Sony Carl Zeiss Planar T* 85 mm f/1.4
10. Autofocus
First of all, when buying a „glass” for such an amount of money, we really have high expectations. For this sum of money, you can get the Canon's Ls with excellently working USM drives or the best Nikkors with SWM drives. At Zeiss on the spot can be seen the lack of experience in working on autofocus. We obtain a poor mechanism, which is toiling while moving the enormous elements of the lens. It also give out a noisy buzzing. Moreover, the inertia of the solid glass blocks is so big that while they stop after focusing or when reaching the edge of the range we can feel a shake. It is even transferred to the body. Simply, when the elements finally stop, you can hear one loud „bang”!
All this would be forgiveable if the focusing system would be working properly. It is a fundamental issue with such a big maximum aperture and such a focal length, where the depth of field is exceptionally small. Unfortunately, the autofocus misses the target continuously. During the whole test session in the lab, the number of the mistakes reached 37%. It is most painful in the vicinity of maximum aperture, where the autofocus is focusing accurately on average in one out of five exposures....Not to be proof less, an example of the series of six consecutive photos of test chart taken with the f/2.0 stop value.
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Values of the MTF50 function measured at JPGs for this series of photos are as follows: 1840, 680, 470, 420, 530 i 1450 LW/PH. It is worth adding here that while manual focusing for the f/2.0 it was manageable to achieve MTF50 reaching 2050LW/PH. Further comment is probably redundant. Although it is worth emphasising here that such bad behaviour does not result from the faulty body, since attached to it Sony 2.8/50 Macro was working faultlessly and was mistaken very rarely.
As a consolation, it can be added that the autofocus in its lack of accuracy does not prefer any of the sides, therefore, the front focus and back focus appears equally often.
