Bokeh Effect

[Haitham Lawati]

Schneider Cine-Xenar III Prime Lens is one of the rare lenses that comprises an 18-blade iris. Does anyone think that this lens will provide more pleasant look of seamless bokeh compared to other cinematic lenses that have less number of blades?

[Jon Fairhurst]

The nature of Bokeh is complex and depends on the glass as well as the aperture. I have an old medium format Bronica with a Nikkor lens that makes "onion ring" bokeh - the shape is round, but the circles are not filled in.

That said, more blades are more likely to produce smooth, round bokeh. Note that some lenses use straight blades while others are curved.

[Haitham Lawati]

Thanks for your response. How would you compare this lens to other cinematic PL lenses in terms of Bokeh's beauty such as Carl Zeiss, Fujinon. Canon, Angeniux, etc which have blades less than Schneider?

[Jon Fairhurst]

Unfortunately, I haven't used that lens family nor have I studied images from it, so I can't offer any specifics.

Another theoretical advantage of more blades is more accuracy and consistency at very small apertures. I learned about this issue when making f/16 timelapses with DSLRs. Lenses with electronic apertures open and close for each shot. If the position of the blades changes slightly from shot to shot, one gets flicker. The shape of the bokeh can also change when there are few blades as they don't always close symmetrically. A solution that I now use is to hold the DOF button and to partially unscrew the lens as this locks the aperture to a specific, fixed position.

In the case of the Schneider Cine-Xenar III Prime Lenses, you won't have the timelapse flicker issue, but you might see a slight advantage in consistency when stopping down after manually changing the aperture. With so many blades, the error from any single blade will be minimized. Then again, this might be "over-polishing the apple". Shot to shot consistency due to aperture errors, aside from timelapse flicker, probably isn't in the top 1,000 of real-world problems that filmmakers face.

[J. David Pope]

Originally Posted by Haitham Lawati

Schneider Cine-Xenar III Prime Lens is one of the rare lenses that comprises an 18-blade iris. Does anyone think that this lens will provide more pleasant look of seamless bokeh compared to other cinematic lenses that have less number of blades?

Haitham- I used to think that more blades = more rounded flare and more creamy bokeh but some folks more educated on lens tech than I have informed me that this isn't always the case. There are other factors in the mix. Some lenses have curved iris blades. There was even a lens with two irises!

Maybe someone else can chime in here but a lens such as the SLR magic only has 12 blades compared to the 18 on the Cine-Xenar yet the SLR has a far more creamy bokeh. Generally speaking, really fast glass has great bokeh. So-called "hyper" primes such as the Nokton's.

Back to the Cine-Xenars, I saw a comparison to the Cooke MiniS's and the Cookes had octagonal flares while the Xenars were much more rounded and without corners. I gather it is this perfectly round flare / round bokeh that you like. Look online and you will find some videos with examples of the flare / bokeh of the Cine Xenar glass.

I was pondering the Cine Xenars vs the Xenons. What decided it for me, outside of cost, is the physical size of the lenses. The Xenars are massive. The Xenars are obviously a higher-end lens. They do not breathe at all as they are tele centric.

Peculiarly, as a result of numerous factors, the more expensive Xenars do not cover full frame while the less expensive Xenons do cover full frame.

In summary, after much rambling, more blades does not necessarily equate to more pleasing bokeh or more "rounded" bokeh. And some actually prefer the more octagonal, more "geometric" bokeh in the way that people like the oblong flares of anamorphic.

[Haitham Lawati]

Thank you very much for your reply. It was really informative and comprehensive.
I do understand from your viewpoint that different lenses provide different styling and artistic effects for bokeh, and the matter of preference is subjective.

[Jon Fairhurst]

Bokeh has two main components: shape and fill.

The shape is important when the aperture is relatively small and can be seen in flare patterns.The shape is almost purely based on the iris blades.

The fill can be flat, ring-like, mottled, or have any number of "looks". This is based on the glass and coatings more than the iris. The fill can be clearly seen when there are small lights that are slightly out of focus at medium apertures.

In my experience, it's the fill that is critical. Hard rings can be really ugly when there are many highlights in the background. When the shot has a very shallow depth of field and the background is heavily blurred, it's the fill that matters. A smooth bokeh fill will make a smooth background. Rings can create distracting sharp lines in blurred backgrounds.

If one is shooting with small apertures with flare, shape is an important factor. The shape can be an artistic choice. Fill is an important factor across the board. Fill can mean the difference between "beautiful" and "ugly" for certain shots.

The bottom line is that the number of blades doesn't tell the story. One needs to look at images. And pay at least as much attention to the fill as the shape.

[Haitham Lawati]

Which lenses, from your experience, provide impressive fill for the bokeh?

[Jon Fairhurst]

I've never done a lens by lens analysis. I recommend identifying lenses of interest and seeking example images.

Here is an excellent review of bokeh: Bokeh

Figure 6 shows the problem with "doughnut-shaped bokeh fill". It can make double lines and other ugly artifacts. I get this result with my Nikkor 75mm lens on my Bronica S2A medium format film camera. I can still get wonderful photos from that camera/lens, but I have to avoid high contrast in out-of-focus areas. I generally use the smallest possible aperture when using that setup.