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30 Days of Batis 2/40 CF
A Batis adventure and a personal photography scratch book with a creative touch.
Sharing a new post every day for the next 30 days.

Journal

 

 

Day #13 – the modulation transfer function day

Toni Ahvenainen

Sony A7 & ZEISS Batis 2/40 CF – f/5.6, 1/60sec, ISO125, raw Photograph by Toni Ahvenainen

Sony A7 & ZEISS Batis 2/40 CF – f/5.6, 1/60sec, ISO125, raw
Photograph by Toni Ahvenainen

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.

mtf-02.jpg


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.

mtf-03.jpg


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!