Spherical Lens Tests

The other week I spent a day at Arri Rental in Uxbridge, in the Bafta Room no less, conducting various camera and lens tests. I’ve done a number a productions now where I wanted to test but there wasn’t the time or money, so for a while I’ve been meaning to go into Arri on my own time and do some general tests for my education and edification. An upcoming short provided the catalyst for me to get around to it at last.

Aided by 1st AC Rupert Peddle and 2nd AC Bex Clives, I tested a dozen lenses, some spherical, some anamorphic. Today I will cover the spherical lenses; next time I’ll look at the anamorphics.

 

Method

We shot on an Alexa XT Plus in log C ProRes 4444 XQ at 3.2K. In the video the image has been downscaled to 1080P and a standard Rec.709 LUT has been added.

I set the Alexa to ISO 800 and lit Bex to a T2.8 using a 650W tungsten fresnel bounced off poly. For fill I caught a little of the spill from the fresnel with a matte silver bounce board on the opposite side of camera. I placed fairy lights in the background to observe the bokeh (out of focus areas) and turned on a 100W globe during each take to see what the flare did.

We shot all the lenses at 2.8 – the stop I most commonly use – and also wide open (compensating with the shutter angle), but the direct 2.8 comparison proved most useful, so that’s mainly what you’ll see in the video. We tested a single length: 35mm or the closest available to it.

What we didn’t do was shoot grey-scale or colour charts, or do any testing of vignettes or distortion. (The day after doing these tests, Shane Hurlbut, ASC published an Inner Circle post about how to tests lenses, so I immediately learnt what my omissions were!)

We tested the following lenses:

Series Length Speed CF* Weight Price
Leica Summilux-C 29mm T1.4 18″ 1.7kg £27K
Arri/Zeiss Master Prime 35mm T1.3 14″ 2.2kg £16K
Cooke S4 32mm T2 6″ 1.85kg £14K
Leica Summicron-C 35mm T2 14″ 1.3kg £13K
Zeiss High Speed
(a.k.a. Superspeed Mk III)
35mm T1.3 14″ 0.79kg £12K
(refurb)
Arri/Zeiss Ultra Prime 32mm T1.9 15″ 1.1kg £10K
Zeiss T2.1 32mm T2.1 24″ 0.45kg £4K
(used)
Canon 35mm T1.5 12″ 1.1kg £3K

* CF = close focus

Here’s the video…

 

Skin tones

Click the image to see it at best quality.

The Arri/Zeiss Master Prime and the two Leicas seem to have the most vibrant skin tones. To my eye, the Leicas have a slight creaminess that’s very pleasing. The Canon looks just a little cooler and less dynamic. I was surprised to find that the Cooke S4, the lens I’ve used most, appears to have a grey, flat skin tone compared with the Master Prime, Leicas and Canon. I would rank the Ultra Prime and Superspeed next, on a par except that the Ultra Prime has a noticeable magenta cast. My least favourite skin tones are on the Zeiss T2.1, which comparatively makes poor Bex look a little bit ill!

Some of the nuances will be lost in the YouTube and Jpeg compression, but this is a very subjective assessment anyway, so feel free to completely disagree with all of the above. Any of the differences noted above could be corrected by grading, to some extent . But remember that the lens is at the very start of the light’s journey from set to screen, and any wavelengths that don’t get through it are lost forever. It’s like fluorescent lamps with colours missing from the spectrum; you can’t put those back in in post.

 

Sharpness

I have to say, I’m unable to detect any difference in sharpness between the Master Prime, Cooke S4, Canon and Leicas. The Ultra Prime and Superspeed both look a hair softer, while the T2.1 is very soft.

 

Breathing

Breathing is the slight zooming effect that you get with some lenses when you pull focus. Looking at 4:44 in the video you can clearly see the differences in breathing between the eight lenses. Because this part of the video is showing a crop of the bottom left corner of the image, the breathing manifests as a shift to the left (zoom in) as the lens is racked closer (goes soft) and a shift to the right (zoom out) as it’s racked deeper (goes sharp).

All the Zeiss lenses except the Master Prime have a significant amount of breath when seen in isolation like this, but not enough to be noticeable to an audience in most real-world situations. The Cooke S4 has a little bit of breathe, and the Canon a hair less. The Master Prime and the Leicas are rock solid.

 

Bokeh

Small points of light, when thrown out of focus, most clearly demonstrate the bokeh pattern of a lens. The shape of the bokeh is determined by the number of iris blades and the shape of those blades. Generally a circle is preferred, because it’s a natural shape, but for certain stories a more unusual shape might be appropriate. The shape of the iris changes with the T-stop, hence the T2.8 and wide open images above.

Immediately noticeable is the difference in the Cooke S4’s bokeh between wide open (circular) and T2.8 (octagonal). All of the other lenses have round bokeh at T2.8, apart from the Superspeed, which has heptagonal (seven-sided) bokeh.

It’s entirely subjective which bokeh you prefer. The only other thing I’ll point out is that the Canon’s bokeh wide open is very fuzzy, with noticeable colour aberration, though this may be due to the bright highlight rather than the defocusing.

 

Flare

Flare patterns also vary with aperture. The smaller the aperture, the more of a star effect you will get, as the light interacts with the corners in the iris blades. The Summilux shows this most clearly, with a pronounced star at T2.8 (two stops down from its maximum aperture) and almost none when wide open. The Cooke S4 also has a nice star pattern at T2.8. With the other lenses it’s much more subtle, and the Canon has almost none.

 

Conclusions

The real revelations in these tests, for me, were the Leicas. The Summilux in particular is a beautiful lens, with rich, dynamic skin tones, nice bokeh, no breathing, plus the bonus of nice star flares. I will definitely be looking to work with this glass in the future, although given the price tag that may be optimistic!

The Summicron also performed incredibly well, matching the more expensive Summilux and Master Prime in every respect except speed. I can see this becoming my new go-to lens.

The Master Prime of course produced a beautiful, sharp, clean image, but it lacks character. It might work nicely for science fiction, a drama requiring a neutral look, or something where filtration was being used to give the image character.

The Canon impressed me too – no mean feat given that it’s the cheapest lens we tested. With nice skin tones and attractive flares, I could see this working well for a romantic movie.

The Zeiss T2.1 did not appeal to me, with poor sharpness and cold, washed-out skin tones, so I would avoid it.

The Superspeed is a decent lens, but in most cases I’d plump for an Ultra Prime instead. Ultra Primes are certainly easier to work with for the 1st AC, and have proven to be a good workhorse lens for drama. (I shot Above the Clouds on them.)

The Cooke S4 has been my go-to glass up to now, and while it will probably remain my first choice for period pieces, due to its gentle focus fall-off, I’m excited to try some of the other glass in this test on other productions.

I’ll say it one last time: this is all subjective. Our visual preferences are what make every director of photography unique.

Tune in next week when I’ll look at the anamorphic lenses: Hawk-V, Cooke Xtal and Kowa Mirrorscope.

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Spherical Lens Tests

Alexa ProRes ISO Tests

My Cousin Rachel

I’ve shot three features on Arri Alexas, but I’ve never moved the ISO away from its native setting of 800 for fear of noise and general image degradation. Recently I read an article about the cinematography of My Cousin Rachel, in which DP Mike Eley mentioned shooting the night scenes at ISO 1600. I deliberately set off for the cinema in order to analyse the image quality of this ISO on the big screen. Undoubtedly I’ve unwittingly seen many things that were shot on an Alexa at ISO 1600 over the past few years, but this was the first time I’d given it any real thought.

To my eye, My Cousin Rachel looked great. So when I was at Arri Rental the other week testing some lenses, I decided to shoot a quick ISO test to see exactly what would happen when I moved away from the native 800.

But before we get to the test footage, for those of you unsure exactly what ISO is, here’s an introduction. The more experienced amongst you may wish to skip down to the video and analysis.

 

What is ISO?

ISO is a measure of a camera’s light sensitivity; the higher the ISO, the less light it requires to expose an image.

The acronym actually stands for International Organization for Standardization [sic], the body which in 1974 combined the old ASA (American Standards Association) units of film speed with the German DIN standard. That’s why you’ll often hear the terms ISO and ASA used interchangeably. On some cameras, like the Alexa, you’ll see it called EI (Exposure Index) in the menus.

A common ISO to shoot at today is 800. One way of defining ISO 800 is that it’s the sensitivity required to correctly expose a key-light of 3 foot-candles with a lens of T-stop 1.4 and a 180° shutter at 24fps, as we saw in my Barry Lyndon blog.

If we double the ISO we double the effective sensitivity of the camera, or halve the amount of light it requires. So at ISO 1600 we would only need 1.5 foot-candles of light (all the other settings being the same), and at ISO 3200 we would need just 0.75 foot-candles. Conversely, at ISO 400 we would need 6 foot-candles, or 12 at ISO 200. Check out this exposure chart if it’s still unclear.

ISO is one of the three corners of the Exposure Triangle, well-known to stills photographers the world over. You can read my posts on the other two corners: Understanding Shutter Angles and F-stops, T-stops and Optical Density.

Just as altering the shutter angle (exposure time) has the side effect of changing the amount of motion blur, and altering the aperture affects the depth of field, so ISO has its own side effect: noise. Increase the ISO and you increase the electronic noise in the picture.

This is because turning the ISO up causes the camera to electronically boost the signals it’s receiving from the sensor. It’s exactly the same as turning up the volume on an amplifier; you hear more hiss because the noise floor is being boosted along with the signal itself.

I remember the days of Mini-DV cameras, which instead of ISO had gain; my Canon XL1 had gain settings of -3dB, +6dB and +12dB. It was the exact same thing, just with a different name. What the XL1 called 0dB of gain was what today we call the native ISO. It’s the ISO at which the camera is designed to give the best images.

 

ISO and Dynamic Range

The Alexa has a dynamic range of 14 stops. That means it can simultaneously record detail in an area of brightness x and an area of brightness times 2 to the power 14. At its native ISO of 800, those 14 stops of dynamic range are equally distributed above and below “correct” exposure (known as middle grey), so you can overexpose by up to 7 stops, and underexpose by up to 7 stops, without losing detail.

If you increase the ISO, those limits of under- and overexposure still apply, but they’re effectively shifted around middle grey, as the graphic to the left illustrates. (The Pro Video Coalition post this graphic comes from is a great read if you want more detail.) You will see the effects of this shifting of dynamic range very clearly in the test video and images below.

In principle, shooting at ISO 1600 is the same as shooting at ISO 800, underexposing by a stop (giving you more highlight detail) and then bringing it back up a stop in post. The boosting of the signal in that case would come right at the end of the image path instead of near the beginning, so the results would never be identical, but they’d be close. If you were on a bigger project with a DIT, you could create a LUT to bring the exposure up a stop which again would achieve much the same thing.

All of the above assumes you’re shooting log ProRes. If you’re shooting Raw then everything is simply recorded at the native ISO and any other ISO you select is merely metadata. But again, assuming you exposed for that other ISO (in terms of iris, shutter and ND filters), you will effectively get that same dynamic range shift, just further along the pipeline.

If this all got a bit too technical for you, don’t worry. Just remember:

Doubling the ISO

  • increases overall exposure by one stop,
  • gives you one more stop of detail in the highlights,
  • gives you one less stop of detail in the shadows, and
  • increases picture noise.

Halving the ISO

  • decreases overall exposure by one stop,
  • gives you one less stop of detail in the highlights,
  • gives you one more stop of detail in the shadows, and
  • decreases picture noise.

 

The Test

I lit the subject, Rupert “Are You Ready?” Peddle, with a 650W tungsten fresnel bounced off poly, and placed a 40W candle globe and some LED fairy lights in the background to show highlight clipping. We shot the tests in ProRes 4444 XQ on an Alexa XT Plus with a 32mm Cooke S4, altering the shutter angle to compensate for the changing ISOs. At ISO 400 the shutter angle was maxed out, so we opened the lens a stop for ISO 200.

We tested five settings, the ones corresponding to a series of stops (i.e. doublings or halvings of sensitivity): 200, 400, 800, 1600 and 3200. I have presented the tests in the video both as recorded in the original log C (mislabelled as S-log, sorry!), and with a standard Rec.709 LUT.

You’ll need to watch the video at full-screen at 1080P to have any chance of seeing the differences, and even then you might see the compression artefacts caused by the noise more than the noise itself. Check out the stills below for a clearer picture of what’s going on. (Click on them for full resolution.)

 

Analysis

To me, the most important thing with every test is how skin tones are rendered. Looking at the original ProRes of these comparisons I think I see a little more life and vibrance in the skin tones at lower ISOs, but it’s extremely subtle. More noticeable is a magenta shift at the lower ISOs versus a green shift at higher ones. The contrast also increases with the ISO, as you can see most clearly in the log images.

At the lower ISOs you are not really aware of any noise in the picture. It’s only at ISO 1600 that it becomes noticeable, but I have to say that I really liked this level of noise; it gives the image a texture reminiscent of film grain. At ISO 3200 the noise is quite significant, and would probably be unacceptable to many people.

The really interesting thing for me was the shifting of the dynamic range. In the above comparison image, look at the globe in log – see how it starts off as one big white blob at ISO 200 and becomes more detailed as the ISO rises? Now look at the dark wall around the globe, both here and in the previous image – see how it subtly and smoothly graduates into darkness at the lower ISOs, but becomes a grainy mess at the higher ones?

I can see an immediate benefit to shooting at ISO 1600 in scenes lit predominantly with practicals. Such scenes tend to have a low overall level of illumination, while the practicals themselves often blow out on camera. Going to ISO 1600 would give me extra exposure and extra detail in the practicals. I would be sacrificing shadow detail, so I would have to be a little more careful not to underexpose any faces or other important elements of the frame, but I can deal with that. In fact, I often find myself determining my exposure in these types of scenes by how blown out the practicals are, wishing I could open up a little more to see the faces better but not wanting to turn the lamps into big white blobs. Increasing the ISO would be the perfect solution, so I’m very glad I did this test to alleviate my ungrounded fears.

What about scenarios in which a lower-than-native ISO would be useful? Perhaps a scene outside a building with an open door, where the dark interior is visible in the background and more detail is required in it. Or maybe one of those night scenes which in reality would be pitch black but for movie purposes have a low level of ambient light with no highlights.

I hope you’ve found this test as useful and interesting as I have. Watch this space or subscribe to my YouTube Channel for the lens test.

Thanks to Rupert Peddle, awesome steadicam op and focus puller – check out his site at pedhead.net – for appearing in front of the lens. Thanks also to Bex Clives, who was busy wrangling data from the lens tests while we were shooting these ISO tests, and of course Arri Rental UK.

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Alexa ProRes ISO Tests

“Above the Clouds”: Summer 2017 Pick-ups

This time last year, principal photography had just wrapped on Above the Clouds, a comedy road movie directed by Leon Chambers. We always knew that there would be additional photography, and several days of this have been scattered over the past year.

In May I spent a few odd days with Leon and the Yellow Peril, primarily capturing car-to-car tracking shots. Leon had already shot some of these without me up in Cumbria, so he had the technique down. He attached his Blackmagic Micro Cinema Camera to his roof rack with clamps and suction cups – three points of contact in all, to eliminate vibrations.

The focus was left fixed at the approximate distance the cars would be apart, and I could reach out of the passenger window and tweak it, along with the variable ND filter, if necessary. Recording was triggered from the custom remote which Leon had made for the camera last year when we used it for the autumn pick-ups. I monitored on a 5″ Blackmagic Video Assist which – thanks to a firmware update – now has a false colour display, which was very useful for keeping an eye on the exposure.

We had no means of panning or tilting the camera during takes, so we would frame the car centrally, allowing the maximum space to each side for when we went around the bends. This had the nice effect of making the Peril look small in the landscape, surrounded by it on all sides.

And speaking of the Peril looking small, it had shrunk considerably when I next saw it. But so had the landscape.

To keep the audience informed of the characters’ progress across Great Britain, Leon planned to cut to a map at a few strategic moments. At some point the original plan of shooting an Ordnance Survey map on a wall turned into something much more elaborate, a work of art featuring found objects, such as the lead character Charlie might have made herself.

Leon knew he wanted to use his jib to drift the camera over the map. But what camera? We both agreed that these shots needed to have a noticeably different look to the rest of the movie. Both Super-8 and Super-16 were discussed, but ultimately neither were viable. Then I suggested shooting on a full-frame DSLR to get a tiny depth of field. I imagined the camera having fixed focus as it skimmed over the map, with features coming in and out of focus as they passed through the field. We didn’t end up doing that, but Leon did like the DSLR idea.

Asahi Pentax-M 50mm/f1.4

So the decision was made to shoot on a Canon 5D Mk III belonging to focus puller Max Quinton. We ended up shooting everything on a single lens, my Asahi Pentax-M 50mm/f1.4. This is a vintage K-mount stills lens which is beautifully sharp, and we mounted it with a passive EF adapter. 50mm on full-frame is equivalent to 35mm on Super 35, very close to the 32mm which was our most used lens length during principal photography.

I added a half Soft FX filter as I usually do. I had briefly considered omitting it, to further differentiate the map shots from the rest of the film, but undiffused shots in a mostly diffused movie draw attention to the filtration and can be quite jarring.

I offered Leon two options for the lighting. One was to simulate the natural light you would see if shooting the British Isles from a high altitude, i.e. a hard sun source and ambient toplight. The other, which he went for, was to carry on the suggestion of Charlie making the map herself, and make it look like she had lit it herself too, with an eclectic mix of practicals around the edge. A couple of tungsten Chinese lanterns were hung overhead as well for soft fill. To help the camera’s limited dynamic range, I put tough-spun diffuser inside some of the practicals’ shades, on the camera side.

The Blackmagic 5″ Video Assist can be seen here mounted on the back of the camera.

There were a couple of “night” scenes on the shot list. For these we turned off the Chinese lanterns and turned on a desk-lamp practical with a blue-ish LED bulb to suggest moonlight. We also used a string of LED fairy lights to represent a road with streetlights.

For the smallest possible depth of field, everything was shot at f1.4. Even at ISO 320, in the daylight scenes it was necessary to add a 0.45 ND filter to bring the exposure down to f1.4.  We shot on a neutral picture profile, piping the images via HDMI to the Blackmagic Video Assist, where they were recorded in ProRes 422 HQ.

After a few years shooting on Blackmagics, FS7s and Alexas, the 5D’s colour saturation and contrast seemed very pronounced to me, but that really suited the toy-like nature of the map. And the tiny depth of field made everything look even smaller and cuter than it already was.

So, that’s a wrap on Above the Clouds finally and forever. Apparently.

See all my Above the Clouds posts here, or visit the official website..

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“Above the Clouds”: Summer 2017 Pick-ups