This is a continuation of a test of the following lenses on the Sony a7RII:
- Zeiss 85mm f/1.8 Batis.
- Zeiss 85mm f/1.4 Otus.
- Leica 90mm f/2 Apo Summicron-M ASPH.
- AF-S Nikkor 85mm f/1.4 G.
- Sony 90mm f/2.8 FE Macro.
The test starts here.
I reprocessed the 3.5-meter DCRAW-developed test shots from the lateral chromatic aberration (LaCA) studies to look at where the modulation transfer function (MTF) reached half of its zero-frequency value. This is called MTF50. These images were created by placing the target in the corner of the image. The target has four edges. Two are oriented in the direction from the corner of the image to the center. These can be used to measure what lens designers call the sagittal MTF50. The two edges perpendicular to those allow measurement of the tangential (or meridional) MTF50.
I’m reporting the MTF50 numbers in cycles per picture height. The height of the a7RII image is 5320 pixels. Divide the numbers on the vertical axis by that if you are more comfortable in cycles per pixel. If you like lines per picture height, double all the numbers on the y axis.
Note that DCRAW doesn’t do any sharpening, so these numbers will look low compared to those for images that are developed in Lightroom using the default settings, which include deconvolution sharpening. Note also that I used a high-contrast target, which I normally don’t use for MTF testing, which will make the numbers somewhat higher than you’d get with a low-contrast target. I used the high-contrast target so I could get the LaCA results from the same set of exposures.
Here are the sagittal curves:
As we saw in the LaCA studies, the Summicron struggles in the corners on the test bench. The fact that the Summicron images look so good raise the possibility that there are things we should be testing for that we don’t consider.
It’s no surprise that the Otus does so well here, but it is a surprise to me that the Nikon matches it step for step. At f/8 and beyond, the Sony 90 macro is also right in there. The Batis starts out mid-pack at wide apertures, and ends up in last by a bit at the narrow ones.
The tangential curves are different:
All the lenses are more-or-less clustered together except for the Sony macro and the Otus. The Otus is a clear winner.
Now let’s look on-axis. Before you jump to the curves please read the rest of this paragraph. Measuring on-axis performance of top-notch lenses at their optimum f-stops is hugely dependent on accurate focusing. Even with the Sony’s excellent focus aids, I have been unable to consistently duplicate on-axis MTF50 with the Otus 55 and the Otus 85. Therefore, the numbers at wide apertures should be taken with a reasonably large quantity of salt. I focused wide open in all cases, so focus shift could play a role in the results as well, although in my testing of the Otus, I found the most accurate way to focus at the best apertures was to focus wide open.
There’s a lot to see here. The first thing that jumped out at me was the Batis f/2 number, which is slightly better (a tie, really) than the Otus. This is not a glitch. All four edges gave similar results, and all four edges of the not-shown f/1.8 shot we only slightly worse. I think the reason has to be better focus with the Batis. Remember what I said in the distant landscape testing about the Batis and the Sony being easy to focus precisely? When focusing on the Siemens star, the Batis was far and away the easiest and most repeatable in the focusing department. The Otus felt the best, of course, and was probably second, but small motions of the Otus long-throw focusing ring produced large variations in the moire patterns that I was using to focus. The Sony was next, by a hair, although it wasn’t anywhere near as much fun, and would be worse if you were in a big hurry. The Nikon was quite a bit worse. The Leica was really tricky to focus. Many times, I’d think I had it close to nailed, and merely taking my hand off the ring changed things. The rangefinder-oriented short focus throw is a real problem when you want focus bang-on.
The Otus is a clear winner overall, in spite of probably not being focused as well as the Batis. The Nikon acquits itself well here. The Sony macro and the Leica produce about the same so-so numbers; well, so-so in this field, anyway.
One of the questions this and the two previous CA tests leaves me with is: “Why does the Summicron look so good and measure so bad?”
Here are the results at MTF30:
No surprises, except take a look at the Otus numbers for on-axis MTF30 at f/2.8, f/4, and f/5.6! They are essentially at the monochrome Nyquist limit for the a7RII sensor, which means that with the right (or the wrong, depending on how you look at it) subject, the Otus on the a7RII is going to alias all over the place.