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| Re: Zeiss Lens Photos and Discussion |
Lovely pictures guys.
Since this is a zeiss lens photos and discussion thread, I think this post is appropriate (I don't want to just open a new thread for this). I hope you guys find this useful.
So finally, after a torturous wait of 10 weeks, my converted Contax lenses and the A99 are finally back from S.K. Grimes. The first time they went back, the two lenses were not calibrated correctly for infinity focus (the 85 was a hair off while the 55 was way off). However, the quality of the mounts are the best I have seen so far. Unlike the typical Leitax mount (excellent quality), there is no torsional flex with this mount, understandably so since these are custom made to fit. Adam Dau is very nice to talk to and he did agree to ship my stuff back via Express after the calibration. Top notch service.
Moving on to the next part, I just shot an aperture series at infinity with the Contax 55/1.2 for a performance evaluation on a FF. Initially, it was for my personal archives so I know the strengths at weaknesses of my lenses at various distances; however, I decided to share the result here. I'm thinking doing a bunch of these in the future with whatever Zeiss lens I have in hand. However, if everyone thinks this is useless, I will withdraw the post.
Testing conditions: I used a Feisol-equivalent of a Gitzo series 2 and the tripod was dampened further with my camera bag; there was slight breeze. A remote shutter release was used for all shots.
The test scene and crops:
I believe that the slanted shot is the best way to examine a corner-to-corner performance, a possibility of lens-camera skew/misalignment, and any de-centering and field curvature issue. This was how I discovered the severe astigmatism problem of the ZA 24/2.
3 crops are presented here to show the center, edge, and corner performance.
Processing: These are presented as-is with Lightroom default settings, except for my attempt to match the exposure of the 1st two apertures with the rest by using the exposure slider.
The three MTFs were measured at infinity distance. The last MTF was measured by Marco Cavina. I presented these here so you guys can see the correlation.
Note: That is supposed to be 1.2 not 1.4.
I tried to match the exposure of 1.2 and 1.4 with other apertures. However, I only presented the matched results in the center; the edge and border are not matched. On the A99 sensor, there is not much different from 4 to 8. f/11 shows a visible drop in contrast, though slightly. On my NEX-7, f/4 would yield the sharpest center while f/8 shows sign of diffraction.
F/8 would yield the sharpest corner-to-corner result. The drop-off in the corners at f/5.6 is not as steep as suggested in the MTF measurement; my ZF 28/2 has the same drop-off and I can clearly see the mushiness. I would say the corners of the 55 are very sharp at f/8.
I see some forward (toward the near field) field curvature at f/4 in mid frame, but by f/5.6, it disappears (or at least not noticeable to me). There is no severe de-centering issue that I can see. CA is not as well-controlled as the latest Zeiss (the 25/2, 15/2.8, or 135/2) but pretty much on bar with rest.
I hope these are helpful for some (especially those with the Canon 50/1.2 L or the 55/1.2 Asph) to gauge the performance of their lenses. I also have the 85/1.2 results, but I'll wait to see any feedback from you guys to see if I need to improve the test. Hopefully, by this weekend, I have enough time to shoot some "real" shots.