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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.




Day #34 - nonagons, do they exist?

Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2, 1/3200sec, ISO100, raw Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2, 1/3200sec, ISO100, raw
Photograph by Toni Ahvenainen

Yesterday I wrote about the improvements the new firmware-update brings to Batis 2/40 Close Focus ability. And as promised, today I will concentrate on a special case related to close focus: the nonagons. What nonagons you might ask? If you are not familiar with the word, it points to a special nine faced polygon shape called nonagon.


So, what I mean with the nonagons? Because the Batis 2/40 CF closes aperture down a bit automatically when working at close focus distances, the highlight bokeh balls get, in some certain cases, a bit angled. This happens because the aperture doesn't stay fully open at the maximum aperture (f/2), so the bokeh balls might reveal the structure of the aperture mechanism, ie.  nine-sided polygons, also known as nonagons. When the Batis 2/40 CF was first introduced some expressed their concern related to nonagons: they were seen as distracting detail regarding lens rendering, although there were also many who thought that it was no issue really. Since then the Batis2/40 CF Close Focus ability has been contaminated with some nonagon-fewer, but I would like to argue that the whole nonagon thing is a bit exaggerated because in real life one doesn’t see them as much as one would think by reading various internet forums. But let’s get to the basics first.

Why does the nonagons appear and how often they appear? Well, first of all (1) you need to work with the maximum aperture, otherwise you have already chose to close down the aperture and the Batis 2/40 CF behaves just like any other lens. Secondly (2) this only happens when you are focusing at pretty close range, let's say about 1 meter. And the most important factor is (3) that it really depends on the scene whether you have clear point-like highlights there that have enough contrast compared to background. In many situations the nonagonal shape of the bokeh balls doesn't reveal themselves even if you are working with the maximum aperture at the close range. But then again, there definitely are situations where it can happen (as I'm about to show you). But to get to the point: it doesn't occur automatically because there a lot of different factors at the play. 

How does the new firmwire-update affect this behaviour? The new firmwire-update (Ver 02) definitely affects this behavior because the lens now only closes its aperture only a one stop at close focus distances (instead of two stops of the previous fw-version). This means that the phenomenon of nonagons is reduced with the new firmwire-update. How much you might ask and I would have to answer that I really don't know the real answer since there are some much different factors causing it. However, I can make an educated guess that with the new firmwire-update the nonagons will quite likely only show themselves when working below 0.5m (or so). This estimation is based on the fact that with the new firmware the aperture gets closed only half of what it was with the previous version. This means that the aperture blades will close down to 'the nonagon-point' later than previously, which also means that the nonagons must appear later. How much later? About half later would be an appropriate guess.

Now, to put this information to use in real life I tried to come up with images that would show some nonagons. I'll have to say that it is harder than what one might think because not every shooting scenario have the same amount of potential for this to happen. Now, someone might point out that I could have used some Christmas tree lights, led-lights or similar to test it easily, but there's a specific reason why I didn't want to go into that direction (hold that thought, I'll explain it soon). Instead, I went to the same bridge with a lot of locks that I've been using in this project before (see day 02) and thought that with the bright sunlight I could easily introduce some nonagons into my images. But this turned out to be much harder than I thought. As you can see from today's picture I build the composition so that there would a lot of locks and point-like highlights in the background of the picture and shot it with aperture fully open at f/2 at the minimum focusing distance. This brings the bokeh balls but it really doesn't show any clearly defined nonagons. To be honest I had to work a bit for the nonagons and yes, finally I managed to introduce some into my images, but it took a bit of effort since shooting wide open and minimum focusing distance isn't enough to introduce them - one still need to have a pretty specific situation. So, here's the specific situation what I'm talking about. Shooting at a right angle I could compose a single point-like highlights to very dark background which then, finally, introduced the nonagons:

Sony A7III & ZEISS Batis 2/40 CF – f/2, 1/4000sec, ISO100, raw Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2, 1/4000sec, ISO100, raw
Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2, 1/4000sec, ISO100, raw Photograph by Toni Ahvenainen

Sony A7III & ZEISS Batis 2/40 CF – f/2, 1/4000sec, ISO100, raw
Photograph by Toni Ahvenainen

Now, there's a specific reason why I wanted to show the nonagons in this way: first the image with the nonagons and then the second one without them. With these two pictures I hope to show you how much little change in point of view/focus point can change the situation (between these two pictures I’ve hardly moved). I believe this portraits the whole 'nonagon-issue' in a right light: (1) most of the time you just don't see them at all, (2) and to reveal themselves you often need a pretty specific situation. So, for the most users 'the nonagon-issue' is not an issue at all. Now, I could have described the same optical phenomenon with the led-lights, Christmas lights or something similar, but I think it would have led to a false interpretation of the situation. For example, I've seen some review sites trying qualify lens bokeh with Christmas lights by showing how the bokeh balls might flatten differently between different lenses. There's of course a factual difference between the lenses, there's no denying that, but these sort of pseudo-scientific tests often lead users to a wrong interpretations by exaggerating the differences. In real world the lens might perform very very similarly, but looking at these tests one might come into conclusion that some of the lenses have 'serious issues' or something similar with their rendering. This is exactly the slanted approach I wanted to avoid here and that's why I decided to describe the nonagons through a true real life experience to give you a better understanding of the situation. So, in short it is possible to have some nonagons in your images because the Batis 2/40 CF closes down its aperture a bit when working at the close distances, but the new fw-update definitely reduces this effect and makes it even more rare in real life shooting situations. Only for those who plan to use the Batis 2/40 CF only for macro photography, this might be an issue, and for them it might be more appropriate to check out some dedicated macro lenses instead. For the rest, the nonagons are hardly an issue and they shouldn’t overshadow the fact that in general the Batis 2/40 CF performs very nicely with close focus shooting scenarios.