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Three lenses: a look at bokeh, depth of field and geometry

What’s out of focus is just as important as what’s in focus, but often it’s an afterthought. Come see why it shouldn’t be.

Some people take time off during the holidays. I borrow a half million dollars worth of camera and lenses and shoot whatever comes to mind. It’s a sickness, but an enjoyable one.

In this article, I wrote about the experiments I carried out in my living room with an Alexa LF and three kinds of lenses: ARRI Zeiss Ultra Primes, ARRI Signature Primes, and a single ARRI Zeiss Anamorphic Master Prime. In this article, I’m going to start out in the same place but travel further afield. The goal: shoot a variety of settings with three different types of lenses and define the differences.

I’m less concerned about how these lenses look at the point of focus and more interested in how they render backgrounds. Bokeh, or the quality of the out-of-focus image, has a strong impact on any image, and yet we are often not consciously aware of its effects. We naturally look at whatever is sharpest within the frame, but bokeh can direct attention to the subject or distract from it. Bokeh can be hard, soft, colorful, distorted, high resolution or low resolution. It’s the backdrop against which stories unfold.

Let’s take a look at some examples.

Bokeh is always most dramatic when a lens’s aperture is wide open, so that’s what I did here. A small antique statue serves as the focal point and a Christmas tree provides some reference highlights.

Anamorphic bokeh is very distinct. This 40mm Master Anamorphic lens is really two lenses in one: a 40mm lens in the vertical dimension and a 20mm lens in the horizontal dimension. The creates the 2:1 squeeze found in traditional S35 anamorphic lenses. Because the vertical 40mm axis goes out of focus more quickly than the horizontal 20mm axis, the highlights take on an oval shape as they blur more quickly in that dimension.

Master Prime anamorphic lenses are more complex than typical anamorphic lenses in that the squeeze happens a little at a time across a number of different elements, rather than all at once due to a cylinder placed at the front or rear of the lens. This ensures that the squeeze is consistent as focus changes. In the distant past, anamorphic lenses suffered from the “anamorphic mumps,” where close focus had a tendency to make things appear wider, such as faces. There are many tricks to get around this, but ARRI’s method of distributing the 2:1 squeeze across a number of internal elements is the most complex and effective.

Master Anamorphics are great lenses for a clean, crisp look with little-to-no focus breathing and great flare control while retaining the characteristic anamorphic oval-highlight look.

Note: I cropped the 2.39:1 image to 16:9 to facilitate comparison with the other lenses.

The 32mm ARRI Zeiss Ultra Prime is the closest match I had in my kit to the 40mm Master Prime. In UHD mode on the Alexa LF, the portion of the sensor used for capture is exactly the same height regardless of whether spherical or anamorphic lenses are used. This is not the case in film, where Academy aperture and anamorphic frame sizes are different heights. In this case, a 40mm Ultra Prime and 40mm Master Anamorphic prime cropped to 16:9 would have matched exactly, at least in frame height.

Sadly, I didn’t have a 40mm Ultra Prime, so the 32mm will have to do.

Ultra Prime bokeh isn’t bad. It’s not perfect, which gives it a vintage feel. Modern lenses favor soft highlights that are evenly illuminated, but vintage lenses are a little sloppy. Highlights may have rough edges due to chromatic aberration, or hot and/or dark centers due to spherical aberration. These Ultra Prime highlights look reasonably modern, but to me, they also have a hint of 1980s ARRI Zeiss Super Speed in them. There are some images later in this article that better illustrate this.

ARRI Signature Primes are engineered to be smooooooth. The newly-introduced LPL standard lens mount gives optical designers a lot of freedom to eliminate chromatic aberration, which takes the edge off most images, sharp and soft. Also, Signature Primes are designed to be telecentric, which has a smoothing effect on bokeh, although no one knows exactly why.

When shot wide open, Signature Prime highlights are “trimmed” to create a swirling effect around the edges of the frame that drives the eye inward toward the action. Stopping down to T2.8 eliminates that effect and yields round, clean, bokeh.

Signature Prime bokeh blends like nothing I’ve seen in any other lens. Even stopped down, highlights and textures are smooth with gentle transitions.

Bokeh is not just about highlights. It’s about resolution as well.

As an anamorphic lens with a 2:1 squeeze is two lenses in one, depth of field will be less in the vertical axis than in the horizontal axis. Strangely, this means vertical lines will be rendered as sharper because, when they go out of focus, they stretch vertically, overlapping themselves. They end up as one tall blur. The gaps in between are sharper and have more contrast because they are less blurred.

That’s the difference between having a 40mm lens in one axis and a 20mm lens in the other. They drift out of focus at different rates.

A spherical lens, however, softens equally in two dimensions:

The Signature Prime frame was captured in Open Gate 2.39:1 to best match the anamorphic frame. The blinds are much softer than in the anamorphic image. That’s because they are blurred in equal amounts both horizontally and vertically (35mm tall by 35mm wide). The anamorphic lens blurred them half as much horizontally (40mm tall by 20mm wide), which made the gaps between the blinds appear sharper.

In this article I photographed some vases with human faces to illustrate how these different lenses rendered shadows and flesh tone. I also shot some out-of-focus images to show that anamorphic lenses are not always as soft as we might think:

I can still see a lot of detail in the anamorphic image, especially where the detail runs vertically: the neck of the tall gray vase, for example, or the handle on the orange vase, or the noses. The Signature Prime blurs every axis equally to create a much softer image. (The 7mm difference between the anamorphic and spherical lenses shouldn’t cause a dramatic difference between the two. Most of the spherical lens’s increased blur is due to its defocusing equally in both dimensions.)

This brings up an important point. Given these conditions, the spherical lens makes backgrounds softer than an anamorphic lens of the same focal length, but the depth of field is exactly the same. There’s no reason to fear large format if you’re already shooting anamorphic.

Having grown tired of shooting in my living room, I packed up the car and drove out to the rural Northern California coast.

Don’t tell my boss.

There I found a wonderful row of old mailboxes.

The anamorphic bokeh is wonderfully smooth, but still preserves vertical detail and contrast. The letters “304” read clearly on the mailbox because the vertical strokes of the numbers don’t blur as much as the horizontal strokes. The background highlights have taken on the characteristic oval shape of an anamorphic lens.

The Ultra Prime bokeh has a harder edge to it. I consider this a “vintage” look, and it works great for some things. It’s slightly sloppy, and renders soft backgrounds as having some texture. Highlights on individual leaves are still visible and compete with each other.

The Signature Prime is incredibly smooth. Highlights show no hard edges at all. I can see subtle textures, but they blur together as if I’m looking at a watercolor pointing. The Ultra Prime is a pointillist painting by comparison, with the anamorphic image appearing slightly impressionistic.

I was curious as to whether these characteristics remained when the lenses were closed down by two stops, so I backed off on my neutral density filtration and shot another round.

The bokeh characteristics carry through in each image. The Master Anamorphic lens still feels a bit like an impressionist painting. The Ultra Prime feels like a pointillist painting. And the Signature Prime still feels like a very smooth wash of watercolor.

There are worse ways to spend a winter day.

I’ve got another set of stills to show you, and then I’ll toss in a couple of video comparisons. I found this vista at the Fitzgerald Marine Preserve in Moss Beach, CA. Focus is placed on the post in the center of the frame.

The Ultra Prime shows a little vignetting in the corners but otherwise holds up quite well to the others. The Signature Prime pops the warm hues a bit more, but that’s a part of its design. (The light doesn’t match perfectly in these images due to changing conditions.)

The Ultra Prime’s bokeh has more texture to it than the other lenses, at least when focused at this distance. It’s not unusual for the quality of a lens to change based on focus distance, so it isn’t surprising that bokeh changes as well. At close focus distances, the bokeh appeared smoother (see the statue images at the beginning of this article).

A close look at the rocks on the beach shows that the Ultra Prime blurs detail while retaining the overall texture of the setting. This is what I consider “classic” or “vintage” bokeh: it’s not engineered to recede into the background, but rather is what the optical designers could manage at the time. Optical engineers generally pay attention to the point of focus first, and the quality of the out-of-focus image is secondary.

The Master Anamorphic has a little bit of a vintage feel as well. The highlights at the top left show anamorphic’s telltale vertical distortion but also exhibit a “smeary” quality that I quite like. The rocks on the beach retain detail because anamorphic lenses soften detail vertically more than horizontally, so the gaps between the rocks retain contrast on the horizontal axis.

Vertical objects are sharper than horizontal objects because vertical lines overlap when stretched, but horizontal lines blur and increase in size. The Ultra Prime feels harder, even though it blurs equally in both dimensions, because its bokeh has a harder quality.

The Signature Prime is the softest of all. The highlights at the top left are evenly illuminated. The rocky promontory shows hard edges in the other images that I don’t see here. The textures on the beach blend nicely.

This is a very different feel from the other lenses. It’s smoother and gentler. Once again, this feels like a watercolor painting to me. And, counterintuitively, this image is softer than that of the Master Anamorphic, even though the focal lengths are nearly the same. One can shoot anamorphic in LF UHD mode, or spherical in LF 2.39:1 (using the full width of the sensor) and capture two very different looks at similar focal lengths—and, technically, with the same depth of field.

Lastly, I thought it would be fun to see if there are any geometric differences between the anamorphic and spherical lenses. I had a sense that they might render depth differently.

I grabbed two similar shots as the sun set: one with the 40mm ARRI Zeiss Master Anamorphic, and one with the 35mm ARRI Signature Prime. I then matched the frame sizes in DaVinci Resolve and flipped back and forth between the images on the timeline. The differences became very clear.

The Master Anamorphic renders space differently. The trees at the edges of the frame feel farther away. The vertical anamorphic stretch makes them thinner by comparison to the spherical lens, and therefore they feel more distant. It’s interesting that the lens pulls trees into the frame that aren’t visible in the Signature Prime image.

There’s a horizontal branch at the top right that doesn’t change much between the two lenses, but the vertical trees in the background are wider and softer in the Signature Prime image. Once again, anamorphic blurs horizontal lines more than vertical lines, but spherical blurs both dimensions equally.

In this case, I like the flatness of the Signature Prime. Epic films of the 1950s, 1960s, and 1970s were often shot on large format film with spherical lenses, so they felt flatter than anamorphic films, which were largely shot on 35mm film and showed more distortion. This simple shot has that same epic feel.

This last video shows the overall shape of the two lenses.

The anamorphic lens draws in the sides, whereas the Signature Prime has a flatter feel. Also, I can see the vertical branches more clearly in the anamorphic image (particularly at the right of frame) whereas the spherical image renders background detail as softer.

I’m not saying that one of these looks is better than another. Artistry doesn’t work that way. Rather, it’s important to understand exactly what our tools do so we can decide when best to apply them. Lens characteristics interact in complicated ways, and I find it helpful to isolate these characteristics in order to examine them more clearly. It’s also helpful to compare lenses, as any image on its own may look just fine. It’s when we compare looks that we become aware of their differences and subconscious effects.

Art Adams is Cinema Lens Specialist at ARRI, Inc. He was a freelance director of photography for over 26 years. You can reach him here.

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Art Adams is a cinema lens specialist at ARRI, Inc. Before that, he was a freelance cinematographer for 26 years. You can see his work at http://www.artadamsdp.com. Art has been published in HD Video Pro,…