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Viewed from a lake view room at the Prince Arthur Waterfront Hotel in Thunder Bay, Ontario, Canada. The covered walkway takes you across the highway and the railroad, to the Waterfront Park and Marina. The green roof in the foreground is called the Pagoda. The hills on the horizon are called the Sleeping Giant.
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!
Ok, let's take a look at the Batis 2/40 CF again in detail. Everyone is of course interested about the optical performance so I thought I should 'address the need' and start to investigate it. The MTF-diagrams published by ZEISS is a good starting point as they provide lot's of data and are easily comparable (with other ZEISS lenses). So, here are the MTF-diagrams of the Batis 2/40 CF.
People always look first for the resolution so they are mostly interested about the 40 lp/mm line, but I think the 10 lp/mm important as well, because it describes the amount overall contrast and 'pop' the lens is able to achieve. Wide open at f/2 the Batis 2/40 CF achieves more than 90% throughout the frame with 10 lp/mm and decreases to 80% only at very end of the frame. Anything above 80 % is usually considered to be excellent, but with the over 90% the Batis 2/40 shows outstanding contrast performance. For a reference the Otus 1.4/55 achieves only about 2% or 3% more (but then again the Otus is also about outstanding optical correction).
Next, the 40 lp/mm line tells us something about the maximum resolution and definition the lens can achieve. Wide open at f/2 the resolution looks – again – outstanding at the center. There are lenses that achieve similar resolution only at stopped down to f/5.6 and achieving such as resolution already at f/2 is very good indeed. The maximum resolution drops a bit at midframe, but at 50-60% it is totally acceptable (let's remember the lens measured wide open here). In short, the wide open performance is very, very good.
When the lens is stopped down to f/4 the performance of course increases a bit. The large scale contrast (10 lp/mm) is very similar to wide open behavior which is actually a compliment to wide open performance: this lens pushes maximum contrast already at wide open. The maximum resolution (40 lp/mm) jumps up a bit as is spread out very evenly throughout the frame and the lens shows no field curvature. Tangential and sagittal lines differ a bit here, which means a slight astigmatism at the midframe, but this is really nitpicking as the lines are still very convergent as a whole (you should see some zoom lenses). In short, the MTF-diagrams shows outstanding optical performance for the Batis 2/40 CF. But to be honest, this was to be expected because it's designed by ZEISS and the competition in Sony Alpha ecosystem is very hard at the moment, so the crafty people at Oberkochen has to push the envelope even further.
One thing I should note here is that ZEISS always provides MTF-data measured with white light from real lenses. With the most other manufacturers this is not the common practice. With Sony, for example, you only see theoretical MTF-data and they don't even publish the 40 lp/mm precision (only 10 and 30 lp/mm), which of course makes the diagrams look good, but the truth is that you cannot trust them. Manufacturing tolerances as also properties of glass, proper alignment, etc. affects the lenses so that one never gets the theoretical performance. Therefore it's more fair and truthful to see the measurements from real lenses. Also, I should add that Sony isn't even that bad as some other manufacturers that regularly publish MTF-diagrams with lines peaking at 100% – only it's just that it is physically impossible due the diffraction limitations of optical systems. Kind of wrecks their credibility. ZEISS is a rare exception, because their MTF comes always from the real lenses.
What I always do when ZEISS announces a new lens is that I compare it to other lenses in their catalogue. This is a good way to position the new lens compared to others (and of course to speculate how good ZEISS has succeeded this time). So here's the Batis 2/40 CF compared to Batis 2/25 and Batis 1.8/85 which present the obvious peer group.
Wide open and at the center of the frame the Batis 2/40 CF is the best of these three lenses. The performance is very similar to Batis 1.8/85 which is a compliment to Batis 2/40 because being a moderately wide lens it is more difficult the design than the short tele lens. Being familiar with the Batis 1.8/85 performance I think this is great news as it is about the best lens I've ever tested regarding wide open performance. I'm also happy to see that wide open Batis 2/40 is clearly better than the Batis 2/25. Don't get me wrong, the Batis 2/25 is also one of best wide angles you can get for Sony Alpha cameras (the new Sony 1.4/24 might be better), but the center resolution is clearly better with the Batis 2/40. Stopping down to f/4 all three become very similar with each other. Those who are already familiar with the Batis performance should be very well home here with the new Batis 2/40 CF.
So, the Batis 2/40 CF seems to fit very nicely to Batis lens family, but what about the other ZEISS lenses, like some similar from the Milvus lens family. Okay, so here is Batis 2/40 CF compared to Milvus 1.4/35 and Milvus 1.4/50.
The Milvus lenses are one stop faster so it's a kind of unfair comparison because stopped down they would do better, but still one can only admire the wide open performance of the Batis 2/40: plenty of contrast and resolution. Stopped down to f/4 the Milvus 1.4/35 takes a winning position here as it should because it is a large and uncompromised lens weighting a whopping 1174 g (quite a difference compared to 361 g Batis). But then compared to Milvus 1.4/50 the Batis has a very similar performance.
Every now and then I hear people claiming that Otus & Milvus represent ZEISS's premium lenses while the autofocusing Batis and Touit are only 'almost-premium lenses' (to put it nicely). This comparison doesn't support it. Sure there are some different design limits with different lenses, but unlike other companies like Sony, Canon or Nikon, ZEISS doesn't categorize their lens families similar way. Everything they do represents the professional lenses because it's in their brand and they don't do separate product lines for consumer lenses. If in doubt, they a look at the Touit MTF-diagrams, very similar looking curves there.
Ok, that's about all I'm going to say about the Batis 2/40 CF MTF-diagrams, but how does the optical performance look like in practice, you might wonder? Come back tomorrow and I'll show you!