Inside a lens, amongst the various glass elements, is an ingenious mechanism which we call the iris. Just like your biological iris, it controls the amount of light passing through the pupil to form an image. I’ve written about the iris’s use to control exposure before, and its well-known side effect of controlling depth of field. But here are five things that aren’t so commonly known about irises.
1. f-stops and the entrance pupil
The f-number of a lens is the ratio of the focal length to the diameter of the aperture, but did you know that it isn’t the actual diameter of the aperture that’s used in this calculation? It’s the apparent diameter as viewed through the front of the lens. A lens might have a magnifying front element, causing the aperture to appear larger than its physical size, or a reducing one, causing it to appear smaller. Either way, it’s this apparent aperture – known as the entrance pupil – which is used to find the f-number.
2. No-parallax point
The no-parallax point of a lens is located at its entrance pupil. Sometimes called the nodal point, although that’s technically something different, this is the point around which the camera must pan and tilt if you want to eliminate all parallax. This is important for forced perspective work, for panoramas stitched together from multiple shots, and other types of VFX.
If you need to check your focal distance with a tape measure, many cameras have a handy Phi symbol on the side indicating where the sensor plane is located so that you can measure from that point. But technically you should be measuring to the entrance pupil. The sensor plane marker is just a convenient shortcut because the entrance pupil is in a different place for every lens and changes when the lens is refocused or zoomed. In most cases the depth of field is large enough for the shortcut to give perfectly acceptable results, however.
4. Bokeh shape
The shape of the entrance pupil determines the shape of the image’s bokeh (out of focus areas), most noticeable in small highlights such as background fairy lights. The pupil’s shape is determined both by the number of iris blades and the shape of their edges. The edges are often curved to approximate a circle when the iris is wide open, but form more of a polygon when stopped down. For example, a Cooke S4 produces octagonal bokeh at most aperture settings, indicating eight iris blades. Incidentally, an anamorphic lens has a roughly circular aperture like any other lens, but the entrance pupil (and hence the bokeh) is typically oval because of the anamorphosing effect of the front elements.
5. Diffraction spikes
When the edge of an iris blade is straight or roughly straight, it spreads out the light in a perpendicular direction, creating a diffraction spike. The result is a star pattern around bright lights, typically most visible at high f-stops. Every blade produces a pair of spikes in opposite directions, so the number of points in the star is equal to twice the number of iris blades – as long as that number is odd. If the number of blades is even, diffraction spikes from opposite sides of the iris overlap, so the number of apparent spikes is the same as the number of blades, as in the eight-pointed Cooke diffraction pictured above right.
When DSLR video exploded onto the indie filmmaking scene a decade ago, film festivals were soon awash with shorts with ultra-blurry backgrounds. Now that we have some distance from that first novelty of large-sensor cinematography we can think more intelligently about how depth of field – be it shallow or deep – is best used to help tell our stories.
First, let’s recap the basics. Depth of field is the distance between the nearest and farthest points from camera that are in focus. The smaller the depth of field, the less the subject has to move before they go out of focus, and the blurrier any background and foreground objects appear. On the other hand, a very large depth of field may make everything from the foreground to infinity acceptably sharp.
Depth of field is affected by four things: sensor (or film) size, focal length (i.e. lens length), focal distance, and aperture. In the days of tiny Mini-DV sensors, I was often asked by a director to zoom in (increase the focal length) to decrease the depth of field, but sometimes that was counter-productive because it meant moving the camera physically further away, thus increasing the focal distance, thus increasing the depth of field.
It was the large 35mm sensors of DSLRs, compared with the smaller 1/3” or 2/3” chips of traditional video cameras, that made them so popular with filmmakers. Suddenly the shallow depth of field seen in a Super-35 movie could be achieved on a micro-budget. It is worth noting for the purists, however, that a larger sensor technically makes for a deeper depth of field. The shallower depth of field associated with larger sensors is actually a product of the longer lenses required to obtain the same field of view.
Once a camera is selected and filming is underway, aperture is the main tool that DPs tend to use to control depth of field. A small aperture (large f- or T-number) gives a large depth of field; a large aperture (small f- or T-number) gives a narrow depth of field. What all those early DSLR filmmakers, high on bokeh, failed to notice is that aperture is, and always has been, a creative choice. Plenty of directors and DPs throughout the history of cinema have chosen deep focus when they felt it was the best way of telling their particular story.
One of the most famous deep-focus films is 1941’s Citizen Kane, frequently voted the greatest movie ever made. First-time director Orson Welles came from a theatre background, and instructed DP Gregg Toland to keep everything in focus so that the audience could choose what to look at just as they could in a theatre. “What if they don’t look at what they’re supposed to look at?” Welles was apparently asked. “If that happens, I would be a very bad director,” was his reply.
Stanley Kubrick was also fond of crisp backgrounds. The infamous f/0.7 NASA lenses used for the candlelight scenes in Barry Lyndon were a rare and extreme exception borne of low-light necessity. A typical Kubrick shot has a formal, symmetrical composition with a single-point perspective and everything in focus right into the distance. Take the barracks in Full Metal Jacket, for example, where the background soldiers are just as sharp as the foreground ones. Like Welles, Kubrick’s reasons may have lain in a desire to emulate traditional art-forms, in this case paintings, where nothing is ever blurry.
The Indiana Jones trilogy was shot at a surprisingly slow stop by the late, great Douglas Slocombe. “I prefer to work in the aperture range of T14-T14.5 when I am shooting an anamorphic film like Raiders,” he said at the time. “The feeling of depth contributed to the look.” Janusz Kamiński continued that deep-focus look, shooting at T8-T11 when he inherited the franchise for Kingdom of the Crystal Skull.
At the other end of the aperture scale, the current Hulu series The Handmaid’s Tale makes great creative use of a shallow depth of field, creating a private world for the oppressed protagonist which works in tandem with voiceovers to put the viewer inside her head, the only place where she is free.
A director called James Reynolds had a similar idea in mind when I shot his short film, Exile Incessant. He wanted to photograph closed-minded characters with shallow focus, and show the more tolerant characters in deep focus, symbolising their openness and connection with the world. (Unfortunately the tiny lighting budget made deep focus impossible, so we instead achieved the symbolism by varying the harshness of the lighting.)
One production where I did vary the depth of field was Ren: The Girl with the Mark, where I chose f/4 as my standard working stop, but reduced it to as little as f/1.4 when the lead character was bonding with the mysterious spirit inside her. It was the same principle again of separating the subject from the world around her.
Depth of field is a fantastic creative tool, and one which we are lucky to have so much control over with today’s cameras. But it will always be most effective when it’s used expressively, not just aesthetically.
Ever since digital cinematography became the norm, DPs have sought to counter the format’s perfection with characterful vintage lenses. Having just completed a feature film shoot, Hamlet, on Cooke Panchros and a Cooke 10:1 Varotal, I’m over the moon with the beautiful, creamy, organic look they brought to the production. However, I can’t deny that they have some disadvantages over modern glass which you should take into consideration before choosing the vintage approach.
Vintage lenses simply aren’t as sharp as their modern counterparts, particularly at the edges of frame and particularly when the iris is wide open. On Hamlet I deliberately shot with the Panchros wide open to soften the image, rather than adding a diffusion filter like I’ve often done in the past, but that look is not for everyone, and it does make things a little harder for your focus puller. Be sure to test the sharpness and view the results on a large screen before committing.
Breathe is the phenomenon whereby a lens appears to zoom slightly in or out when the focus is pulled. The Cooke Varotal is especially prone to this. As a result, my focus puller Aristide Russo had to be very gentle with his pulls otherwise the breathing was distracting.
Many DPs love lens flares, and beautiful, natural flares were one of the reasons I picked the vintage Cooke glass. But look out for veiling flare – a milkiness and lift in the shadows affecting the whole frame. I noticed this a lot when shooting under the practical fluorescents in Hamlet‘s stage set, especially with handheld shots where the veiling would appear and disappear depending on the camera’s angle to the lights. I decided to embrace it and make it part of the film’s look, but if maintaining high contrast at all times is important to you, lenses without modern coatings may not be the right choice.
Check for dark patches in the corners of your image. The Varotal I used vignetted at certain parts of the zoom range and not at others, so the dark corners would appear and disappear during a zoom. Although not ideal, it isn’t noticeable most of the time. Besides, I figured that most colourists add vignettes to most shots anyway, so I was simply saving them a little time!
Older lenses are, quite naturally, less reliable. Even if they have been rehoused, like our Cooke “Century” Panchros had been in 2000, you may find that the iris and/or focus sticks sometimes. Our 25mm started to play up halfway through our shoot, forcing Aris to use the rosettes to support the matte box, otherwise the motor wasn’t powerful enough to turn the focus ring. This possibility was flagged for me during testing when we had a similar issue with the 50mm. Even if all your lenses seem to be fine during prep, know that a vintage lens could start misbehaving at any time, and your rental house may not have another on the shelf to replace it with.
Don’t expect a set of vintage primes to all have the same maximum aperture or the same external configuration. The iris ring might be buried in the matte box, the matte box might not fit on at all, or it may be impossible to engage both iris and focus motors at the same time.
All this sounds quite negative, but the flares, softness, breathing and vignettes can be absolutely beautiful. Be aware of the downsides of using vintage glass, absolutely, but if they suit your story then embrace the flaws and get ready to be blown away by your dailies.
In case you missed them the first time, I’ll leave you with some highlights from my Hamlet lens tests.
In the first part of this series, I explained the concepts of f-stops and T-stops, and looked at how aperture can be used to control exposure. We saw that changing the aperture causes side effects, most noticeably altering the depth of field.
How can we set the correct exposure without compromising our depth of field? Well, as we’ll see later in this series, we can adjust the shutter angle and/or ISO, but both of those have their own side effects. More commonly a DP will use neutral density (ND) filters to control the amount of light reaching the lens. These filters get their name from the fact that they block all wavelengths of light equally, so they darken the image without affecting the colour.
When to use an ND Filter
Let’s look at an example. Imagine that I want to shoot at T4; this aperture gives a nice depth of field, on the shallow side but not excessively so. My subject is very close to a bright window and my incident light meter is giving me a reading of f/11. (Although I’m aiming for a T-stop rather an f-stop, I can still use the f-number my meter gives me; in fact if my lens were marked in f-stops then my exposure would be slightly off because the meter does not know the transmission efficiency of my lens.) Let’s remind ourselves of the f-stop/T-stop series before we go any further:
1 1.4 2 2.8 4 5.6 8 11 16 22 32
By looking at this series, which can be found printed on any lens barrel or permanently displayed on a light meter’s screen, I can see that f/11 (or T11) is three stops down from f/4 (or T4) – because 11 is three numbers to the right of 4 in the series. To achieve correct exposure at T4 I’ll need to cut three stops of light. I can often be seen on set counting the stops like this on my light meter or on my fingers. It is of course possible to work it out mathematically or with an app, but that’s not usually necessary. You quickly memorise the series of stops with practice.
What Strength of filter to choose
Some ND filters are marked in stops, so I could simply select a 3-stop ND and slide it into my matte box or screw it onto my lens. Other times – the built-in ND filters on the Sony FS7, for example – they’re defined by the fraction of light they let through. So the FS7’s 1/4 ND cuts two stops; the first stop halves the light – as we saw in part of one of this series – and the second stop halves it again, leaving us a quarter of the original amount. The 1/16 setting cuts four stops.
However, most commonly, ND filters are labelled in optical density. A popular range of ND filters amongst professional cinematographers are those made by Tiffen, and a typical set might be labelled as follows:
.3 .6 .9 1.2
That’s the optical density, a property defined as the natural logarithm of the ratio of the quantity of light entering the filter to the quantity of light exiting it on the other side. A .3 ND reduces the light by half because 10 raised to the power of -0.3 is about 0.5, and reducing light by half, as we’ve previously established, means dropping one stop.
If that maths is a bit much for you, don’t worry. All you really need to do is multiply the number of stops you want to cut by 0.3 to find the filter you need. So, going back to my example with the bright window, to get from T11 to T4, i.e. to cut three stops, I’ll pick the .9 ND.
It’s far from intuitive at first, but once you get your head around it, and memorise the f-stops, it’s not too difficult. Trust me!
Here are a couple more examples:
Light meter reads f/8 and you want to shoot at T5.6. That’s a one stop difference. (5.6 and 8 are right next to each other in the stop series, as you’ll see if you scroll back to the top.) 1 x 0.3 = 0.3 so you should use the .3 ND.
Light meter reads f/22 and you want to shoot at T2.8. That’s a six stop difference (scroll back up and count them), and 6 x 0.3 = 1.8, so you need a 1.8 ND filter. If you don’t have one, you need to stack two NDs in your matte box that add up to 1.8, e.g. a 1.2 and a .6.
Variations on a Theme
Variable ND filters are also available. These consist of two polarising filters which can be rotated against each other to progressively lighten or darken the image. They’re great for shooting guerilla-style with a small crew. You can set your iris where you want it for depth of field, then expose the image by eye simply by turning the filter. On the down side, they’re hard to use with a light meter because there is often little correspondence between the markings on the filter and stops. They can also have a subtle adverse effect on skin tones, draining a person’s apparent vitality, as some of the light which reflects off human skin is polarised.
Another issue to look out for with ND filters is infra-red (IR). Some filters cut only the visible wavelengths of light, allowing IR to pass through. Some digital sensors will interpret this IR as visible red, resulting in an image with a red colour cast which can be hard to grade out because different materials will be affected to different degrees. Special IR ND filters are available to eliminate this problem.
These caveats aside, ND filters are the best way to adjust exposure (downwards at least) without affecting the image in any other way.
In the next part of this series I’ll look at shutter angles, what they mean, how they affect exposure and what the side effects are.
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Lately, having run out of interesting series, I’ve found myself watching a lot of nineties blockbusters: Outbreak, Twister, Dante’s Peak, Backdraft, Daylight. Whilst eighties movies were the background to my childhood, and will always have a place in my heart, it was the cinema of the nineties that I was immersed in as I began my own amateur filmmaking. So, looking back on those movies now, while certain clichés stand out like sore thumbs, they still feel to me like solid examples of how to make a summer crowd-pleaser.
Let’s get those clichés out of the way first. The lead character always has a failed marriage. There’s usually an opening scene in which they witness the death of a spouse or close relative, before the legend “X years later” fades up. The dog will be saved, but the crotchety elderly character will die nobly. Buildings instantly explode towards camera when touched by lava, hurricanes, floods or fires. A stubborn senior authority figure will refuse to listen to the disgraced lead character who will ultimately be proven correct, to no-one’s surprise.
There’s an intensity to nineties action scenes, born of the largely practical approach to creating them. The decade was punctuated by historic advances in digital effects: the liquid metal T-1000 in Terminator 2 (1991), digital dinosaurs in Jurassic Park(1993), motion-captured passengers aboard the miniature Titanic (1997), Bullet Time in The Matrix (1999). Yet these techniques remained expensive and time-consuming, and could not match traditional methods of creating explosions, floods, fire or debris. The result was that the characters in jeopardy were generally surrounded by real set-pieces and practical effects, a far more nerve-wracking experience for the viewer than today, when we can tell that our heroes are merely imagining their peril on a green-screen stage.
One thing I was looking out for during these movie meanders down memory lane was lens selection. A few weeks back, a director friend had asked me to suggest examples of films that preferred long lenses. He had mentioned that such lenses were more in vogue in the nineties, which I’d never thought about before.
As soon as I started to consider it, I realised how right my friend was. And how much that long-lens looked had influenced me. When I started out making films, I was working with the tiny sensors of Mini-DV cameras. I would often try to make my shots look more cinematic by shooting on the long end of the zoom. This was partly to reduce the depth of field, but also because I instinctively felt that the compressed perspective was more in keeping with what I saw at the cinema.
I remember being surprised by something that James Cameron said in his commentary on the Aliens DVD:
I went to school on Ridley [Scott]’s style of photography, which was actually quite a bit different from mine, because he used a lot of long lenses, much more so than I was used to working with.
I had assumed that Cameron used long lenses too, because I felt his films looked incredibly cinematic, and because I was so sure that cinematic meant telephoto. I’ve discussed in the past what I think people tend to mean by the term “cinematic”, and there’s hardly a definitive answer, but I’m now sure that lens length has little to do with it.
And yet… are those nineties films influencing me still? I have to confess, I struggle with short lenses to this day. I find it hard to make wide-angle shots look as good. On Above the Clouds, to take just one example, I frequently found that I preferred the wide shots on a 32mm than a 24mm. Director Leon Chambers agreed; perhaps those same films influenced him?
A deleted scene from Ren: The Girl with the Mark ends with some great close-ups shot on my old Sigma 105mm still lens, complete with the slight wobble of wind buffeting the camera, which to my mind only adds to the cinematic look! On a more recent project, War of the Worlds: The Attack, I definitely got a kick from scenes where we shot the heroes walking towards us down the middle of the street on a 135mm.
Apart from the nice bokeh, what does a long lens do for an image? I’ve already mentioned that it compresses perspective, and because this is such a different look to human vision, it arguably provides a pleasing unreality. You could describe it as doing for the image spatially what the flicker of 24fps (versus high frame rates) does for it temporally. Perhaps I shy away from short lenses because they look too much like real life, they’re too unforgiving, like many people find 48fps to be.
The compression applies to people’s faces too. Dustin Hoffman is not known for his small nose, yet it appears positively petite in the close-up below from Outbreak. While this look flatters many actors, others benefit from the rounding of their features caused by a shorter lens.
Perhaps the chief reason to be cautious of long lenses is that they necessitate placing the camera further from the action, and the viewer will sense this, if only on a subconscious level. A long lens, if misused, can rob a scene of intimacy, and if overused could even cause the viewer to disengage with the characters and story.
I’ll leave you with some examples of long-lens shots from the nineties classics I mentioned at the start of this post. Make no mistake, these films employed shorter lenses too, but it certainly looks to me like they used longer lenses on average than contemporary movies.
Each month I get a digital copy of American Cinematographer to my inbox, filled with illuminating (pun intended) articles about the lighting and lensing of the latest theatrical releases. As a rule of thumb, I only read the articles if I’ve seen the films. Trouble is, I don’t go to the cinema much any more… even before Coronavirus put a stop to all that anyway.
Why? TV is better, simple as that. Better writing, better cinematography, better value for money. (Note: I include streaming services like Netflix and Amazon under the umbrella of “TV” here.) But whereas I can turn to AC to discover the why and how of the cinematography of a movie, there is no equivalent for long-form content. I would love to see a magazine dedicated to the beautiful cinematography of streaming shows, but until then I’ll try to plug the gap myself.
I’d like to start with a look at the increasing use of anamorphic lenses for the small screen. Let’s look at a few examples and try to discover what anamorphic imaging adds to a project.
Lenses with an anamorphic element squeeze the image horizontally, allowing a wider field of view to be captured. The images are restored to their correct proportions in postproduction, but depth of field, bokeh (out of focus areas), barrel distortion and lens flare all retain different characteristics to those obtained with traditional spherical lenses.
The Cinematic look
The venerable Doctor Who, which started off shooting on 405-line black-and-white videotape more than half a century ago, has employed Arri Alexas and Cooke Anamorphic/i glass since the introduction of Jodie Whittaker’s 13th Doctor. “[Director Jamie Childs] suggested we shoot on anamorphic lenses to give it a more filmic look,” says DP Denis Crossan. “You get really nice background falloff and out of focus ellipses on light sources.”
While most viewers will not be able to identify these visual characteristics specifically, they will certainly be aware of a more cinematic feel to the show overall. This is because we associate anamorphic images – even if we do not consciously know them as such – with the biggest of Hollywood blockbusters, everything from Die Hard to Star Trek Beyond.
It’s not just the BBC who are embracing anamorphic. DP Ollie Downey contrasted spherical glass with vintage anamorphics to deliberate effect in “The Commuter”, an episode of the Channel 4/Amazon sci-fi anthology series Electric Dreams.
The story revolves around Ed (Timothy Spall) whose mundane but difficult life turns upside down when he discovers Macon Heights, a town that seems to exist in an alternate reality. “Tim Spall’s character is torn between his real life and the fantastical world of Macon Heights,” Downey explains on his Instagram feed. “We shot Crystal Express Anamorphics for his regular life, and Zeiss Super Speed Mk IIs for Macon Heights.”
The anamorphic process was invented as a way to get a bigger image from the same area of 35mm negative, but in today’s world of ultra-high-resolution digital sensors there is no technical need for anamorphics, only an aesthetic one. In fact, they can actually complicate the process, as Downey notes: “We had to shoot 8K on the Red to be able to punch in to our Crystal Express to extract 16:9 and still deliver 4K to Amazon.”
Evoking a period
Back at the BBC, last year’s John le Carré adaptation The Little Drummer Girl uses anamorphic imaging to cement its late 1970s setting. The mini-series revolves around Charmian, an actress who is recruited by Israeli intelligence via the mysterious agent Becker. The truth is distorted throughout, just as the wide anamorphic lenses distort every straight line into a curve.
Reviewing the show for The Independent, Ed Cumming notes that director Park Chan-wook “does not aim to be invisible but to remind you constantly that what you are seeing is a creation. Take the scene at a beachside taverna in Greece, where Charmian and Becker start talking properly to each other. The camera stays still, the focus snaps between him and her.” Such focus pulls are more noticeable in anamorphic because the subject stretches vertically as it defocuses.
The Little Drummer Girl is slavish in its recreation of the period, in camera style as well as production design. Zooms are used frequently, their two-dimensional motion intricately choreographed with the actors who step in and out of multiple planes in the image. Such shots were common in the 70s, but have since fallen very much out of fashion. When once they would have passed unnoticed, a standard part of film grammar, they now draw attention.
Chilling Adventures of Sabrina, a Netflix Original, also draws attention with its optics. Charting the trials and tribulations of a teenaged witch, the show uses different makes of lenses to differentiate two worlds, just like “The Commuter”.
According to DP David Lazenberg’s website, he mixed modern Panavision G series anamorphics with “Ultragolds”. Information on the latter is hard to find, but they may be related to the Isco Ultra Star adapters which some micro-budget filmmakers have adopted as a cheap way of shooting anamorphic.
The clean, sharp G series glass is used to portray Sabrina’s ordinary life as a small-town teenager, while the Ultragolds appear to be used for any scenes involving witchcraft and magic. Such scenes display extreme blur and distortion at the edges of the frame, making characters squeeze and stretch as the camera pans over them.
Unlike the anamorphic characteristics of Doctor Who or “The Commuter”, which are subtle, adding to the stories on a subconscious level, the distortion in Sabrina is extreme enough to be widely noticed by its audience. “Numerous posts on Reddit speak highly of Chilling Adventures of Sabrina’s content and cinematography,” reports Andy Walker, editor of memeburn.com, “but a majority have a collective disdain for the unfocused effect.”
“I hate that blurry s*** on the side of the screen in Sabrina,” is the more blunt appraisal of Twitter user @titanstowerr. Personally I find the effect daring and beautiful, but it certainly distracted me just as it has distracted others, which forces me to wonder if it takes away more from the story than it adds.
And that’s what it all comes down to in the end: are the technical characteristics of the lens facilitating or enhancing the storytelling? DPs today, in both cinema and long-form series, have tremendous freedom to use glass to enhance the viewers’ experience. Yes, that freedom will sometimes result in experiments that alienate some viewers, but overall it can only be a good thing for the expressiveness of the art form.
Today I’m investigating the so-called normal (a.k.a. standard) lens, finding out exactly what it is, the history behind it, and how it’s relevant to contemporary cinematographers.
The Normal lens in still photography
A normal lens is one whose focal length is equal to the measurement across the diagonal of the recorded image. This gives an angle of view of about 53°, which is roughly equivalent to that of the human eye, at least the angle within which the eye can see detail. If a photo taken with a normal lens is printed and held up in front of the real scene, with the distance from the observer to the print being equal to the diagonal of the print, then objects in the photo will look exactly the same size as the real objects.
Lenses with a shorter focal length than the normal are known as wide-angle. Lenses with a greater focal length than the normal are considered to be long lenses. (Sometimes you will hear the term telephoto used interchangeably with long lens, but a telephoto lens is technically one which has a focal length greater than its physical length.)
A still 35mm negative is 43.3mm across the diagonal, but this got rounded up quite a bit — by Leica inventor Oskar Barnack — so that 50mm is widely considered to be the normal lens in the photography world. Indeed, some photographers rarely stray from the 50mm. For some this is simply because of its convenience; it is the easiest length of lens to manufacture, and therefore the cheapest and lightest. Because it’s neither too short nor too long, all types of compositions can be achieved with it. Other photographers are more dogmatic, considering a normal lens the only authentic way to capture an image, believing that any other length falsifies or distorts perspective.
The normal lens in cinematography
SMPTE (the Society of Motion Picture and Television Engineers), or indeed SMPE as it was back then, decided almost a century ago that a normal lens for motion pictures should be one with a focal length equal to twice the image diagonal. They reasoned that this would give a natural field of view to a cinema-goer sitting in the middle of the auditorium, halfway between screen and projector (the latter conventionally fitted with a lens twice the length of the camera’s normal lens).
A Super-35 digital cinema sensor – in common with 35mm motion picture film – has a diagonal of about 28mm. According to SMPE, this gives us a normal focal length of 56mm. Acclaimed twentieth century directors like Hitchcock, Robert Bresson and Yasujiro Ozu were proponents of roughly this focal length, 50mm to be more precise, believing it to have the most natural field of view.
Of course, the 1920s SMPE committee, living in a world where films were only screened in cinemas, could never have predicted the myriad devices on which movies are watched today. Right now I’m viewing my computer monitor from a distance about equal to the diagonal of the screen, but to hold my phone at the distance of its diagonal would make it uncomfortably close to my face. Large movie screens are still closer to most of the audience than their diagonal measurement, just as they were in the twenties, but smaller multiplex screens may be further away than their diagonals, and TV screens vary wildly in size and viewing distance.
The new normal
To land in the middle of the various viewing distances common today, I would argue that filmmakers should revert to the photography standard of a normal focal length equal to the diagonal, so 28mm for a Super-35 sensor.
According to Noam Kroll, “Spielberg, Scorsese, Orson Wells, Malick, and many other A-list directors have cited the 28mm lens as one of their most frequently used and in some cases a favorite [sic]”.
I have certainly found lenses around that length to be the most useful on set.A 32mm is often my first choice for handheld, Steadicam, or anything approaching a POV. It’s great for wides because it compresses things a little and crops out unnecessary information while still taking plenty of the scene in. It’s also good for mids and medium close-ups, making the viewer feel involved in the conversation.
When I had to commit to a single prime lens to seal up in a splash housing for a critical ocean scene in The Little Mermaid, I quickly chose a 32mm, knowing that I could get wides and tights just by repositioning myself.
I’ve found a 32mm useful in situations where coverage was limited. Many scenes in Above the Clouds were captured as a simple shot-reverse: both mids, both on the 32mm. This was done partly to save time, partly because most of the sets were cramped, and partly because it was a very effective way to get close to the characters without losing the body language, which was essential for the comedy. We basically combined the virtues of wides and close-ups into a single shot size!
In addition to the normal lens’ own virtues, I believe that it serves as a useful marker post between wide lenses and long lenses. In the same way that an editor should have a reason to cut, in a perfect world a cinematographer should have a reason to deviate from the normal lens. Choose a lens shorter than the normal and you are deliberately choosing to expand the space, to make things grander, to enhance perspective and push planes apart. Select a lens longer than the normal and you’re opting for portraiture, compression, stylisation, maybe even claustrophobia. Thinking about all this consciously and consistently throughout a production can add immeasurably to the impact of the story.
Exposing the image correctly is one of the most important parts of a cinematographer’s job. Choosing the T-stop can be a complex technical and creative decision, but fortunately there are many ways we can measure light to inform that decision.
First, let’s remind ourselves of the journey light makes: photons are emitted from a source, they strike a surface which absorbs some and reflects others – creating the impressions of colour and shade; then if the reflected light reaches an eye or camera lens it forms an image. We’ll look at the various ways of measuring light in the order the measurements occur along this light path, which is also roughly the order in which these measurements are typically used by a director of photography.
1. Photometrics data
You can use data supplied by the lamp manufacturer to calculate the exposure it will provide, which is very useful in preproduction when deciding what size of lamps you need to hire. There are apps for this, such as the Arri Photometrics App, which allows you to choose one of their fixtures, specify its spot/flood setting and distance from the subject, and then tells you the resulting light level in lux or foot-candles. An exposure table or exposure calculation app will translate that number into a T-stop at any given ISO and shutter interval.
2. Incident meter
Some believe that light meters are unnecessary in today’s digital landscape, but I disagree. Most of the methods listed below require the camera, but the camera may not always be handy – on a location recce, for example. Or during production, it would be inconvenient to interrupt the ACs while they’re rigging the camera onto a crane or Steadicam. This is when having a light meter on your belt becomes very useful.
An incident meter is designed to measure the amount of light reaching the subject. It is recognisable by its white dome, which diffuses and averages the light striking its sensor. Typically it is used to measure the key, fill and backlight levels falling on the talent. Once you have input your ISO and shutter interval, you hold the incident meter next to the actor’s face (or ask them to step aside!) and point it at each source in turn, shading the dome from the other sources with your free hand. You can then decide if you’re happy with the contrast ratios between the sources, and set your lens to the T-stop indicated by the key-light reading, to ensure correct exposure of the subject’s face.
3. Spot meter (a.k.a. reflectance meter)
Now we move along the light path and consider light after it has been reflected off the subject. This is what a spot meter measures. It has a viewfinder with which you target the area you want to read, and it is capable of metering things that would be impractical or impossible to measure with an incident meter. If you had a bright hillside in the background of your shot, you would need to drive over to that hill and climb it to measure the incident light; with a spot meter you would simply stand at the camera position and point it in the right direction. A spot meter can also be used to measure light sources themselves: the sky, a practical lamp, a flame and so on.
But there are disadvantages too. If you spot meter a Caucasian face, you will get a stop that results in underexposure, because a Caucasian face reflects quite a lot of light. Conversely, if you spot meter an African face, you will get a stop that results in overexposure, because an African face reflects relatively little light. For this reason a spot meter is most commonly used to check whether areas of the frame other than the subject – a patch of sunlight in the background, for example – will blow out.
Your smartphone can be turned into a spot meter with a suitable app, such as Cine Meter II, though you will need to configure it using a traditional meter and a grey card. With the addition of a Luxiball attachment for your phone’s camera, it can also become an incident meter.
The remaining three methods of judging exposure which I will cover all use the camera’s sensor itself to measure the light. Therefore they take into account any filters you’re using as well transmission loss within the lens (which can be an issue when shooting on stills glass, where the marked f-stops don’t factor in transmission loss).
4. Monitors and viewfinders
In the world of digital image capture, it can be argued that the simplest and best way to judge exposure is to just observe the picture on the monitor. The problem is, not all screens are equal. Cheap monitors can misrepresent the image in all kinds of ways, and even a high-end OLED can deceive you, displaying shadows blacker than any cinema or home entertainment system will ever match. There are only really two scenarios in which you can reliably judge exposure from the image itself: if you’ve owned a camera for a while and you’ve become very familiar with how the images in the viewfinder relate to the finished product; or if the monitor has been properly calibrated by a DIT (Digital Imaging Technician) and the screen is shielded from light.
Most cameras and monitors have built-in tools which graphically represent the luminance of the image in a much more accurate way, and we’ll look at those next. Beware that if you’re monitoring a log or RAW image in Rec.709, these tools will usually take their data from the Rec.709 image.
5. Waveforms and histograms
These are graphs which show the prevalence of different tones within the frame. Histograms are the simplest and most common. In a histogram, the horizontal axis represents luminance and the vertical axis shows the number of pixels which have that luminance. It makes it easy to see at a glance whether you’re capturing the greatest possible amount of detail, making best use of the dynamic range. A “properly” exposed image, with a full range of tones, should show an even distribution across the width of the graph, with nothing hitting the two sides, which would indicate clipped shadows and highlights. A night exterior would have a histogram crowded towards the left (darker) side, whereas a bright, low contrast scene would be crowded on the right.
A waveform plots luminance on the vertical axis, with the horizontal axis matching the horizontal position of those luminance values within the frame. The density of the plotting reveals the prevalence of the values. A waveform that was dense in the bottom left, for example, would indicate a lot of dark tones on the lefthand side of frame. Since the vertical (luminance) axis represents IRE (Institute of Radio Engineers) values, waveforms are ideal when you need to expose to a given IRE, for example when calibrating a system by shooting a grey card. Another common example would be a visual effects supervisor requesting that a green screen be lit to 50 IRE.
6. Zebras and false colours
Almost all cameras have zebras, a setting which superimposes diagonal stripes on parts of the image which are over a certain IRE, or within a certain range of IREs. By digging into the menus you can find and adjust what those IRE levels are. Typically zebras are used to flag up highlights which are clipping (theoretically 100 IRE), or close to clipping.
Exposing an image correctly is not just about controlling highlight clipping however, it’s about balancing the whole range of tones – which brings us to false colours. A false colour overlay looks a little like a weather forecaster’s temperature map, with a code of colours assigned to various luminance values. Clipped highlights are typically red, while bright areas still retaining detail (known as the “knee” or “shoulder”) are yellow. Middle grey is often represented by green, while pink indicates the ideal level for caucasian skin tones (usually around 55 IRE). At the bottom end of the scale, blue represents the “toe” – the darkest area that still has detail – while purple is underexposed. The advantage of zebras and false colours over waveforms and histograms is that the former two show you exactly where the problem areas are in the frame.
I hope this article has given you a useful overview of the tools available for judging exposure. Some DPs have a single tool they rely on at all times, but many will use all of these methods at one time or another to produce an image that balances maximising detail with creative intent. I’ll leave you with a quote from the late, great Douglas Slocombe, BSC who ultimately used none of the above six methods!
I used to use a light meter – I used one for years. Through the years I found that, as schedules got tighter and tighter, I had less and less time to light a set. I found myself not checking the meter until I had finished the set and decided on the proper stop. It would usually say exactly what I thought it should. If it didn’t, I wouldn’t believe it, or I would hold it in such a way as to make it say my stop. After a time I decided this was ridiculous and stopped using it entirely. The “Raiders” pictures were all shot without a meter. I just got used to using my eyes.
Anamorphic cinematography, first dabbled with in the 1920s, was popularised by Twentieth Century Fox in the fifties as CinemaScope. Television was growing in popularity and the studios were inventing gimmicks left, right and centre to encourage audiences back into cinemas. Fox’s idea was to immerse viewers in an image far wider than they were used to, but with minimal modifications to existing 4-perf 35mm projectors. They developed a system of anamorphic lenses containing elements which compressed the image horizontally by a factor of two. By placing a corresponding anamorphosing lens onto existing projectors, the image was unsqueezed into an aspect ratio of 2.55:1, or later 2.39:1.
Since those early days of CinemaScope, anamorphic cinematography has become associated with the biggest Hollywood blockbusters. Its optical features – streak flares, oval bokeh and curved horizontal lines – have been seared into our collective consciousness, indelibly associated with high production values.
Again we were shooting on an Alexa XT Plus in log C ProRes 4444 XQ, this time in 4:3 mode, a resolution of 2048×1536. Since all of the lenses had a standard 2:1 anamorphosing ratio, the images unsqueezed to a super-wide 2.66:1 ratio. (This is because the lenses were designed to be used on 35mm film with space left to one side for the optical soundtrack.) You can see the full width of this ratio in the first split-screen image in the video, at 2:08, and in the second image below, but otherwise I have horizontally cropped the footage to the standard 2.39:1 ratio.
We tested the following glass:
* CF = close focus
For consistency with the spherical lenses, we used lengths around 32mm, but in the anamorphic format this is a pretty wide lens, not a mid-range lens. We shot at T2.8, again for consistency, but I hear that many anamorphics don’t perform well wider than T4.
We were only able to test what Arri Rental happened to have on the shelves that day. The biggest and presumably most expensive was the Hawk V-series. Next in size and weight was the Cooke Xtal – pronounced “crystal” – a 1970s lens based on the much-loved Speed Panchros. The smallest and lightest, was the Kowa Mirrorscope, with a list price of £1,200 per week for a set of four. (Sorry, I couldn’t find any pricing info for the others online.) Note that there isn’t really a 30mm Mirrorscope; to get this length you put a wide angle adapter on the 40mm. As this extra element decreases the optical performance, we tested it with and without, hence the two lengths.
Here’s the video…
Click on the image to see it at full quality.
To my eye, the Hawk has a fairly rich, warm skin tone, while the Cooke – as with the spherical S4 tested last week – seems a little grey and flat. The Kowa is inexplicably brighter than the other two lenses, which makes it hard to compare, but perhaps it’s a little cooler in tone?
Anamorphic lenses have what is known as a “curved field of focus” that works similarly to the curved movie screens in some large Cinerama theatres. This is one reason that one needs to expose these lenses at a deeper stop. If one doesn’t, the curved field will not be covered by depth of field and either the edges or centre of the frame will be soft.
One day I’d like to re-test these lenses at a lower stop, T4 or T5.6, where they will all undoubtedly perform much better. But in this T2.8 test, on Bex’s face in the centre of frame, the Hawk V and the Kowa Mirrorscope 40mm – both almost a full stop from their maximum apertures – are clearly the sharpest of the bunch. The Cooke Xtal, which is wide open, is unsurprisingly softer. The 30mm adapter on the Mirrorscope completely destroys the image, not only making it very soft but also introducing colour aberration.
Now let’s look at the checkerboard at the side of frame and see if we can spot any differences in sharpness there…
It seems to me that the Kowa, both with and without the adapter, has a greater difference in sharpness between the centre and edges of frame than the the Hawk and Cooke. With the latter two lenses, the checkerboard is reasonably sharp, at least on the lefthand side, with some ghosting/blur visible towards the righthand side. The same thing can be observed on the chart in the flare tests at the end of the video.
Breathing & Bokeh
All of these lenses have a noticeable degree of breathe, which I suppose is to be expected from anamorphics. The Hawk V has roughly oval bokeh, the Cooke’s is more circular, while the Mirrorscope has interesting D-shaped bokeh.
The Hawk V doesn’t flare much at all, which is apparently due to the anamorphic element being in the middle of the lens, rather than at the front. The Kowa has a nice streak and glow around the light source, with a funky purple artefact on the opposite side of frame. But it’s the Cooke Xtal which provides the most classic lens flare, with a horizontal line across most of the frame and a partial star pattern around the source, despite the lens being wide open.
At the end of the video you can see how the flares develop on each lens as the light source moves horizontally across frame.
A bulging effect is very obvious on all of these lenses, due to the focal lengths being quite wide for anamorphic. Notice how at 40mm on the Kowa Mirrorscope this curvature of the image is significantly reduced.
It’s hard to compare the levels of distortion because none of the focal lengths are exactly the same, except for the Cooke Xtal and the Kowa Mirrorscope with the 30mm adapter on. The Cooke’s top right and bottom left corners appear to be stretched away from the centre relative to the other two corners. I suppose that strange and funky stuff like this is exactly why you choose vintage glass.
Interestingly, the Cooke’s image appears a little tighter than the Kowa’s, which combined with my inability to find any evidence online of the existence of a 30mm Xtal, leads me to suspect we may have been given a mislabelled 32mm.
When we got to the end of our spherical tests and started putting the anamorphics on, I was shocked by the drop in sharpness. But as noted earlier, this is because anamorphics really need to be used with a smaller aperture than the T2.8 I often shoot at. If I learnt nothing else from this test, I learnt that anamorphic needs more light!
I would love to put the Cooke Xtal’s lovely flares and general vintage look to good use on a period movie one day. The Hawk V would be a good choice if I wanted the anamorphic look with warm, dynamic skin tones. The Kowa system seemed a little cheap and cobbled-together, but could well be a good solution for anamorphic on a budget, as long as I stayed away from the 30mm adapter!
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.
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:
Arri/Zeiss Master Prime
Zeiss High Speed
(a.k.a. Superspeed Mk III)
Arri/Zeiss Ultra Prime
* CF = close focus
Here’s the video…
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.
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 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.
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 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.
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.