What really makes a true cinema lens?

It takes more than just .8 pitch gears and repeatable focus to make a true “Cinema” lens, we look at the Arri Signature Primes and how they deal with the most cinematic element: time.

The bare minimum you need for a lens to be workable as a lens for motion pictures is a very low bar to cross.  Repeatable focus and .8 pitch gears for attaching a follow focus and you can call it a “cinema” lens. But as you think about what makes a lens truly “cinematic,” (not in the “scorsese vs. marvel, cinema vs. movies” sense but in the “aspiring to be the best something can be” sense), you start to look at all the other factors that go into crafting an image in time.

That’s the theme that keeps coming up over and over as you spend time with the Arri Signature primes: time.  Change over time. These are lenses that are truly not just designed to capture a single individual moment in time, but are truly intended to capture something that is changing, moving, dynamic in time.  Thus when Arri allowed us to spend a few hours shooting tests with the Signature Primes (and arranged a very informative call with in-house Cinematographer Art Adams), that was the element we wanted to focus on the most.

What does it mean to design a lens to capture images over time?  It means paying attention to how changes in focus and exposure affect the image.  After all, these are the first lenses that have only Arri’s name on them (unlike the Zeiss/Arri collaborations like the Master Primes or the Arri/Fujinon collaborations on Zooms).  They don’t make the lenses (an unnamed Japanese optical house that also makes high-end microscope and telescope optics does the manufacturing), but they specified the design parameters the manufacturer should target with a clear focus on motion and motion alone.  Unlike Zeiss and Fujinon which also make still photo equipment, Arri does one thing and one thing only, motion pictures.

Thus, as a motion picture house (though I bet an Arri stills camera would sell like hotcakes, right now they don’t make one), it makes sense that they would design lenses that in every way are focused on one thing.  How your shots change over time is built into every aspect of these lenses.

Focus Ramping

Well, first off it’s an unfortunate open secret in the world of lens design that most lenses change exposure as they change focus.  Lens manufacturers generally only calibrate their lenses when they are focused at infinity. When you rack focus through a shot, not only is the focal area changing (which you want), but also the exposure.  Sure, you could probably compensate if you really wanted, but you would likely over-correct if you tried. This effect is called focus ramping, and it’s super frustrating when trying to truly nail exposure and can lead to more time being spent in the final color grade matching shots at different focus distances.  For instance if the first half of the scene was shot with a character far away, then the second half they walk into the close-up.  A colorist under time pressure might be tempted to just copy the grade from the first half to the second half of the scene, without really appreciating just how much exposure changes as you ramp the focus closer to the lens.

Credit: Image Courtesy Arri

Thus with the Signature Primes Arri focused on evaluating exposure for every single part of the focus range.  Focus at infinity passes the precise same amount of light through the lens as focus at 4”. The results are most noticeable when shooting a grey card, but they are clearly there when you look for them whatever shot is happening in front of the lens.

Bokeh

Beyond simply looking just at how exposure changed with focus, Arri also put work into ensuring that the bokeh was properly corrected throughout the focus range. This means that as a character moves around in your shot, and elements move from focus to out of focus, they do so smoothly, with beautiful transitions that then lead to an out of focus area that feels organic and natural without being distracting.  The "donut bokeh" you sometimes see in lenses, where the outside of the bokeh ring in brighter than the inside, ends up leading to a "harder" feeling out of focus area, whereas with the Signature glass you see a much more smooth, slightly textured out of focus area.

In this image you see not only the round "bokeh balls" from the out of focus christmas lights, but also the smooth feeling to the out of focus chair and table.

In the words of Art Adams, "Signature Primes are very well corrected for spherical aberration, which means the bokeh is super soft and smooth even in Super 35. This gives the impression of greater depth separation, and makes backgrounds less distracting even at deep stops because hard edges just melt away. Everything about the bokeh is designed to gently direct attention back to the subject."

In the video below you can see an extreme focus rack (from close focus to the empire state building a borough away), watch as the image goes into and out of focus. You will also notice how little the framing changes throughout (basically not at all), which leads us to breathing.

Breathing

Breathing is that subtle reframing at the edges of a scene when you ramp through focus. On some lenses it's more dramatic than others, and in fact with many still lenses it's quite dramatic since a still lens only captures a single moment in time, so there is no need to design away breathing.  The Signature primes breathe very, very little; if there is any breathing at all, it's barely noticeable.  While some breathing is sometimes appealing to some filmmakers since it can feel "organic," it's often inconsistent from lens to lens in a series with vintage lens sets, and having consistent minimal breathing throughout the range is a major bonus.

Rolloff

Rolloff refers to the way in which a lens transitions from being in focus through out of focus.  In the image above, shot at an angle towards a focus chart, you can see how the Signature primes transition out of focus quite quickly (competitor lenses are "in focus" for a wider area), but also softly.  The difference between "in focus" and "out of focus" isn't as dramatic.  You can also see how with some vintage lenses aberration appears, especially on the magenta/green axis, as a lens leaves full focus and heads to out of focus.  By working to keep the transition between in focus and out of focus clean of aberration Arri has focused on a lens that looks pleasing all the way through the focus rack.

Flares

Arri has made a very bold swing against trend with these lenses, in that they have focused specifically controlling the color artifacts in flares.  This of course was a goal in lens design for a long time (before the 60s allowing a flare in your image was considered a mistake, and until the 90s it was rare to design a lens purposely for flares), and only recently have many lens designers been promoting their extensively flaring characteristics with deliberate color casts, but Arri have decided to focus on minimal flares with minimal color artifacts.  Flares are there, but they don't call attention to themselves.

Why?  HDR. We are rapidly moving towards all content being delivered in high dynamic range (most footage is already captured in high dynamic range: it’s really a factor in how much of that is preserved that matters).  However, most filmmakers still monitor on set in standard dynamic range.  That same flare that might look beautiful on your standard dynamic range monitor on set might look terrible in high dynamic range, with saturated unwanted colors appearing that were clipped out to pure white on set.

Day Exterior Sun Flare

As Arri believes universal HDR delivery will happen soon (and Netflix clearly agrees), they decided to focus these lenses on delivering what they felt to be the best possible experience in HDR, which means less color in the flares (that you might miss in SDR monitoring), and also more localized flares that don't spread over the whole frame.  

Rear Element Filter Ring

To balance that out, they have included a magnetic rear element filter ring for attached rear nets and silks that can create the kind of “personality” and flaring that filmmakers are often looking for.  This feature allows filmmakers to get the best of both worlds, lenses that have the option of absolutely no flare, but then also have the option of flaring like crazy if that fits the mood or project.

Credit: Image Courtesy Arri

Video is no longer available: vimeo.com/charleshaine/review/378509899/6a69191e3c

One interesting possibility here is rear-element diopters.  While there isn't yet an "Arri Signature Macro" and there have been no suggestions that their might be (no matter how much we might want one), the ability to mount a rear element diopter could potentially open up some possibilities for closer focus on some of the longer lenses.  If nothing else it's good to remember that you aren't limited just to nets but have a whole host of options for what you can stick behind the lens, and diopters have already been tested for creative "vintage" feeling filter effects.

The only change here is adding a rear black net to the lens. You can see not only a dramatic effect in the "bokeh balls," but also a difference in exposure and skintone reproduction. We suspect that since the signature primes are so "clean," we're likely to see a variety of rear element experimentation.

A True Digital Lens

Arri wanted to focus on making this a true digital lens.  Since it’s only available in LPL mount (the new mount that Arri will be using for all cameras going forward, even Super35mm bodies), and there are no LPL film cameras since there is a mirror in the way, Arri was free to focus on making this the ideal lens just for mirrorless sensors.  One of the ways they focused on making this a true digital lens was lowering the amount of micro-contrast, which is something that is often tuned up on lenses that are designed to work with film, since it can be a very effective feature in film, but tends to leave skintones looking too crispy in digital.

That does leave us wondering if perhaps someone might eventually make an LPL mount for a non-reflex motion picture camera like the Mitchel: we’d be very curious to see how signature primes pair with a modern film stock.  

Telecentricity

Another feature to make this a true digital lens was Arri’s focus on telecentricity.  As light exits the back of a lens, it “spreads” out in all directions. In a truly telecentric lens (and these aren’t, but they are close), the light waves come out the back of the lens parallel.  In the Signature primes, they are very, very close to parallel.

Why does this matter in digital sensors? It all has to do with chromatic aberration, with is that color fringing you sometimes see at the edge of a high contract image, where it gets an orange/blue halo (primary aberration) or even worse sometimes a green/magenta halo (known as secondary aberration).

Aberration has to do with the different wavelengths of light traveling at different angels as they are refracted through the lens.  With the Signatures Arri has worked very hard to ensure that the aberration itself is very minimal, and mostly primary warm/cool aberration since that tends to look more natural when it does appear.  However, many of you might have noticed that aberration isn’t just an aspect of the lens, it’s also affected by the sensor.

The reason why goes back to that bending of light.  If you have a sensor with far apart photosites, chromatic aberration will look differently than if they are next to each other, since the light is getting bent, and some wavelengths are landing on the next photosite over.

In the wonderful drawings below you see two lenses, one telecentric (with the red, green and blue light staying roughly parallel), and then one less telecentric.  As the light spreads, the different wavelengths of red, green and blue light spread differently from each other.  This is one of the fundamentals of lens design, and is is why different lenses aberate differently on different sensors.

 

As you can see in the image above (credit to Charles Haine), with a telecentric lens the red, green and blue light is more likely to land on the same photosite on the sensor, whereas on the left, with the light splaying out, the red, green and blue light lands on different photosites.  This is why lenses that might have had no aberration suddenly had a lot in digital, since film doesn't have discrete photosites.   Or you might have noticed a lens that aberrated a lot on one camera and not much at all, or a different color, on another.  Aberration is an interplay of the lens and the sensor together.

This is why Arri focused on a telecentric lens design.  By focusing on getting the light coming out of the back of the lens as parallel as possible, aberration is minimized since it’s more likely that different wavelengths/colors still end up hitting the same photosite. Thus if you move the Signature primes to other sensors, with LPL mounts coming for RED and Sony cameras among others, the aberration should still consistent and very minimal.  Even as photosites get smaller and smaller in the future, there will likely always be gaps between them, and Arri is focused on creating lenses that should perform well for at least the next decade, if not even longer.

One neat way to see if a lens is telecentric (or near telecentric) is to look through the body of the lens.  You should see the focus blades appear to be near the front of the lens if it’s a telecentric lens, if the focus blades appear to be near the back of the lens, it’s not likely a telecentric design.

LPL mount is the future of Arri, and they hope the industry

Arriflex have announced that the LPL is now their new standard, and they have made it open for all to use.  Even their upcoming Super35mm sensor (likely late 2020/early 2021) will be built around LPL.  This is because LPL, with it’s larger entrance pupil and it’s shorter flange focal distance, let’s them design lenses that simply couldn’t exist in the class PL mount days.  Every new Arri camera here on out with be LPL native, and Arri rental is converting Alexa65 cameras over to LPL.

It's bigger than just Arri, however; the goal is that the way PL became the default mount for the (non-Panavision) film industry, LPL will become the default mount moving forward.  While Arri does require signing a license to work with LPL to ensure quality standards, there is no fee on the license and a diverse array of manufacturers are already committed to the format.

Physical Build

It seems funny to leave “physical build” for the end, but there really is so much to talk about with the images they create that is is hard to remember to talk about the lenses themselves.  First off, they are surprisingly lightweight. The lens bodies are made of magnesium, with glow in the dark markings, and they feel like lenses you could comfortably fly on a steadicam all day, something you would never have said about the Master Primes (and they didn’t even cover full frame!).  Focus and Iris ramps are smooth and silky, the whole unit feels very durable, but it’s truly the weight that is the standout.  

Another difference with the Masters is maintenance.  While the Master Primes were truly the most sought after lenses of their period, they were apparently difficult to maintain (though I'm not a lens tech and can't speak to precisely why, it is something I have heard frequently).  Arri have focused with the Signature lenses on creating glass that is easier to maintain, both by the lens techs in rental houses, and also by creating Level 2 lens service centers for more complicated work in Munich, Burbank, Hong Kong and Beijing. The signature primes have a two layer design, with all the lens elements and mechanics like the focus cam and aperture system in the inner barrel, and an outer barrel with a protective shell.  This makes it easier to change out the shell, if for instance there has been minor cosmetic damage, or to change from imperial to metric, without affecting the mechanical aspects of the internal barrel.

Conclusion

Overall the only feeling you walk away with from the Signature primes is that they are stunning.  They don’t feel really soft or sharp, as Roger Deakins said they feel “clear,” like they aren’t getting between you and the scene.  There is the tiniest bit of warmth, a really nice skintone reproduction, and a focus on the future that make these lenses a sea change for the industry that is likely to dominate and be imitated for a long time to come.  These feel like the first set of lenses signally the next generation of lens design.

 

Special thanks to the administration and students at Brooklyn College Feirstein Graduate School of Cinema.

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