Production

Quick Look: Signature Primes

A brief review of ARRI’s new LPL-mount large-format cine lenses

ARRI is now shipping Signature Primes, lenses “designed to render organic, emotionally engaging images, gently softening and texturizing the large format with natural skin tones and creamy bokeh.” Signatures Primes are large format lenses using ARRI’s new LPL mount. They cover at least a 44.7mm image circle, sufficient for Alexa LF open gate; Abel Cine lists the image circle as 45mm.

There are 16 lenses in the set, from 12mm to 280mm; all are currently available aside from the 12mm, 15mm, 200mm, and 280mm. The 200mm and 280mm are expected by the end of  July, the 15mm should ship in late August, and the 12mm is scheduled for the end of November.

Signature Primes are fast: T1.8 from 12mm through 150mm, T2.5 on the 200mm and T2.8 on the 280mm. While T1.8 may not seem extreme, f/1.8 is roughly the full-frame depth of field equivalent (for a given angle of view) to f/1.3 on S35mm-sized sensors — think Zeiss Super Speeds or ARRI Master Primes — or f/0.9 on micro four thirds — Voigtlander Nokton territory.

A six-lens set lists for $153,290, while individual lenses start at around $25,000 for the “cheap” ones in the middle, rising to $40,000 for the 12mm and 280mm. In price, as well as in effective depth of field control, these would seem to be the large-format counterparts of Master Primes: fast, sharp lenses with low distortion, minimal breathing, and few aberrations. Yet the Signatures are being pitched as having a more face-friendly rendering — that “gently softening and texturizing” stuff — as opposed to the crisper, more “clinical” look of Masters. 

ARRI sent me a set of 11 Signature Primes to look at: 

11 in a row: 18mm, 21mm, 25mm, 29mm, 35mm, 40mm, 47mm, 58mm, 75mm, 125mm, and 150mm, all T1.8

Well, they sent the lenses to our local (and exceedingly helpful) rental house, Koerner Camera Systems, because Koerner’s insurance can cover a third of a million dollars worth of cinema glass whereas mine cannot. I spent the better part of a day at Koerner, taking a quick look at Signatures from 18mm to 150mm on a 7.9K (7952 x 5304) full-frame Sony A7Riii camera. I wasn’t able to exhaustively test the entire set, but I was able to get a feel for them overall, and run a few of the lenses through several tests.

Design

Signature Primes are large lenses, but not especially heavy for their size: magnesium housings add lightness. From 18mm through 125mm the lenses are 178mm / 7.01 inches from flange to front, with a 114mm front diameter and a maximum housing diameter only 1mm wider. Weights cluster around 1.9 kg / 4.2 pounds. Lenses at the extreme ends of the range tend to be longer, fatter, and/or heavier, but iris and focus gears are in the same places on all.

11 Signature Primes
Ten same-sized Primes, plus the 150mm. Height variations in the ten are due to different rear lens cap thicknesses.

Focus and iris scales are marked in day-glo green paint, on both sides of the lens.

Side view, Signature Prime

Iris throw is about 45º, though the large diameter of the lens barrel makes that less cramped than it sounds. Focus throw is about 300º or so (maybe more; I didn’t measure it), with left and right scales visible through offset windows on each side, so there’s no possible confusion about which scale to use: you only see the scale for your side of the lens.

Right side of Prime showing offset focus windows

Witness marks for the focus scales are on the surrounding, fixed housing, which means that parallax errors are possible: a mark lined up when looking right at the lens won’t be perfectly lined up when looking up or down at it. This isn’t a showstopper, but it’s something to be aware of if you’re focusing to marks wide-open.

Side view, Signature Prime, on the level
Signature Prime, on the level
The same lens, from 30 degrees above
The same lens from 30º above; note the apparent shift in the focus setting

Lenses are available in either Imperial or metric scales, of course.

Focal length and maximum aperture are emblazoned on both sides of the lens in day-glo green, making the lens easy to identify.

The top and bottom of the housing have two fine-pitch tapped mounting holes. When I asked ARRI Cinema Lens Specialist Art Adams what they were for, he said, “They are undefined accessory mounting points. The thinking is this: ‘Lenses are round. Crew may wish to attach things to this round surface. Let’s make that easy.’”

Signature Primes, top and bottom

The bottom of the lens also bears the legend “Made in Japan”; these are not Zeiss lenses sold under the ARRI label, but ARRI-designed optics manufactured under contract (speculating on the identity of the contract manufacturer is left as an exercise for the reader).

(Art Adams adds, for the sake of completeness: “Technically, we specify what we want to see in the lenses, often in documents that run 100-200 pages, and then the contractor builds the lenses to meet those specs. But we don’t fully design them in-house.”)

You’ll also find a GS1 GTIN identifier, the lens’s serial number, and both combined in a matrix code, which ARRI says, “can be identified globally and makes rental check-ins and check-outs easier. They provide proof of ownership and eliminate the need for stickers that can fall off or leave residue.” 

Signature Primes use ARRI’s LPL mount. LPL’s 62mm diameter and 44mm flange depth are designed specifically for modern large-format cameras unencumbered by spinning-mirror shutters. 

LPL mounts and adapters
LPL mounts for ARRI mini LF and Sony VENICE; LPL-to-E-mount adapter, and a PL-to-E adapter for comparison

The LPL mount includes ARRI’s LDS-2, an updated Lens Data System fully implemented in the Signature Primes. The four LDS-2 contacts reside at the top of the mounting flange.

Rear of Signature Prime showing LDS-2 contacts

Each Signature Prime has a rear mounted, magnetically attached net holder: a removable, grooved ring. 

Signature Primes with net holder on and off
Net holder is on the left lens, removed from the right lens

The net holder lets you easily attach rear diffusion or filtration media using a rubber band. ARRI sent a few samples along with the lenses:

Signature Prime rear nets

Nets fitted to Signature Primes

Internally the Signatures use an 11-blade iris. Expect 22-point sunstars.

Signature Prime iris

Signatures come in elegant aluminum cases.

Signature Prime shipping case

Signature Prime shipping case

They are lockable and stackable, and include a slot for the printed User Manual. However, Arri warns, “[d]o not put the case underwater.” Imagining what circumstance led ARRI into making this warning is, again, left as an exercise for the reader.

The cases are somewhat bulky and you may well find Signature Primes in the wild are carried instead in industry-standard six-hole shipping cases.

Signature Prime shipping case and standard six-hole case

Performance

I only had a few hours to run tests, so I wasn’t able to do a comprehensive evaluation. That’s why this is a Quick Look, not a proper Review. Anyway…

Sharpness

TL;DR version: these suckers are sharp, beyond my ability to measure them with a mere 7.9K sensor. I would have loved to put a Signature on Koerner’s projector, but we didn’t have an LPL mount for it.

Here’s a pixel-for-pixel crop from the center of a test chart, shot with the 47mm at both T1.8 and T4. Remember, this is a 700 x 700 detail from a 7952 x 5304 image.

47mm @ T1.8, pixel-for-pixel crop
47mm @ T1.8, pixel-for-pixel crop
47mm @ T4, pixel-for-pixel crop
47mm @ T4, pixel-for-pixel crop

If you download them and flip between them, you’ll probably be able to detect that the T4 image is ever so slightly crisper than the T1.8 image, but only ever so slightly. Normally, a fast, wide-open lens is visibly soft compared to a couple stops down; here the difference is minuscule. 

What’s more, corners seem just as sharp as the center at most apertures; wide open the corners are visibly softer — but not by much. These are T1.8 and T4 samples from the upper left corner of the chart:

47mm @ T1.8, pixel-for-pixel corner crop
47mm @ T1.8, pixel-for-pixel corner crop
47mm @ T4, pixel-for-pixel corner crop
47mm @ T4, pixel-for-pixel corner crop

I shot this chart from wide open to T22 on three lenses, the 25mm, 47mm, and 125mm, and got essentially identical results on all three. The lenses are almost imperceptibly less crisp wide open, and starting around T11 to T16 diffraction starts reducing sharpness (as it will for any lens; it’s a physical limit), but extremes aside it’s well-nigh impossible to tell the different shots apart based on sharpness.

Chromatic Aberration

Here’s a pixel-for-pixel from of the lower left corner of the chart from the 47mm at T4:

47mm @T4, corner crop

There’s a faint lateral chromatic aberration (CA): a mild yellow/blue fringing, maybe a couple pixels in width (you can also see it in the upper-left images above). That is absolutely the worst I saw on any lens I looked at.

How about axial CA, a.k.a. longitudinal CA? That’s the (typically) green/magenta fringing you’ll see on contrasty edges as you focus past them. Here’s a sample from the 75mm, wide-open, with pixel-for-pixel grabs focused just in front of and just behind the chart:

75mm @T1.8, focused both near and far

Yes, it’s there if you’re looking for it, but it’s so mild it’s negligible.

I was also able to see it on the resolution chart, but not pixel-for-pixel: with the chart zoomed to fit in Capture One, flipping between the just-in-front and just-behind images showed a faint green / magenta shift on the zone plates overall; something about the resampling made it show up more than when I was zoomed in to pixel-level detail, where it was imperceptible. 

Again, this was a worst-case sample; I noted “minimal axial CA” on the 25mm, 29mm, and 75mm, but I didn’t see anything noticeable with the other focal lengths, looking at magnified pix on the A7Riii’s LCD or those same magnified pix fed to a PIX-E5 monitor/recorder. That’s not to say that there is none whatsoever, but whatever might be there is so minimal as to be visually insignificant.

From a chromatic aberration standpoint, these lenses are darned clean.

Illumination / Vignetting

I measured illumination falloff on the 25mm, 47mm, and 125mm. Wide open, the 25mm’s corners are 1 and 1/3 stops darker than the center; by T2.8 and 2/3 illumination is flat across the entire frame. For the 47mm, corners are also 1 and 1/3 stops darker wide open; clean by T4. The 125mm has corners a stop darker when wide and even illumination by T2.8 and 1/3.

47mm at T1.8

47mm at T4

I looked at the rest of the set and saw comparable performance, though I didn’t record measurements.

Geometry

The lenses look pretty much rectilinear when focused to infinity. Pulling focus nearer on the 125mm and 47mm showed essentially the same thing. Have a look at the 47mm’s vignetting shots above; I wasn’t perfectly perpendicular to the chart, but straight lines are still straight.

Focusing closer on the 18mm and 25mm showed slight barrel distortion. Bear in mind that these are wide lenses on full frame; here’s where the chart was to fill the image on the 18mm:

Shooting the chart with the 18mm

Getting highly rectilinear images from very wide lenses is rare; it’s a difficult thing to accomplish.

You can see all four lenses at infinity and at minimum objective distance (M.O.D., the nearest-focus setting) in the next section.

Focus Breathing

Focus breathing is the change in image size (or magnification) when the focus is changed. Lenses of conventional design (by which I mean designs in which the entire lens moves in and out to adjust focus) enlarge the image when they’re focused more closely. Many modern designs “float” some elements with respect to others, and their breathing can be quite different.

I saw normal or “positive” breathing on the 150mm and 125mm, slight positive breathing on the 58mm, essentially no breathing on the 29mm, 35mm, and 75mm, slight negative breathing on the 40mm and 47mm and strong negative breathing on the 18mm, 21mm, and 25mm. I’ve never seen negative focus breathing before.

Here are grabs from the 18mm, 25mm, 47mm, and 125mm, with M.O.D. (near) focus on the left and infinity focus on the right:

125mm; M.O.D on left, Infinity on right

47mm; M.O.D on left, Infinity on right

25mm; M.O.D on left, Infinity on right

18mm; M.O.D on left, Infinity on right

Focus Ramping

Focus ramping is a change in exposure as focus is changed. Conventional lenses, if uncompensated, typically darken by 1/6 to 1/3 stop when focused to M.O.D compared to infinity focus.

Signature Primes don’t. Exposure remains constant as the lenses are focused through their entire ranges.

Flare and Sunstars

Signature Primes seem to be resistant to veiling flare and only rarely does any “focused” flare appear. 

If you look at the breathing shots above, there’s a diagonal flare on the upper left corner on the 18mm at M.O.D and 125mm; at infinity Koerner’s test bays have overhead light bars running the length of the bay on either side, and I seem to have gotten the camera position just right (slightly off-center, which is why I’m not square to the chart on its overhead track) to catch some light at a corner of the lens. 

When I shone a light directly into the lens (the LED on an iPhone) I was sometimes able to get a radial ghost or two, but these were small and mild. If you’re looking for a glorious constellation of ‘70s-style zoom-lens flares, look elsewhere.

Ah, but sunstars… remember those 11-blade irises? Once you stop down below T4, gorgeous 22-point sunstars start blooming…

Sunstar, 47mm at T2.8 Sunstar, 47mm at T4 Sunstar, 47mm at T5.6 Sunstar, 47mm at T8 Sunstar, 47mm at T11 Sunstar, 47mm at T16 Sunstar, 47mm at T22 Sunstar, 75mm at T8 Sunstar, 40mm at T5,6

Nets

Want the look of sunstars, but with variations? Or when shooting at wider apertures? Or do you just want to soften and flare the image a bit? Those behind-the-lens nets can help, as these two T1.8 shots show, with silver and black nets respectively:

Using a behind-the-lens net Using a behind-the-lens net

Bokeh, General Rendering

Bokeh was smooth and neutral, whether the out of focus element was before or behind the plane of focus. I didn’t see any obvious “onion rings”, “donuts”, or other bokeh busyness, just pleasingly soft blobs.

When I looked at Canon Sumires, I found that close-ups of lens markings — sharp bright details on a dark, textured background — were useful indicators of things like spherical aberration. In the Sumires, wide open, those bright details “bloomed” and the barrel’s fine texture softened. So I tried the same thing with Signature Primes:

47mm @ T4, pixel-for-pixel
47mm @ T4, pixel-for-pixel

It didn’t matter whether I was wide open or stopped down, the rendering was always the same: sharp yet neutral. That “gently softening and texturizing” characteristic that ARRI claims for the Signatures is a subtle thing — fine detail was present but not overemphasized — and one not obviously affected by aperture settings.

To put this in context, ARRI’s Art Adams describes the motivation behind Signature Primes:

“Signature Primes are high resolution lenses but they don’t create unnaturally crisp images. We’ve put a lot of emphasis on reproducing skin beautifully and naturally, but without appearing classically sharp. The bokeh is unusually soft, for increased depth separation. And we’ve tried to eliminate or minimize all the aberrations that are enhanced when images are viewed in UHD and HDR, such as chromatic aberration, edge softness, focus ramping, and focus breathing.
“We intend these to be ‘all-format’ lenses. They capture high resolution imagery for both large format and traditional Super 35 sensors while rendering a consistent look across all focal lengths.”

Beyond that, deponent sayeth not: I didn’t perform a side-by-side with other lenses, and I’m not qualified to pontificate on how well a lens can “reproduce skin beautifully and naturally, but without appearing classically sharp” without doing a direct comparison with other lenses that supposedly do — or don’t.

But I can shoot pictures, so that’s what I did instead. I dragooned “Malo” Chelsea Smith, a flex-tech at Koerner when she’s between productions, to sit in front of the camera, and I ran through the focal lengths from 18mm through 125mm, all at T1.8.

18mm at T1.8 21mm at T1.8 25mm at T1.8 29mm at T1.8 35mm at T1.8 40mm at T1.8 47mm at T1.8 58mm at T1.8 75mm at T1.8 125mm at T1.8

Conclusion

Signature Primes are fast, large format lenses with rectilinear geometry, vanishingly low chromatic aberration, little flare, and pleasing bokeh. They appear to be more than sharp enough for 8K imaging when pixel-peeped, yet the images feel unforced and natural.

Image rendering is remarkably consistent through the aperture range when it comes to sharpness and contrast across the frame. Corners darken wide-open (in effect, you have a vignetting control along with your depth-of-field control), as is common with fast lenses, and apertures below T4 show visible 22-point sunstars on light sources.

In short, they make attractive and consistent images, aperture to aperture, and lens to lens. If you’re shooting large format, they’re well worth looking into.


More info: download the Signature Prime User Manual (PDF).


Disclosure: I’ve known ARRI’s Art Adams for many years, but there is no material relationship between me and ARRI. ARRI offered me no payment or other consideration for a favorable review. Similarly, Koerner Camera Systems always makes me feel welcome, but didn’t encourage me to mention them in any way. I did so anyway, because they’re friendly and helpful and they deserve a shout-out.

Signature Prime hero shot


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PVC Staff
Adam Wilt has been working off and on in film and video for the past thirty years, while paying the bills writing software for animation, automation, broadcast graphics, and real-time control for companies including Abekas,…

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Stuart Brereton

The difference in DoF between FF and s35 is more like 1 1/3 stop, Adam, surely. PCAM tells me this also 🙂