Ok, let's talk a bit about bokeh then. For many this is, together with sharpness, one of the most interesting aspect of a new lens. 'Is the Batis 2/40 CF's bokeh good?', I hear many of you asking, but reducing such a complex subject into a one single-line question is a difficult approach. To be honest, I've been avoiding this topic because (1) it's difficult to discuss the bokeh with terms-explicit-enough; people have different expectations, aesthetics and words. Another reason avoiding this topic until now is that (2) it's difficult represent the bokeh quality of some particular lens with just few pictures. The best way evaluating it would be to use the lens yourself within the context of your own photography, but this sort of laconic statement doesn't fit into mission of the this blog – so I will share some of my thoughts about the bokeh.
But first, let's get a bit philosophical here. Photographers love to talk about which lens has a good bokeh and which does not. I totally understand this discussion, but I also honestly believe that one should not generally try to find the lens 'which has the best bokeh', or step into a pitfall of ranking different lenses based on how blurry background can be achieved with them. The problem is that this sort of approach makes the bokeh a single dimensional character of the lens (good vs. bad) and ignores the fact that it is also an aesthetic judgment. Convoyed by this kind of discourse many photographer approach bokeh from the point of view of optics, ie. what happens inside the lens. The characteristics of bokeh are cut up to technical attributes like the shape and structure of the aperture iris, transition between focus and out-of-focus areas, characteristics of the highlight discs, and so on. Still, the bokeh and its characteristics are largely dependent of the circumstances one shoots, and every lens can be taken to situations where the bokeh rendering falls apart.
I would like to think that the bokeh is also an aesthetic attribute of a particular picture. Instead of all technical details, this sort of approach emphasizes the aesthetic nature of the bokeh. We shouldn't just ask if the bokeh is distracting or not, but how does it add into picture. For example, personally I'm not too interested about totally diffused bokeh with blobs, bubbles and all (something to which this initially a Japanese term refers to). I much prefer a more simple subject separation where the background has some blurred gradations and still contain cues about environment. Of course a lens and it's optical structure plays a big role here, I'm not dismissing all the technical stuff, but this sort of approach also reminds that there are no magic lenses that can create perfect bokeh all the time (how boring would that be) and on the other hand any lens can be used to create bokeh that can support picture aesthetically.
So what to expect from the Batis 2/40 CF's bokeh? Well, it is a moderately wide focal length, so one should not expect a super diffused bokeh as none of the 35mm lenses nor the 50mm lenses provide that (you needs at least a 85mm lens for that). But this is not to say that these lenses don't do bokeh. On the contrary, the 35mm and 50mm lenses are known for certain kind of classic aesthetics which speaks to many people – not to shallow depth of field but not too extended either. Here's a small comparison so it's easier to put the Batis 2/40 CF into context of other focal lengths and apertures (the formula used here is simple, just divide focal length with the maximum aperture, it will give you a rough idea of bokeh potential):
ZEISS Batis 2/25 | 12,5
Sony 35/2.8 ZA | 12,5
Sony 24/1.4 GM | 17,1
general 35/1.8 | 19,4
ZEISS Batis 2/40 CF | 20
Sony 35/1.4 ZA | 25
ZEISS Loxia 2/50 | 25
ZEISS Batis 1.8/85 | 47,2
The Batis 2/40 CF offers quite nice bokeh potential adding a touch more than the general 35/1.8 lens, but less than more heavier 35/1.4 lenses – interestingly the bokeh potential resembles more of a 35mm lenses than 50mm. In practice I think it's very sufficient as it enables subject separation even a bit further away and if you want to melt your background completely it is certainly possible at close distances.
Largely speaking the Batis 2/40 CF is a consistent and a reliable lens when it comes to bokeh. One could describe the bokeh 'creamy' meaning that out of focus points of light will often turn into soft indistinct blobs that melt into each other. The consistent also means that one very rarely sees any degradations, but of course any lens can be put into conditions where the bokeh will eventually fall apart. But in this regard the Batis 2/40 CF is very easy lens to shoot with and it doesn't offer nasty surprises. At its best, at close range, the bokeh is quite painterly looking and gives pictures a nice timeless look – perfect for many wedding photographers and such. With the extended distances the bokeh of course dilutes, but still retains contrast and doesn't become hazy. Between the close range and extended distance the lens shows a very good subject separation with excellent contrast.
Unlike the Batis 1.8/85 (for example) the Batis 2/40 CF has three aspherical glass elements within it which can, in theory, cause some onion rings. I've seen a few with some strong highlights like led lights and such, but mainly the bokeh blobs are very clean and consistent, meaning they don't have distinct edges and they also keep their shape quite nicely as well. One can see them flattening a bit at the corners, but this generally happens with many 35mm and is expected. In right circumstances the bokeh blobs show longitudal chromatic aberrations, but definitely less than with the Batis 2/25.
All in all the Batis 2/40 CF succeeds in creating a quite pleasant bokeh which of course also depends on the subject background. Together with the excellent sharpness at focal plane the pleasant and 'creamy' bokeh creates a certain contrast between focused and out of focus areas – something which I think gives the Batis 2/40 CF its distinct rendering characteristics. Compared to other Batis lenses (Batis 2/25 & Batis 1.8/85) the rendering characteristics are very similar, but with the Batis 2/40 CF they perhaps the most consistent.
So, there you go, my thoughts about the bokeh. Does the Batis 2/40 CF automatically give you a perfect bokeh for your pictures? Or course not, because one has to work with bokeh, just like with composition and light. But the Batis 2/40 CF has great potential if you like your bokeh creamy. So, yes the bokeh is important but it is not more important than other elements in picture. I could as far as to say that when the subject is strong enough, the character of the bokeh will be largely meaningless. So, always look for the strong subjects first and only after then let the bokeh add its magic to the picture at the background - with its consistent bokeh the Batis 2/40 CF is certainly capable of that.