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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.




Filtering by Tag: Banknote

Day #33 - close focus revisited

Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2, 1/160sec, ISO1250, raw Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2, 1/160sec, ISO1250, raw
Photograph by Toni Ahvenainen

As I told you yesterday the new firmwire-update for the Batis 2/40 CF corrects the earlier Eye-AF issue and the Eye-AF now works very well indeed with the lens. Another aspect of the firmwire-update is related to way lens automatically closes the aperture when working close to minimum working distance. In fact, this caused a quite a bit controversy in the net when the Batis 2/40 CF was released in the first place, but I would like argue, that one reason for this was the confusing and mixed reports describing the actual aperture behavior – and ZEISS could have handled the communication better as well. The thing is that the Batis 2/40 CF closes its aperture a bit when working at close focus distances, to ensure high image quality, but I’ve seen so many mixed reports regarding at which distance the actual closing starts. For example, some have claimed that the f/2 wide open aperture is only kept at the infinity. Then I’ve also seen some users stating that the lens starts to close down about 65 meters, or 34 meters, or 16 meters. I myself said that the closing in starts about 1 meter. Why so many different figures? I believe it is because (with the original firmware version 01) the aperture blades do react a little (very subtle) somewhere about those figures, but I would argue that the real closing (that affects exposure) really happened only at about 1 meter or so. So, with the previous version of the lens the aperture closing was a kind of logarithmic smooth curve (probably to smooth out video use of the lens), but it surely did cause some critical reactions. However all that is now past because the new FW-version 02 changes the aperture behavior quite a bit.

The new FW-version 02 keeps the aperture constant from 0.65m to infinity. This means that if you have set the aperture, for example, to f/2, it will stay there whenever you work with distances greater than 0.65m. Therefore, at the typical portrait distances the Batis 2/40 CF will keep the aperture fully open and you’ll get those dreamy portraits and other stuff no problem at all. At the infinity, the wide open aperture is of course f/2 and nothing else, I see no movement what so ever with aperture blades.

Now, the aperture will start to close down automatically only when you focus at distances below 0.65m. This means that the aperture will be closed a bit at close distances to maintain maximum image quality. How much, you may ask? At maximum, which happens only at the minimum focusing distance 0.24m, the aperture is closed down exactly one stop (for example from f/2 to f/2.8). In practice most of the close focus shots will probably happen between 0.24m – 0.65m, so the aperture will close down less than a stop (for example, from f/2 to f/2.5).

Additionally, the lens does not change the aperture at all if you are using anything between f/2.8 – f/22, regardless of the focusing distance. In other words, the automatic closing of aperture only happens if you are (1) focusing closer than 0.65m and (2) are using aperture greater than f/2.8. Here's a nice table from ZEISS which describes the behavior quite nicely:


All in all, I would say that the automatic closing of the aperture happens at pretty limited shooting conditions, and when it actually happens, the compromise is rather small. ZEISS received a quite a bit critique because of this behavior (or the behaviour of the previous firmwire-version), and while some of it was justified, some was also a bit overblown. For example, some users saw it as a way of ‘cheating’ or ‘patronizing’ the users, which is of course an exaggerated reaction to a neutral design decision. It’s there for maximizing image quality and enabling the close focus ability, and if any other lens, like the very good Sony/Zeiss FE 50mm F1.4 for example, would offer a similar close focus ability with a similar compromise, I would gladly take it (it doesn’t take anything away from the lens). But none of the standard focal length lenses really offer anything like this and feature-wise they are limited to lesser magnification ratios. So, I honestly think it’s a good and wisely chosen compromise to extend the shooting envelope for the lens, and the lens is also designed to deliver great optical performance at these distances. So, in my eyes it’s all good.

However,it is certainly true that the Close Focus feature was also a little bit rushed to the markets. The proof is in the details: with the earlier firmware (ver01) the lens would also stop down even with apertures smaller than f/2.8 and f/4 (for example, the lens could stop down two stops from f/5.6 to f/11 at minimum focusing distance). This was surely an overlooked aspect and not polished to the German standards (shame on you, ZEISS). But with the critical discussion this aspect of the lens is now changed and polished. So, all in all I’m glad that ZEISS decided to reconsider the aperture behavior and the Batis 2/40 CF surely feels much more ready now.

In fact so ready that I think, the ‘aperture-gate’ really overshadowed the most important thing related to close focus ability: it increases the versatility of the lens and the optical performance is, at its best, truly superb at close focus distances. Now, that I’ve seen what is possible at close focus distances I feel much more demanding with other lenses. But I have to admit, that I was a bit concerned if the new FW-update would decrease the image quality because the lens now only closes down a one stop instead of two stops. I expected this maneuver would introduce some chromatic aberrations, but I haven’t really seen them at all and the lens performs almost as good as with the earlier FW for all I know. The only thing I can see is that there emerges a little drop of contrast when working at f/2 at the minimum focusing distance (which means true f/2.8). Not a deal breaker at all. If anything, the ‘aperture-gate’ tells us something about how high the image quality standards ZEISS has – maybe even too high as it seems many users wanted to shift the lens behavior to another direction. But again, we are not losing anything and if you want to maintain 'the original ZEISS standard' or work with the best possible image quality, just close the lens down to f/4.

Sony A7III & ZEISS Batis 2/40 CF – f/2.0, 1/160sec, ISO100, raw Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2.0, 1/160sec, ISO100, raw
Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/5.6, 1/100sec, ISO250, raw Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/5.6, 1/100sec, ISO250, raw
Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2.0, 1/400sec, ISO100, raw Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2.0, 1/400sec, ISO100, raw
Photograph by Toni Ahvenainen

To estimate the optical performance at close focus distance I devised a test with a simple 5 euro paper money. For European users this will provide also a good measure of how close can you get with the Batis 2/40 CF - just dig out a 5 euros and see if you can spot the same details from the actual money. I can't say this is a definitive test of Batis 2/40 CF optical quality because creating a test setup like this one would need a great precision to get the subject as straight as possible - even the smallest misadjustment will wreck some of the results. Another, and maybe more interesting, challenge was Adobe Photoshop and Lightroom which both refused to export the image because the image is about paper money. I kid you not, much to my suprise I got the error mess saying:


I was as surprised as you might be right now and it became almost impossible to get the image out of the problem. I tried to get it out in smaller sections, but it didn't work either. At the end the Microsoft Paint (!) came to rescue and finally I got the image out of the Abobe programs. I have to say this was a pretty interesting challenge and felt a bit like Matrix. But okay, let's take a look how the Batis 2/40 CF actually performs at the minimum focusing distance:


As you can see at the f/2 (true f/2.8) the details are already quite good at the center. Quite nicely the details a good at the corners as well, but the midfield is a bit behind here. This is already a pretty good performance which you can verify yourself if you have a 5 euros bill - just try to find the same text there at the bridge and you will see how incredibly small it is in real life. So, not a bad performance at all. Stopping down to f/2.8 doesn't change a thing, because the aperture doesn't change at all. And only when you stop down to f/4 the contrast gets a bit better, especially at the midfield, but the corners are also very good. After f/4 I don't see much of improvement and the lens seems to perform best around f/4 or f/5.6. At the f/11 the diffraction kicks in a very little. All in all, it's a very very good performance, and if you want, you can see why ZEISS wanted the lens to operate at f/4, because that's where the best performance is. Another interesting observation is that throughout the whole aperture range there is no vignetting at all. Like I said, a very good performance.

Ps. But what about the nonagons I hear you crying! I’ll address those separately tomorrow!