elevated status.
The Biogon-T* 2.8/21mm ZM
This is a nine element-seven group lens with a lens layout that derives directly from the classical Biogon lineage. It is very compact with an elongated shape that is easy to grip and focus. One can create an issue out of the shape of the focus tap (bulging as here or inward curving as with the Leica lenses). Both shapes can be handled well and it is a matter of preference which one likes. From a manufacturing view the Zeiss option is not cheaper than the Leica version, so cost cutting is not the issue here. The 1/3 click stops are of academic value and the exposure meter in the ZI camera does not respond to the fine-tuning of the aperture values. If you use an external exposure meter, you can of course set the aperture as accurately as you wish.
Wide open the Biogon delivers first class performance. The contrast is high and extends over most of the negative frame. Only the extreme corners suffer a drop in contrast, but that is common with these lenses. The area of high contrast coverage is wider than any lens I have tested, including the Elmarit-M 2.8.21 ASPH.
There is a visible vignetting in the outer zones, but again this is to be expected with the type of lenses we are dealing with here. In practical photography the light fall-off is hardly visible, especially when one over exposes a bit. Natural vignetting cannot be designed out of the system and one has to accept some light fall-off at smaller apertures. Secondary reflections and veiling glare are non-existent. Distortion is quite moderate with below 2% and the distortion shape is curving to zero at the extreme edges, which is pleasing to the eye.
Stopping down to f/4 improves contrast a bit and now extremely fine detail is crisply rendered over most of the image area.
From here the lens is practically at its optimum and can be used with confidence till f/8 where a small drop in contrast signifies the occurrence of diffraction effects. Close-up performance is quite goo, especially since contrast does not drop at the lower frequencies.
Conclusion
This Biogon lens is second to none in the current rangefinder field and is a most interesting design in the 21mm class. It delivers at least the same overall performance as the Leica Elmarit-M 21mm, but without the employment of aspherical surfaces and at a lower price. The sturdiness of the mount may be not as good as that of the Leica, but the mechanical accuracy is not affected and I did not detect any decentring. With the Leica Md on the not-too-distant horizon (we may assume) it is a tempting alternative to the Elmarit 21mm, especially because of its even coverage over most of the image field at the wider apertures.
The performance of this lens warrants a somewhat wider perspective on lens design. Zeiss demonstrates that it is possible to improve on first-class lenses while using conventional designs and without elevating the cost to astronomical heights. Leica has lived for a long period in an ivory tower, supported by a loyal following of collectors who were more interested in the safety of their investments than in the quality of the images that could be produced with Leica equipment. The digital tsunami has at last reached the parapet of the Leica fortress and it is evident that Leica must become a more market-oriented company. Leica claims to offer an unique mixture of traditional values and modern technology for its products. You do not get market share in the current photographic world without a sensible price-performance relation and here Zeiss is beginning to lead the way, at least in matters optical.
