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Articles

2009-12-22
 

A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4

4. Image resolution

As we deal here with full frame lenses, we decided to arrange our duel on a full frame body. Our instruments were put on a Sony A850 with 24 million pixels matrix resolution – it’s a sensor known from the A900 camera and even programmed in the same way so it gives the same results in the real resolution sense. The measurements, based on the RAW files, were taken from averaged vertical and horizontal values of the MTF50 function, and we used test charts of two different sizes to see how the lens coped with the work from different distances. Measurement errors in both cases were in the 0.3 to 1.7 lpmm range. The picture below presents both lenses’ resolution graph for the frame center.

A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution

First thing which sticks out is a fact we noticed in our Zeiss 1.4/85 test, performed many years ago on an A100 camera, still with a small sensor. Both lenses don’t break any resolution records and by the sharpest f/4.0 – 5.6 apertures they reach the results at the level of 40 lpmm. It is worth mentioning here that even the sharpest lenses on the A850/A900 have results reaching 42-43 lpmm. This effect was previously explained by the aspiration to obtain a splendid picture quality not only in the center but also at the edge of the frame and this is also confirmed in the full frame test as we are bound to see in a moment.

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Let’s get to the very point of this duel so a comparison between the results of the two tested lenses. From f/4.0 upwards the Minolta and the Sony fare similarly, having in fact identical results. In the f/1.4-2.8 range the newer Sony performs better, reaching a level higher by 2-4 lpmm. The difference is small but perceivable.

How does the situation presents itself for the frame edge? Let’s have a look at the following graph.

A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution

Here the Sony’s advantage is a bit more noticeable. Perhaps not in the sense of MTF50 function values difference, because the distance between the two devices is still at the level of 2-4 lpmm, but in the sense of performance by different apertures. Previously the Sony was better in the range of 2 EV from the maximum aperture, now it is better in the range of 5 EV.

It is worth stressing again what we wrote already twice: the frame edge was improved at the expense of the center records. A comparison of the both lenses to a more expensive and faster Canon 85L/f/1.2 can be the proof. In the range from the maximum aperture to f/4.0 it fares worse than the Sony and the Minolta. Then the MTF50 values are more or less the same. If we take into account the fact, though, that the EOS 1Ds MkIII sensor allows to reach results higher by just several tiny lpmm than the A850/A900 sensors, the results of the Sony and the Minolta at the frame edge should be considered better than those of the Canon 85L and definitely praiseworthy.

At the end we would like to present a duel of JPEG scene crops. By and large its results confirm exactly everything we wrote above. Those crops shouldn’t be taken very seriously, though, because their results are not as well controlled as it is the case with the RAW files analysis.

Frame center – f/1.4
Minolta AF 85 mm f/1.4 G D
Sony Zeiss Planar T* 85 mm f/1.4
A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution
Frame center – f/5.6
Minolta AF 85 mm f/1.4 G D
Sony Zeiss Planar T* 85 mm f/1.4
A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution

Frame edge – f/1.4
Minolta AF 85 mm f/1.4 G D
Sony Zeiss Planar T* 85 mm f/1.4
A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution
Frame edge – f/5.6
Minolta AF 85 mm f/1.4 G D
Sony Zeiss Planar T* 85 mm f/1.4
A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution A history of Sony Alpha - Minolta AF 85 mm f/1.4 G D versus Sony Zeiss Planar T* 85 mm f/1.4 - Image resolution

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