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Art Adams is Cinema Lens Specialist at ARRI, Inc. You can reach him at ARRI’s Burbank, California office.

The two master cameras used 5:1 zooms, and the two wing cameras used 10:1 zooms. Our tests showed that the 10:1 zooms underexposed the image by 2/3s of a stop toward the long end of their range, apparently due to vignetting. The lesson I learned was that lens exposure markings couldn’t always be trusted.

I ran into this again as I transitioned from camera assistant to DP and found myself working in the video realm. I quickly learned that broadcast zoom lenses showed extreme port-holing at the long end of their range. As I zoomed in, I could see a ring of shadow advance from the outside edges of the frame toward the center, with the upshot that the center of the lens remained consistent in exposure but the edges dropped off considerably.

This was an important discovery. I didn’t know how important until recently.

Upon starting with ARRI as Cinema Lens Specialist, I shot a lot of tests to see how our new ARRI Signature Primes compared to other lenses. I found a lot of differences, but the most baffling was that they were almost always brighter than other lenses, often by a half stop or more.

I was baffled. How could Signature Primes be brighter than other lenses at the same T-stop? Were our T-stop markings mis-calibrated? Are we focusing the light differently on the sensor? Are our coatings somehow making the optics more efficient? None of these made sense. My assumption was that we must be doing something that bordered on the magical that changed how they transmitted light, or gave them a different dynamic range curve, because other lenses appeared to be consistent in exposure and Signature Primes were always different.

As it turned out, all of this was completely wrong.

I got in touch with some of our internal optical people, and they sent me quite a lot of data showing that our lenses are dead on when it comes to exposure. Then they sent me data showing that non-Signature Prime lenses are accurate under some conditions, but not others. This is where I learned how T-stops are calibrated, and also a bit about how lenses are made.

The Not So Secret T-Stop Machine

T-stops and f/stops are different things. An f/stop is the focal length divided by the diameter of the aperture. For example:

50mm focal length / 25mm aperture diameter = 2

If “f” is the focal length, then the ratio of the focal length to the aperture diameter is f/2. Look familiar?

This is a mathematical formula that doesn’t take into account that light is scattered and lost as it passes though a lens. An untreated glass-to-air surface results in a light loss of 4-6% due to reflection or absorption, and an f/number doesn’t describe that loss. Lens coatings reduce this loss, but cannot eliminate it completely.

A T-stop is simply an f/stop number that compensates for this loss. A lens is placed on a machine that projects a known quantity of light through the lens. The lens is focused at infinity, and a sensor measures the amount of light that passes through the center of the lens. The amount that comes out the back of the lens is compared to the amount of light that enters the front, and the difference between the two determines the T-stop.

For example, a lens may pass a quarter to a third of a stop less light than its f/stop would indicate, and the T-stop takes this into account. A lens that is T2.8 might actually be f/2.6. (The f/number is always wider than the T-stop.) That way, when you use a light meter and set your lens to a certain T-stop, you’ll see an image with the proper exposure, even though the actual, mathematically-derived f/stop might be different.

Everyone uses the same T-stop machine. It’s made by Zeiss. If we’re all doing the same thing with the same machine, then the calibration process isn’t the answer.

It’s all about infinity

Lenses (excluding macros) are designed to work best at infinity. Everything else is a compromise. Hopefully not much of a compromise, but the closer one focuses any lens, the harder it is to make that lens look as good as it does at infinity.

One aspect of this is lens breathing. To focus a lens, optical elements move forward and back within the lens. Doing this changes the lens magnification, or size of the image projected onto the sensor. This zooming effect is known as “lens breathing.” It’s very common in still lenses, but it can be seen in a lot of cinema lenses as well. The best way to determine how much a lens breathes is to rack focus dramatically with the lens stopped down to around T11, as very soft backgrounds tend to conceal lens breathing. If the image changes size when you do this, then you’re seeing lens breathing.

The reason we’re talking about lens breathing is because this change in magnification results in a loss of exposure. As the image size increases, the light energy is spread across a larger surface, which means every point inside that image is now dimmer than it was when the lens was focused at infinity and the image was smaller.

The change of exposure that happens as a result of lens breathing is called “focus ramping.” As focus is moved forward, away from infinity, overall exposure drops.

There is a fix for this. As one group of elements moves to adjust focus, another group of elements can move a different way to counteract this change of magnification. This is a complex process, as the compensatory elements must move perfectly in relation to the focusing group, and any time one adds more glass to a lens the design, the complexity of the design increases.

ARRI Signature Primes are very well corrected for image breathing, and so far I’ve not detected any focus ramping on them at all—and this in spite of the fact that the 12mm and 280mm show minor focus breathing. (With extreme focal lengths, breathing is impossible to eliminate as one simply runs out of room to move the necessary elements the proper distance. Signature Primes breathe less than any other lens type I’ve tested, even at extreme focal lengths.)

Signature Primes aren’t necessarily brighter than other lenses. It may be that the other lenses, when focused forward from infinity, are darker.

The test

I don’t have access to a Zeiss T-stop calibration machine. I do have access to a matte box, a fresnel lamp, and a piece of typing paper. As I’m not calibrating a lens, but only observing its behavior, this is enough.

Here’s my methodology:

1. Put an ARRI Signature Prime on a camera (in this case, a Sony Venice, using a Wooden Camera LPL mount)
2. Cover the matte box with thick white typing paper
3. Light the typing paper from behind with a fresnel lamp to create a soft, diffuse, even light source
4. Set the lens’s T-stop to T4
5. Focus the lens to infinity and roll a second of footage
6. Set the lens to 6′ and roll a second of footage
7. Repeat at t2

Then I ran through the same procedure again with a competitor’s lens.

If focus ramping occurs in a lens, then I should see one exposure level when the lens is focused at infinity, and a different one when the lens is focused at 6′.

(I tested a 75mm ARRI Signature Prime. The competing brand didn’t offer a 75mm focal length so I used the next closest lens within 10mm.)

The Signature Prime shows some vignetting at wide open, which is normal. Eliminating this kind of shading at very wide f/stops requires the lens to be much bigger, and therefore heavier. Every manufacturer compromises in this way. This vignetting manifests in the form of cat’s eye bokeh.

And now, a competitor’s lens.

It appears focus ramping is real.

The curse

I’ve been thinking about why I might not have noticed this. It appears to affect lenses from 40mm up, so this effect wouldn’t show up in wide shots. It should show up more often in closeups, but if a person’s face is large enough in the frame then an image can be a little darker and we’ll still see plenty of detail. The difference in exposure might not register psychologically.

In the end, the drop in exposure is only about a half stop (at least for this particular lens, at this focal length, and at this focus distance; other lenses will differ) and this is easily fixed in post… if the exposure is beefy enough, and if the colorist knows to ramp exposure if the focus shifts from a distant subject to a much closer one. If you’re playing your exposures right on the edge, or working at a high ISO, or working with a director and/or producers who have mandated a “I want to see the actors faces clearly at all times” brightness level then this half stop could make a difference.

This can also skew your sense of exposure. For years, I was intensely frustrated by the fact that my light meters almost never agreed with what I saw on the monitor, and I’d always blamed the camera for this. Now I know that lenses played a role as well.

I was blissfully unaware of focus ramping for my entire career. Now that I know about it, I will never stop looking for it. And now I have passed that curse on to you. Enjoy.

Art Adams is Cinema Lens Specialist at ARRI, Inc. You can reach him here.

“Not my department, kid,” he said. “I just keep it in focus.”

I didn’t use much diffusion filtration when I shot film. Later in my career, when I found myself shooting lots of video, I was more willing to experiment. At that time, video cameras had a reputation for being too sharp, and a lot of cinematographers used rear nets to take the edge off the image. Front filtration required a matte box, and a lot of jobs either wouldn’t rent one or moved too fast to make using one worthwhile. Rear nets were easier to manage.

A San Francisco Bay Area cinematographer, Jim Iacona, saw an opportunity to both make his life easier and make a buck at the same time. He invented the I-Ring, which came in two parts: a base that slipped onto the back of a B4-mount broadcast zoom lens, and a ring that clipped onto it. To use it, you’d stretch a net over the base, clip it on with the ring, and then trim away the excess material.

I had at least four of these ready to go at any given time.

As HD took off, I spent less and less time with nets. The Sony F900 looked sharp out of the box but turning the detail enhancement down to about -40 (in what I call “Sony Arbitrary Units”) resulted in a pleasing look. (Turning the detail circuit completely off worked well for feature films but, strangely, resulted in an image that was too soft for broadcast.) The original Panasonic Varicam had a natural softness to its image that didn’t respond well to additional diffusion.

Until recently, I hadn’t tried nets on single sensor cameras, as the only ways to do this involved rubber cement or nail polish. As a DP, I shot mostly commercial and corporate projects. Neither of those methods was appropriate for use on a one-day project.

When I saw the rear magnetic holder on the back of an ARRI Signature Prime, I immediately flashed back to that cold night on a dark Hollywood street. I decided it was time to refresh my knowledge of how rear-mounted nets work.

THE CONTENDERS

I spent about a half hour at a fabric shop (Joann Fabrics, for those of you in the U.S.) before settling on the choices above.

My favorite net for B4-mount broadcast work was bobbinet, which is the material used in grip nets. The material at the far left, fine black tule, is a variant on this theme, but with a finer weave. The holes are hexagonal, and very round, so flares glow instead of radiating as star patterns. (Hard-edged holes in a net result in sharp, angular flares.) A lot of my broadcast video contemporaries used wedding veil, which has a very shiny, square weave, but this created four-pointed stars around even the softest highlights. That wasn’t my style.

Black sparkle mesh looked like fun. It was coarse enough and dense enough to work well as diffusion, but I didn’t know what its texture might impart to the image, or whether it would fall completely out of focus. It’s one thing for the pattern of the net to show up in soft highlights, but quite another for it to appear overlaid on a sharp subject.

Lastly, I chose silver sparkle mesh under the assumption that if black sparkle mesh turned out to be fun, silver sparkle mesh would be ten times as much fun.

Now that third-party LPL mounts are fairly widespread, I’ve been shooting a lot of tests with ARRI Signature Primes on non-ARRI cameras. Last week I had a Sony Venice in house, so while shooting another project I took the opportunity to conduct a quick net comparison test. With the camera set to EI 500 and X-OCN ST, I quickly set up and shot a net comparison.

Film is an abstract medium. It has a number of characteristics that digital doesn’t: grain, gate weave, layered color records, and an inability to view the results in real time. Because of these traits, dailies possess an element of surprise. The combination of texture and movement, even in a static image, and the fact that the exposure and color often looked better than we remembered when we captured the image, lent film a bit of a mystique.

Digital is often referred to as being too “clean,” and I’ve come to interpret this as meaning it lacks abstraction and mystery. Digital is predictable. There’s no gate weave, noise is not the same as grain, and you can (roughly) see what you’re getting while shooting. We generally know what we’re going to get, and some cinematographers don’t like that. They want, say, 10% of that process to be imperfect. They yearn for the “creative surprise.”

As an industry, I think we’re trying to recapture some of that mystery through the use of vintage glass. Flares, distortions, spherical aberration, and other optical anomalies capture some of that creative unpredictability that we enjoyed with film. This presents a quandary for ARRI, as we’ve always made lenses at the cutting edge of physics. Our lenses are beautiful, but they are intentionally beautiful. There aren’t a lot of random surprises.

Fortunately, the product manager for our optical products has a long history of classical lens admiration. For the Signature Primes, he opted to start with a perfect lens but then incorporate some classical lens features. Even though Signatue Primes are almost entirely free of distortion, spherical aberration, and chromatic aberration, Signature Primes are also slightly warm (to pop flesh tone), appear low in contrast (due to lack of focus ramping), are low in micro contrast (for smooth skin tone even at extremely high resolutions), and crafted to flare subtly rather than to completely avoid flaring at all. His intent was to create a beautiful and interesting look that is future-proof for ultra high definition and high dynamic range television, where optical imperfections are enhanced by a factor of 10 and can be incredibly distracting.

At the same time, he made it easy to introduce creative unpredictability into an otherwise near-perfect and already-beautiful image. The rear magnetic holder simplifies the attachment of nets and optical elements to the rear of the lens, making it easy to draw out the classic qualities of the lenses.

As you can see above, the base look is very attractive. Our model’s skin is smooth and beautiful. At the same time, the lens isn’t soft: fine detail is preserved, but it’s not accentuated or over-enhanced. Also, telecentric bokeh is very smooth, and backgrounds often feel as if one is looking through a rainy window.

Speaking of backgrounds, we’re looking at a bookcase and a coat rack draped with light bulbs. Remember the angle of the books. That will be important later.

Let’s look at some actual nets.

FINE BLACK TULE

One of the first nets I tried on the back of a Signature Prime was classic Christian Dior #5 pantyhose, used by film cinematographers for decades. At the time I felt it photographed too strongly, so I chose to test a variation of my old broadcast go-to, bobbinet.

Fine black tule has a definite smoothing quality. It reduces resolution and conceals skin imperfections while showing very little impact on the out-of-focus areas of the image. Anything placed very close to the front or rear of the lens tends to add texture to the out-of-focus portions of the image, so one should always choose diffusion materials and filters with these effects in mind. Soft backgrounds are the stage against which we set the action of a scene, and their quality is often as important as the subjects we photograph against them.

This is a subtle version of the Christian Dior #5 effect. It’s very flattering, but it is not a look one sees much anymore. You’ll see this look in a lot on feature film closeups from the 1940s, 1950s, and 1960s.

The net image is a little warmer than the image without the net. This is likely due to the net fabric spreading the warm light from the lightbulbs visible in the background.

I’m told that the pattern of the net appearing in out-of-focus highlights has something to do with the wave nature of light. This effect occurs whenever we shoot through a filter or fabric that has a pattern to it.

This blurry image shows books leaning on a shelf in the background. They aren’t important now, but after I change filters they will become very interesting indeed. Let’s do that now.

BLACK SPARKLE MESH

This show a subtler version of the fine black tule effect, but this net does some different things to the background. Let’s look at our model’s face first.

This net imparts a slight haze reminiscent of spherical aberration. It’s subtle, and I’m a huge fan of subtle. This is an effect that the audience will feel without consciously recognizing.

Once again, the netted image is warmer due to the shiny fabric catching and spreading the light from the bulbs in the background.

This next bit is the interesting part.

Notice how background textures look like brushstrokes? There’s a highlight at the bottom left that reveals the pattern of the mesh, but the out-of-focus bookshelves feel as if they’ve been painted in. The effect is even stronger on the other side of the frame.

My theory is that the holes in the fabric become virtual apertures that bring background textures into focus. I saw something similar a while back when comparing bokeh characteristics between wildly different types of lenses: ARRI Zeiss Master Primes and Cooke S4s.

Master Primes have fairly round irises, while Cooke S4 irises have an octagonal scalloped shape at wider T-stops. This has a fascinating effect on bokeh.

I see some structure to the out-of-focus wires that run between the lights, but it’s fairly soft.

I see the wire structure more clearly here. Wherever a wire lines up with one of the hard iris edges, it becomes sharper.

My suspicion is that black sparkle mesh subtly enhances background textures that line up with the coarse patterns within the net. This includes books, hair, shelves… anything that’s a hard line with some inherent contrast.

Let’s take a look at one more net.

SILVER SPARKLE MESH

This image is much warmer than the others, and I assume this is because the silver net material is doing the best job of spreading the warm light from the background across the frame. I see the same brushstroke patterns in the background that I saw in the black version of this same material.

The diffusion effect is quite strong. This is the lightest and shiniest fabric, so it’s throwing light everywhere.

Once again, the texture of the net enhances background textures that align with portions of its mesh.

What I love most about this fabric is the quality of the lens flares it creates.

If one finds just the right spot, one can create veiling glare that reveals the pattern of the net.

If one directs light into the lens, the effect is very different.

I originally noticed this effect while photographing this same model for the ARRI Mini LF launch event in Burbank. I happened to pan past a backlight with this particular net in place, and suddenly I felt as if I was underwater, staring up at rays of sunlight.

As I panned the camera left and right, the texture of the rays changed. It was absolutely fascinating. I’m afraid to say that I played around this this net for way too long. (At the time, I didn’t test this effect with the black sparkle mesh. I’ve since performed the same test, and it shows the same effect, only with much more subtlety.)

REAR NETS: NOT JUST FOR OLD FILMS ANYMORE

Rear nets have fallen out of favor over the last decade or two, but as cinematographers search for new ways to capture the unpredictability of film in digital imagery, old-school tricks like this may find new life.

In the 1990s, the same DP who invented the I-ring created another product called LightBreaks. They were clear, heat-resistant sheets printed with black patterns and textures, to take the place of the traditional wood cucaloris. The first time he showed them to me I shied away from the more recognizable patterns, such as thunderbolts, assuming they would be too hokey. “Trust me,” he said. “Give them a try.” Sure enough, the thunderbolt pattern looked great, and in practice the shadows it cast didn’t look much like thunderbolts at all. It became one of my go-to patterns. (Here’s an example from the old Lightbreaks website, circa 2003.)

To me, a fine repeating pattern is less interesting to me than the organic, semi-random, curvy weave of the sparkle mesh fabrics. The rear magnetic holder on the Signature Primes makes it dead easy to quickly cycle through a number of fabrics that may not look right by eye, but may produce amazing and unpredictable results when placed behind a lens. Sometimes the option that looks the strangest can yield the most interesting results. The only way to know is to try.

BUT WAIT, THERE’S MORE…

We’ve been experimenting with placing optical elements into our rear magnetic holders. It’s dead simple to take one of these holders to an optometrist and have custom diopters made. During a recent third-party test with a variety of different custom diopter elements, we found that we could match the looks of a number of vintage lenses with a consistency never seen before.

This will only become more interesting.

Art Adams is Cinema Lens Specialist at ARRI, Inc. You can reach him here.

Come see me on June 6th at Sim Video in Vancouver, B.C., where I’ll co-present a session on ARRI Signature Primes with product manager Thorsten Meywald. Francois Gauthier, technical sales rep for Canada, will give a presentation on the new ARRI Mini LF. And yes, we’ll have a prototype Mini LF on hand.

We’ll have two sessions, one in the afternoon and one in the evening. You can sign up here.

Art Adams is Cinema Lens Specialist with ARRI, Inc. You can reach him here.

Disclosure: after several decades as a director of photography, I now work for ARRI, Inc. as Cinema Lens Specialist.

Last week, I posted this article and asked you to take a look at four lenses in a direct comparison:

And now, the names:

Lens A is an 85mm Zeiss Supreme Prime.

The Supreme Prime is a classic example of a Zeiss lens. It’s contrasty and sharp, which emphasizes textures and resolution. Of the lenses in this test, this one emphasizes skin tone texture the most. It doesn’t show the deepest shadows (that award goes to C) but it’s close.

In the still world, a lens like this would be described as having “3D pop.” Many still photographers like to see a lot of high-frequency detail in their images as the texture makes them feel more “real.” Another description for this might be “high micro contrast.”

Micro contrast describes how quickly tiny structures in the image transition from bright to dark. It’s similar to photographic contrast, but refers specifically to fine detail such as clothing textures and skin. High micro contrast generally means such textures appear crisp and sharp, while low micro contrast means they appear soft and smooth. (“Micro contrast” is a poorly-defined term with no scientific basis, but it’s useful and we generally understand what it describes.)

Something to think about going forward: is this lens cool, or is it neutral in color?

Lens B is a 75mm Cooke S7.

This is, for me, the softest lens in the test. This is probably why it’s considered to be so flattering to actors: skin tone is very smooth. The shadows show a lot of detail, and it ties with lens D in this regard. Hair detail is not as crisp as on the Supreme.

What’s opening the shadows, though, appears to be flare. The fill side has a cool cast to it, which I think is flare from the mural in the background. I’ve seen this happen with other models of Cooke lenses (S4s and Speed Panchros) where soft sources at the edges of the frame can add a bit of veiling glare.

The Cooke reputation for being kind to actors appears to be related to how it handles high frequency detail and contrast. It could be described as having low micro contrast, as fine details aren’t rendered as crisply as in a Zeiss lens.

Lens C is a 70mm Leitz Thalia.

This lens appears to show a bit more micro contrast than the Cooke, but not so much as the Supreme. Skin texture falls somewhere between the two. When I look at her hair, once again the resolution falls somewhere between the Supreme and the Cooke.

This lens has the deepest shadows of all four lenses. In the other lens images, I can see her ear on the fill side. On this lens, I can’t.

The Thalia can also be said to have high micro contrast, although not as much as the Zeiss.

Lens D is a 75mm ARRI Signature Prime.

This shouldn’t be a surprise, as I shot this test to try to quantify where it falls in relation to the others. I have a lot more to say about this lens as I know it the best, and I’ve also learned quite a lot about lenses in general by trying to quantify its qualities. So… if I sound biased, I likely am. That’s why I posted the images above, in the largest files PVC would reasonably allow. You’re welcome to your own opinions.

This lens appears warm, and—until recently—that’s what I believed. I’ve long thought that Zeiss lenses were neutral in color and that Cooke lenses were warm, but a chat with people who know better than I disabused me of this notion. According to them, Zeiss and Cooke lenses are actually on the cool side, while Signature Primes have the tiniest degree of warmth.

I think this is apparent in the images above. A, B, and C are all cooler by comparison. The Signature Prime is either objectively warmer (by design) or subjectively warmer (by comparison). Based on my observations, the Supreme seems to be the coolest. The Thalia is cool but less so than the Supreme. The Cooke is the closest to neutral, but still a touch on the cool side. The Signature Prime is either neutral or slightly warm. The best place to look for this coolness is in our model’s lips, which the Signature Primes render as a warm red, but the other lenses show as a cooler, duller red.

In a separate test, I shot color charts with an ARRI/Zeiss Master Prime, a Cooke S7, a Leitz Thalia, and an ARRI Signature Prime. At 3200K preset on an ARRI camera, I saw that the other lenses were slightly blue or cyan, and the Signature Prime showed a hint of yellow. This may be why the skin tone seems to pop so nicely.

The other reason skin tone pops is because Signature Primes appear brighter than the other lenses by about 1/3-1/2 stop. This is consistent across the entire lens line. In my tests I’ve seen other lens types that are consistently dark by comparison, so there does seem to be some variability in how lenses are calibrated. I don’t yet have an explanation for this, but we generally do things right (ARRI is a hard-core engineering company) so I’ll be curious to see how our methodology differs from that of other manufacturers. I do know we use the same calibration machines that everyone else does.

The Signature Prime shadows look to be as open as the Cooke S7, but I don’t see any obvious flare. I certainly don’t see the same blue-tinted veiling glare on the fill side. I’d say this lens can be described as having moderate micro contrast: it captures very high resolution images, but renders that detail in a very natural way that’s not sharp or soft.

In general, my overall impressions are:

The ARRI Signature Prime is the warmest, or the least blue, depending on your perspective. The Cooke S7 is second up in the warmth category. The Leitz Thalia is cooler, and the Zeiss Supreme is coolest.

The Leitz Thalia and Zeiss Supreme Prime show the least shadow detail. The ARRI Signature Prime and the Cooke S7 show the most shadow detail, although in the case of the Cooke this may be due to flare.

The Cooke S7 is the softest lens of this group. The Zeiss Supreme appears to be sharpest, likely due to contrast. Her hair doesn’t seem as finely resolved as I see in the ARRI Signature Prime, but the lens feels sharper, and that’s likely due to higher micro contrast.

The Leitz and ARRI lenses are close in sharpness, but when I look at the model’s hair the Signature Prime seems to resolve more detail. At the same time, it renders skin more smoothly, which I think is due to its lower micro contrast. The Leitz seems sharper because it renders shadows and dark tones the darkest of any of the lenses tested, but it doesn’t appear to resolve hair detail as well as the Signature Prime. The Signature Prime captures more detail, but it feels less sharp because it renders that detail without strong micro contrast.

This comparison was certainly a bit of a surprise. I hope you found it as informative as I have.

Art Adams is Cinema Lens Specialist at ARRI, Inc. He can be reached here.

I do a fair amount of this in my new job (Cinema Lens Specialist at ARRI, Inc.), as I did in my old job (freelance cinematographer for 26 years). Such tests are difficult to do well, but I’ve gotten reasonably good at it over the years.

What I’m posting here is one of my more recent comparisons.

That’s right, I’m not posting names. Not yet. Those will come next week. Right now I’m going to tell you how we shot this test, post some full-size images, and suggest what to look at.

• All images were shot on an ARRI camera.
• I did no grading other than to apply the default ARRI 709 LUT in Resolve.
• Images were exported as TIFF files, and converted to PNG files to retain as much fine detail as possible. (The original TIFF files are 50 megs each, and PVC only allows JPEG, PNG and GIF image files, so while conversion was necessary, I chose the format that was the least destructive.) Note: BlackMagic Resolve appears to render JPEGs with a lot more contrast than TIFFs, which is why I chose to export TIFF files and convert them to PNGs. The TIFFs are considerably lower in contrast.
• The distance to the subject didn’t change. When possible, I used matching focal lengths. In two cases this wasn’t possible, so we chose the next nearest focal length.
• All lens apertures were set to T4. I wanted to close down enough that we’d be working close to the sweet spot of each lens. An old rule of thumb stated that the sweet spot for lens sharpness and contrast could be found 2 2/3 stops closed from wide open. Modern lenses clean up a lot faster, but I didn’t want to shoot wide open as even the best lenses show some oddities that go away quickly when stopped down. I wanted each lens to look the best it could.
• Our model was keyed with a 1K open-face tungsten light through stacked 4’x4′ frames of poly silk and Lee 216. A hint of fill came from a nearby 4’x4′ bounce card. Backlight came from a Quasar tube over the set wall, and the mural in the background was top-lit by a tungsten fresnel. I chose tungsten light because it’s a common light source that we all understand. If I’d gone with an LED light then the results would only be valid for that particular combination of LED brand and model. Also, as tungsten is a broad-spectrum light source, the results should be the best possible, particularly for skin tone.

Below are full-size images. I encourage you to zoom in and look around. In particular, look at:

• Skin tone color
• Skin texture
• Exposure
• Hair
• Exposure (key side)
• Contrast (fill side)
• Flare (fill side)

Extra credit:

• Overall color
• Background color
• Bokeh (keeping in mind that bokeh refers not just to highlights but to the overall quality of the out of focus image, and that two of the lenses are slightly different focal lengths compared to the two others)

Check back Wednesday for the results, along my own thoughts.

Thanks to director of photography Matt Siegel for his help in shooting these tests.

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

I’ve heard a lot of theories as to why large format looks different from traditional S35. As best I can tell, it boils down to reduced depth of field. To match the angle of view between a large format camera and an S35 camera, the large format camera will require a longer lens, and this results in an apparent reduction of depth of field. In the case of an ARRI Mini vs. an ARRI Alexa LF or Mini LF, depth of field can shrink by up to 50%.

But is it really this simple?

THE DISTORTION ARGUMENT

It’s easier to correct long focal length lenses for optical distortion. The fact that large format cameras require longer lenses than S35 cameras to capture wide angles of view suggests that wide shots will show less distortion, which may make them feel more “immersive.” I don’t know that this is the case with modern cinema lenses as they tend to be very well corrected for distortion.

I compared two sets of well-corrected cinema lenses: ARRI Master Primes and ARRI Signature Primes. Master Primes are nearly optically perfect cinema lenses, while Signature Primes possess a unique combination of modern and classic attributes. Distortion, though, is not one of those classic attributes.

Master Primes cover S35 but not large format. Signature Primes are designed for both formats. Let’s see how they compare.

I blackmailed Technical Sales Rep Chase Hagen into posing for me. We captured two passes on an ARRI Alexa LF: one with a Master Prime in 3.2K, and one with a Signature Prime in 4.5K. The camera remained static between the two passes. (I chose 3.2K because it’s the format I used most toward the end of my stint as a freelance cinematographer.)

I see no difference in distortion here. What I do notice is that the Signature Prime is warmer than the Master Prime and reproduces the background with more vibrancy and contrast, even though it’s softer. The Signature Prime shows a bit more vignetting than the Master Prime, but that’s because its aperture is wide open, where the Master Prime’s aperture is not.

I see no differences between these images beyond each lens’s unique characteristics and large format’s reduced depth of field

If you’d like to know the (very simple) math used to calculate the crop factor between 3.2K and 4.5K, scroll to the end of the article. It’s really useful stuff but might not be interesting to everyone. The key takeaway is that it’s dead easy to determine what lens to use for the equivalent angle of view between 3.2K on a Mini and 4.5k on an Alexa LF (or between 2.8K HD and UHD): just move up to the next standard focal length.

25mm (Mini) > LF 35mm (LF or Mini)

35mm (Mini) > 50mm (LF or Mini)

50mm (Mini) > 75mm (LF or Mini)

75mm (Mini) > 100mm (LF or Mini)

Each step results in a reduction in depth of field by half.

DEPTH OF FIELD, PERSPECTIVE, AND DEPTH

The most obvious difference between large format and S35 is the reduction in depth of field. Large format may offer a clear advantage to those who like to shoot soft backgrounds.

In my own work, I’ve found that reduced depth of field in S35 becomes interesting at T2. Most of my freelance work was in commercials, and I found that T2.8 often felt a bit too sharp for modern tastes. In large format, though, that was often the equivalent of shooting T2 in S35.

Shooting wider than T2 can be… problematic. T1.4 on a fast lens is really f/1.2 or f/1.3, and at that point, spherical aberration is difficult to correct. This can cause apparent shifts in focus at wide apertures. This is also known as “witness mark drift.”

I saw an example of this early in my career when a lens manufacturer released a series of lenses that were frighteningly honest about this anomaly: they sported a yellow witness mark for apertures smaller than T2.8, and a blue witness mark for apertures wider than T2.8. (Shooting at T2.4 was a bit nervewracking.) They knew that, when the lens was wider than T2.8, the lens looked sharper if the lens focused at a slightly different point.

Many cinematographers who habitually work wide open have their lenses shimmed to compensate for this. In the large format world, there’s no need to work at T1.4 to capture the same look.

Or, one can work at that aperture and capture backgrounds that are far softer than what one can create in S35. I’ve seen images, captured with our own ARRI Signature Primes at T1.8, that look as if there’s a water-covered window between the subject and the background. It’s a wonderfully dreamy look.

How much of an effect does reduced depth of field have on the “large format look,” though? I worked with director of photography Matt Siegel to find out.

I imagined that we were shooting in a small room, with no space to maneuver. We then crafted and captured a series of shots from the same camera position, and with the same angle of view and T-stop, but in both 3.2K and 4.5K Open Gate modes on an ARRI Alexa LF.

Before you watch the video below, I’m going to tell you what I want you to look for:

The shapes of background objects grow as they drift out of focus. This may make soft backgrounds feel closer, while also creating a greater sense of separation between foreground and background due to their increased softness.

Wide shots may feel deeper because they show increased perspective without hard edges that compete with the foreground. They feel “flatter” while retaining a sense of depth as if the image is composed of discrete layers. (I equate this to the sense of depth I’ve felt when viewing wide shots in 70mm films.) It’s almost as if the foreground is a cut-out, placed against a soft background.

As I illustrated in this article, anamorphic and spherical lenses of the same focal length will show the same depth of field for the same active sensor size, but the spherical lens will render backgrounds as softer.

For example, when shooting anamorphic with an ARRI Alexa LF, we use UHD mode. We can also shoot in this mode with a spherical lens. The image heights on the sensor are the same. The spherical lens is the same focal length in both axes, but the horizontal axis of the anamorphic lens is half that of the vertical axis. Objects will soften normally in the vertical dimension, but they’ll stay sharper longer in the horizontal dimension.

Under these conditions, a spherical lens will produce softer backgrounds because focus drops off equally in both dimensions.

There’s an example of this at the end of the video. I digitally zoomed in to the pictures in the background to show that the spherical lens softens the horizontal and vertical frame edges equally, but the anamorphic lens doesn’t soften the vertical edges nearly as much. I wasn’t able to perfectly match focal lengths due to lens availability so I had to scale the 75mm spherical lens up a bit, but I think you’ll see what I’m talking about.

The large format background feels larger in relation to the foreground when compared to the 3.2K image. There’s also a noticeable exposure drop in the background highlights as they bleed into the surrounding dark areas. This might be considered a bonus—particularly in HDR—as highlights remain visible but are less distracting.

Part of the sense of depth I feel in the large format image has to do with the increased size of the out-of-focus pictures on the background wall. Another aspect is that hard edges in the background are so much softer in large format that my brain can’t “grab on” to them. It feels as if the woman in the foreground is on her own “depth layer” that’s distinctly separate from the other layers.

The woman feels to me as if she is part of a foreground depth layer that contains the foreground bookcase. The man feels as if he’s on another depth layer that contains the camera-left bookcase. And the background wall feels as if it’s a third depth layer. I still feel this someone in the S35 image, but it’s undeniably obvious to me in the LF image.

I quite like what’s happening in the large format frame. The perspective of the room feels “flatter” somehow, but I perceive the layers of depth more strongly.

What’s interesting to me is that I feel less of that “layered depth” sensation in the 2.39:1 images. I’ve noticed this before when shooting location stills with a 1.5:1 digital camera vs. shooting moving images in 16:9: taller images often feel as if they have a greater sense of depth. As best I can tell, this is strictly a function of psychology, and is heavily dependent on the size of the image. Here, anamorphic images don’t feel as rich in depth as do the 16:9 images above. If they were projected on a huge screen, though, I suspect I’d feel plenty of depth.

There are two additional things I’ll touch on before I wrap up. The first is that DP Matt Siegel and I both agree that we feel that large format 2.39:1 to one feels more immersive to us. I think this is due to the way spherical lenses drift out of focus, although he was blown away when I showed him these two videos (originally seen in this article):

In both cases, he said he felt that the image “wrapped around” him and created a sense of immersion. As mentioned above, wide images seem to have less depth when viewed on a small screen, but Matt saw these projected on a large screen in the theater at our new Burbank office. It’s safe to say that he was… “verbally expressive” when these videos came up.

My humble guess is that the lack of background distortion in the spherical lens’s image created a strong sense of immersion that was tempered by the anamorphic lens’s distorted and slightly sharper bokeh.

Lastly, there’s a strong case to be made for large format’s increased sense of depth when shooting for very small screens.

Softer backgrounds create a greater sense of depth on small screens. I’d love to be a film snob, but I watch an awful lot of television on my iPad during long plane flights, and television cinematography currently rivals anything I see in feature films. While an iPad is not an ideal viewing platform for cinematography, I can’t turn that part of my brain off just because I’m watching content on a small screen. And neither, I suspect, can you.

Art Adams freelanced in the film industry for 31 years and was a cinematographer for 26 of them. He is now Cinema Lens Specialist at ARRI, Inc. He’ll be at NAB 2019 in the ARRI booth, so stop by and say hi.

AND NOW, SOME SIMPLE MATH

To match the angles of view between 3.2K and 4.5K, I had to use a longer lens in 4.5K. The question was, “How much longer?” Upon consulting PCam, I found that the angle of view of a 35mm lens in 4.5K matched a 25mm lens in 3.2K. This is a “crop factor” of roughly 1.4x. This has an interesting property:

25mm * 1.4 “crop factor” = 35mm

I took this a bit further to see if it applied across a standard range of lenses. It does:

18mm * 1.4 = 25.2 (or ~25mm)

25mm * 1.4 = 35mm

35mm * 1.4 = 49mm (or ~50mm)

50mm * 1.4 = 70mm

70mm * 1.4 = 98mm (or ~100mm)

If we consider a standard set of primes to be 18, 25, 35, 50, 75, and 100, then converting from 3.2K to 4.5K simply means bumping up to the next longer focal length in the set. This also holds roughly true when converting from ARRI HD to UHD (1.33 vs. 1.4, which is a bit different but close enough to make focal length conversions easy).

This also works for slightly different focal lengths such as 16mm and 24mm, although it doesn’t work quite as well for less common (but really useful) focal lengths such as 40mm and 65mm.

One can easily determine the “crop factor” for any two sensors through some basic division. Divide the horizontal pixel count of the large sensor camera by the horizontal pixel count of the small sensor camera, and that’s your multiplier. If the cameras are configured to capture images with the same aspect ratio, multiply the smaller camera’s focal length by the multiplier to find a focal length that will give the same angle of view on the larger camera.

For example:

ARRI Mini, 3.2K mode: 3200px wide

ARRI Alexa LF, 4.5K open gate: 4448px wide

Multiplier = 4448px / 3200px = 1.39 (or round off to 1.4)

If I have a 25mm lens on an ARRI Mini in 3.2K, I’ll need a 35mm lens on an ARRI Mini LF to capture the same angle of view (25mm * 1.4 = 35mm).

It’s important to note that this doesn’t work across images with different aspect ratios, as you can only calculate angle-of-view matches for horizontal or vertical angles. Using a diagonal to match, say, 16:9 to 2.39:1, won’t yield meaningful results.

As a camera assistant in the bygone days of film, I spent many nervous hours attaching nets to the backs of lenses using nail polish and/or rubber bands. I took things further when I began shooting video. Most of these jobs lasted only a day, so attaching a net to the back of a lens wasn’t feasible. After some experimentation, I settled on plastic cut from transparency film slide holders. I had no need to attach anything to the lens; instead, I sandwiched a circular piece of plastic between the lens and the sensor cover glass.

From there I experimented with color, which lead to my destroying a number of gel swatch books. (Chocolate was my favorite color as it made people look tan and fit. Shooting at the beach proved problematic, though, as blue water turned to mud.)

At that time, video cameras didn’t have menus. Adjusting aspects of the electronic image, such as manipulating the detail circuit (which drew a dark line around areas of high contrast to make edges look sharper) or tweaking the color matrix (which governed the color response of the camera), meant pulling the side off the camera and adjusting pots with a very small screwdriver. Most of us didn’t know enough to do this well, or at all. Cutting gel circles out of free swatch books was a lot easier.

Often a DP chose their favorite rental house based on the aesthetic preferences of the in-house engineer, who created a standard “shop look.” The few adjustments we made in the field were often brute force measures that made use of scissors over screwdrivers.

NTSC was a soft medium by today’s standards, and conventional wisdom dictated that audiences preferred sharp images. Hybrid directors of photography, who worked in both film and video, had a different point of view. I preferred softer images to artificially-sharpened ones.

Diffusion filtration was a lifesaver, but not always practical. As I transitioned from shooting film to video (having moved away from Hollywood to a smaller market, where video was dominant) I learned to do more with less. I rarely had a matte box, and often the only filter I carried was a polarizer, mounted in a clip-on sunshade. This made adding a 1/4 black Pro Mist (my old video standby) nearly impossible.

I wasn’t the only person with this problem. A San Francisco Bay Area-based DP, Jim Iacona, felt the same pain. His solution was to design and manufacture a behind-the-lens plastic net holder for B4-mount lenses. He called it the I-Ring. It consisted of two interlocking plastic rings. One stretched a piece of netting over the bottom ring and then snapped the top ring into place, capturing the fabric between the two rings. After trimming away the excess, it was dead simple to snap this assembly onto the back of a B4 zoom lens.

I owned three or four I-Rings, each made up with a different type of netting. My favorite material was bobbinet, which is the active ingredient in single and double grip nets. It has a hexagonal weave, so the holes in the netting appear smooth and round. Light spreads at a 90º angle to the thread, so the relatively round hole resulted in a soft glow instead of a star or cross effect. Many of my contemporaries used wedding veil, but the shiny cross-hatched weave turned every light source into a four-pointed star—even large, soft overhead fluorescents.

Fogal stocking material, long popular for use on the back of 35mm motion picture lenses, proved too thick for video use. This was unfortunate, as I knew several DPs who took “Fogal purchasing trips” to Paris every year and wrote them off their taxes.

Behind-the-lens nets provided a number of advantages over traditional glass filters. I didn’t need a matte box, which saved time and money. Front-of-lens diffusion had to be changed with the focal length to maintain a consistent look, but a behind-the-lens net created the same look at just about every focal length. And the net created interesting patterns in out-of-focus highlights.

The RED One camera changed everything. The Sony F900, a frequent recipient of behind-the-lens filtration and one of the last B4-mount cameras, faded into obscurity. Matte boxes became commonplace. We still used diffusion to create an analog feel in a digital medium, but at much lighter densities. Then the original ARRI Alexa changed everything again, as it didn’t have the same electronic feel that we saw in other digital cameras. Diffusion returned to its rightful place as a creative choice, rather than as a defensive weapon in the face of an immature technology.

Now it seems we’re in the midst of a visual renaissance. Digital cameras look better than ever, and I see a level of experimentation that I’ve never seen before. From episodic TV to independent films, filmmakers are exploring with looks more than I’ve ever seen. Behind-the-lens nets are making a comeback.

Last year, while teaching classes for The ARRI Academy, I was happily surprised to see the return of my old friend, the clip-on behind-the-lens net holder.

Every ARRI Signature Prime ships with a magnetic behind-the-lens magnetic filter holder. I won’t call it a net holder, as some enterprising cinematographers in Germany recently shot a demo that employed a wide variety of materials that extended well beyond netting. If you can fit something into that holder, and it is in some way transparent, you can make it into a filter.

There are a couple of phenomena that need to be clarified.

Streaks derive from highlights in diffusion material and run at 90º to the orientation of the material. We can see this more clearly in the bokeh of the next shot:

When dealing with an effect this strong, it’s important to control the direction of the streaks. They become a compositional element and can be used to direct attention and create tension within the frame. The I-Ring made this both simple and difficult, as the ring rotated freely, but it was difficult to gauge when an effect was perfectly vertical or horizontal. The Signature Prime filter holder is equipped with a witness mark and the magnets that hold the filter holder onto the lens act as click stops, so it’s dead simple to orient a net in a particular direction and duplicate that orientation across a number of lenses.

Putting a star-shaped aperture in the magnetic filter holder creates this image:

My crude understanding of this effect is this: the star-shaped aperture imposes its shape on the wavefronts of the out-of-focus highlights in semi-predictable ways. For example, in the image above, there’s a really sharp star on the left side of the frame that corresponds with an extremely soft highlight in the clean image above. The lights that are farther away, and less out-of-focus, are smaller and less distinct.

Also, as the star aperture is small, the effective f/number of the lens is reduced, increasing apparent depth-of-field. Note the power cables that are visible in the image above that are invisible in the clean image above it.

I’m not used to seeing such a strong, random texture in out-of-focus highlights. Normally we soften backgrounds to make them less distracting, but this filtration adds frenetic energy to the image. The hard texture causes my eye to move around the frame, but the swirling bokeh brings me back to the talent’s face.

This is really disturbing. I love it. There are so many creative uses for this.

This is a piece of aluminum foil, with lots of holes in it, placed behind the lens. Each hole becomes an aperture. When the subject is thrown out of focus, all the pinhole images diverge and create a cluster of hard-edged overlapping images. Years ago I did something similar with an F55 and a piece of foil, but the foil was placed in place of a lens, not behind it. I like this more.

I’ve long wondered why no one had reinvented the I-Ring for film use. Now it seems ARRI has done exactly this. It only makes sense. At the pace that modern crews have to work, no one has time to sit around and wait for nail polish to dry. And this net holder smells a lot better.

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.

I think this is the perfect time to share an image crafted by Adam Wilt, who sent it to me upon learning of my new job at ARRI. Those of you who are familiar with the 1960s counter-culture TV series “The Prisoner” may appreciate it.

These completely out-of-context snippets from the series will do nothing to help you understand this meme. Enjoy.

Recently, while shooting some lens tests at a rental house, I happened to notice something out of the corner of my eye. My Alexa LF was parked in a prep bay next to a Sony Venice, and when I panned past it I noticed the quality of the Sony logo varied with the lens I was using. I’ve learned better than to ignore such things, so I took a closer look.

At the time I noticed this oddity, I had a Leica Summicron-C on the camera. I rolled a few frames, swapped out the Leica lens for an ARRI Signature Prime, and rolled a few more frames. The following images were pulled from Blackmagic DaVinci Resolve in HD resolution.

The are two things to see here. The first is that the Sony logo looks crisper on the Summicron than on the Signature Prime. The second is that the Signature Prime renders the gray Venice exterior as slightly warmer and brighter. I’ve already addressed the fact that Signature Primes possess a golden hue and boost mid-tones while preserving deep blacks (see articles here and here), but I wasn’t completely sure why the Leica lens looked sharper than the Signature Prime.

It turns out that the reason is chromatic aberration.

There’s a more dramatic example at the right side of the frame.

Old broadcast cameras had a “detail circuit” that drew a thin black line around areas of high contrast to make the transition appear sharper, increasing the image’s apparent sharpness. Indeed, all modern cameras employ this type of enhancement—although the level of enhancement is often much less than I saw in the standard definition era and the early years of HD. Even ARRI cameras add a tiny bit of detail enhancement, but only when recording to ProRes.

The chromatic aberration in the Summicron lens serves this same purpose. The purple fringe outlines the letters in the Sony name, making them appear sharper than they are. They almost appear embossed.

I’ve noticed that Signature Primes don’t feel sharp or soft, both of which are deviations from normal. (We only think in terms of sharp or soft if something appears different from how we expect it to appear in reality.) Signature Primes simply feel real, as if I’m looking through a clear glass window instead of a lens. Their lack of chromatic aberration and distortion mean they simply get out of the way.

These lenses were recently reviewed by Alfonso Parra, a Colombia-based DP who excels at camera and lens tests, and in his final report, he describes Signature Primes as “immersive.” I feel exactly the same thing, and in fact, that’s what caught my attention in the images above. The Leica looked much as I expected a film lens to look: sharp. The Signature Prime looked… real. I’m not used to seeing that in images. It shouldn’t be a big deal, but then HDR shouldn’t be a big deal either. It’s simply the way we see the world. But when we see it on a screen… wow.

I’ve not learned yet exactly why Signature Primes feel this way, but I suspect it has something to do with telecentricity. Signature Primes are engineered such that light rays exit the lens at as close to a right angle to the sensor as possible. Photo sites have depth, and light rays that strike them at an angle may not penetrate fully, resulting in vignetting. They are also covered by microlenses, which can create color fringing effects when struck at shallow angles. Large format PL-mount lenses must work harder to cover a large sensor as the rear of the lens is smaller than the sensor. That’s why the LPL mount has a much larger diameter: in order to evenly illuminate the sensor with telecentric rays, the rear of the lens must be at least as large as the sensor itself.

In this article, I compared the bokeh of several different types of lenses and discovered that telecentricity results in very soft and smooth bokeh. It appears telecentricity has much the same effect at the point of focus.

Another interesting feature is that the Signature Prime rolls out of focus more gently than does the Leica. The “T” in “Tally” and the “P” in “Power” look harder in the Summicron image, while the Signature Prime renders them with a softer blur that almost feels as if it is superimposed.

There’s another area of the image that’s informative: the lens mount.

Chromatic aberration tends to be strongest at the edges of the frame, especially when a lens is wide open—as both of these are. (The Leica was set to T2, while the Signature Prime was set to T1.8. I balanced both lenses by using the gain control in Resolve to match the brightness levels of the white wall in the background.)

The Signature Prime shows some chromatic aberration, but it feels softer and bluer than the Summicron, which feels harder and is magenta in hue. Chromatic aberration is typically green or magenta, depending on whether it falls in front or in back of the point of focus. What little chromatic aberration is visible in the Signature Prime is either golden yellow or blue. These are “natural” colors, as we tend to see golden and blue light in nature. We almost never see green and magenta light in nature.

All of these variables factor into visual storytelling. Lenses can feel hard even if they aren’t sharp. They can resolve high-resolution detail and yet feel smooth. Sometimes it’s enough to feel the differences, but other times we must understand why these differences occur so that we can control and choose them. If I want to tell a story with a “hard” lens, do I want it to feel that way due to color fringing, or high micro contrast, or both? If I want a “soft” lens, do I want a lens that also resolves fine detail or glosses over it? Do I want a lens that distances the audience from the emotion of a scene, or that immerses them in it? Does the color of the aberration help or hurt? All of these are choices for the modern cinematographer. All of these give a lens “character” or “personality.”

Telecentricity clearly has its benefits, and the design of the LPL mount makes telecentric large format lenses possible. Wooden Camera recently announced LPL mounts for the Sony Venice, RED DSMC2, and Sony E-mount cameras, so here’s hoping that large format telecentricity is coming to a camera near you.

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.