Yesterday I contemplated the MTF-diagrams of the Batis 2/40 CF (see here). While they promised excellent optical performance, it's a bit theoretical and difficult approach to determine lens behavior. After all, camera lenses are meant for photography, so using them in real world often provides much easier way to evaluate the optical performance. Having thought about this for a while I decided to use same method that Phillip Reeve, Bastian Kratzke, Jannik Peters and David Braddon-Mitchell have been utilizing in their popular and great photography blog at phillipreeve.net. If you haven't yet hear of them, you should definitely check the site as it has tons of great reviews for many E-mount lenses.
Ok, so below you can see raw-image of the full scene and 100% crops from center, midfield and corner for every aperture stop from f/2 - f/11. The raw-image was imported to Lightroom and I've done nothing to it; ie. no software corrections of any kind nor other adjustments. However, there is a Lightroom default sharpening (amount 25, radius 1.0, detail 25, masking 0) which I decided to leave there so that the results are more comparable with similar pictures from phillipreeve.net. One thing you should note is that the test shots were done with a low-end first generation Sony A7. While the Sony A7 still offers a very good image quality in general, it still doesn't present the best option for this kind of test: it has only 24 megapixels and anti-alias filter which softens the smallest details a bit. Newer Sony bodies like A7RII and A7RIII would offer higher resolution without anti-alias filter and even the 24 megapixel A7III should also perform better because it has a weaker anti-aliasing filter than the plain A7 which I am using. In other words, using newer Sony body one should expect even better results than what is shown here.
As you can see the overall contrast is already very high right out of the box just like the MTF-diagrams suggested. Looking at the crops the center performance wide open at f/2 looks superb and if you compare it to stopped down performance in the same center region, you can see a very slight improvement at f/2.8, but after that it remains the same throughout the aperture range. This is superb center performance as you lose practically nothing even wide open at f/2. The midfield also looks very, very good wide open and finally only at the very edge of the frame you will start to see some decrease in definition (plus some vignetting). I would say the wide open performance is distinctively good because at center is almost the same as when stopped down to medium apertures f/4 - f/5.6. The extreme corners of course suffer, but one rarely needs the corner performance at f/2 because you probably shoot wide open for bokeh.
MTF-diagrams suggested that there would be a little midfield dip wide open which would then transform into slight astigmatism when stopped down to f/4. Well, you can see a little decrease of definition in the midfield at f/2 (compared to the center), but I really don't see astigmatism in the stopped down performance. If it's there it will be reduced to negligible with any kind of sharpening or size reduction. If anything, the stopped down performance (f/4 - f/8) looks kind of identical.
All in all, the Batis 2/40 CF shows very consistent optical performance where the high contrast and resolution are already achieved wide open at f/2 and it doesn't increase much after that even when stopping down couple of stops. This means that you can pretty much shoot at any aperture and be sure to have excellent results. One should also notice the complete lack of chromatic aberrations (no software corrections were used here). The Batis 2/40 CF is no apochromatic lens (there are some longitudal chromatic aberrations in defocused areas), but at the focal plane, which is shown here, it is pretty much free from the chromatic aberrations. I should add that the performance is also very consistent throughout the frame, meaning that there is no field curvature and the general sharpness and definition stays very similar in different regions of the frame. Only the very extremes of the frame suffer a bit at the widest aperture, but even then the degradation is masked by the fact that image is probably reduced and sharpened for final use in print/screens. The general the optical performance represents modern expectations, but even within these expectations the Batis 2/40 CF shows outstanding performance. In short, it's a winner!
Ps. As I’m sure some one will ask that ‘did you compare the Batis 2/40 CF to the Loxia 2/35?’ Well, of course I did, and I even made you a little table of it, here you go:
I didn’t put every aperture there, but instead I wanted show how good the Batis 2/40 CF really is. So, here you see 100% crops from the Batis 2/40 at f/2.8 compared to Loxia 2/35 at f/5.6. That’s a two stop difference and the Batis 2/40 is better, especially at the corners. Quite remarkable performance, I would say.