What I Learnt from DSLRs

RedShark News recently published an article called “The DSLR is now dead”, based on the fact that the Canon 1D X Mark III will be the last flagship DSLR from the company and that mirrorless cameras are now first choice for most photographers. This prompted me to reflect on some of the things I learnt when I bought my first (and only) DSLR.

It was 2011, and I documented some of the challenges my new Canon 600D created for me in this blog post. But what the DSLR did really well was to introduce me to a workflow very similar in many ways to the bigger productions I’m working on now. Previously I had shot everything on prosumer camcorders, so the following things were new to me with DSLRs and have been constant ever since.

 

Shallow Depth of Field

I had been used to everything being in focus, so not really thinking about my aperture setting, just turning the iris dial until the exposure looked right. My Canon 600D set me on a journey of understanding f-stops, and eventually choosing a target stop to shoot at for focus reasons and then using lighting or ND filters to achieve that stop.

 

Prime Lenses

My lenses

Although for several years I owned a Canon XL1-S, which had interchangeable lenses, I only ever owned a couple of zooms for it. As far as I’m aware, no prime lenses to fit the XL1-S’s proprietary mount were ever made, so prime lenses were completely new to me when I got my 600D. As with aperture, it forced me to think about what field of view and degree of perspective or compression I wanted, select the appropriate lens, and then place the camera accordingly, rather than lazily zooming to get the desired framing.

 

Dual-System Sound

It’s weird now to think that I used to be tethered to the sound recordist before I switched to DSLR shooting. At the time I was doing most of my own editing as well, so syncing the sound was a pain in the arse, but it was a valuable introduction to this industry-standard way of working. It’s also weird to think that clapperboards were optional for me before this.

 

Building a camera rig

All my cameras before the 600D had a built-in viewfinder, handgrip, shoulder mount (if the camera was large enough to need one) and lens (except the XL1-S), and there was no need to add an external battery plate or a follow-focus. The idea that a camera rig needed to be built, and that it could be customised to suit different operators and situations, was a novel one to me. I have to say that I still prefer cameras that have more things built in, like the Alexa Classic. A good part of the reason I rarely use Reds is because they don’t come with viewfinders. Why anyone ever thinks a viewfinder is an optional part of a camera is utterly beyond me. It’s an important point of stabilising contact for handheld work, and your face shields it completely from extraneous light, unlike a monitor.

 

Tapeless recording

The 600D was my first camera to record to memory cards rather than magnetic tape. It was certainly scary to have to wipe the cards during a shoot, being careful to back everything up a couple of times first. Data wrangling was a tricky thing to deal with on the kind of tiny-crewed productions I was usually doing back then, but of course now it’s completely normal. Just last week I shot my new cinematography course and had the fun of staying up until 2:30am after a long day of shooting, to make sure all the footage was safely ingested! More on that course soon.

What I Learnt from DSLRs

“The Little Mermaid”: A Tale of Two Cameras

As The Little Mermaid is leaving Netflix next week, I decided to go back to my production diary from 2016 and see if there were any more extracts that might be of interest. Tying in with my recent post about shooting with two cameras, here are a number of extracts demonstrating how we used our Alexa Plus XR (operated by me) and Alexa Studio XR (operated by Tim Gill). I definitely won’t say that we made the most effective and efficient use of two cameras the whole time, but I certainly learnt a lot about the pros and cons of having a B-cam.

 

Day 1

We start in a third floor bedroom… After we get the main coverage, we head out to the garden for the next scene, while the B-camera team steps in to pick up a couple of inserts.

As soon as we’re outside, the sun starts to dick around. Those clouds are scudding in and out faster than we can swap ND filters and fly in Ultrabounce to fill the shadows. Eventually we get the three-channel Preston (which only arrived this morning) hooked up so I can pull the iris remotely for our big jib shot. B-camera arrives and picks up alternate angles, and using the two cameras we’re able to wrap out the scenes by lunchtime.

Now we’re inside, on the first floor this time, in a beautiful little circular study. The electrical department have already set up the lamps, so it doesn’t take much tweaking to get us ready to go. Over the course of the afternoon we shoot out our scenes in the study, while B-camera gets various POVs out of windows and establishers of the house exterior. Although the G&E (grip and electric) crew are thinly stretched to support both camera crews, having that second camera is incredibly useful.

 

Day 2

This morning we’re in a church, shooting a montage scene in which Cam interviews a number of locals. We use two cameras to capture a locked-off wide of the interviewee (which can be jump-cut between characters) and a roaming CU simultaneously. Since Tim’s B-camera is doing the roaming shot, I spend the morning at the monitors, keeping an eye on both feeds…

 

Day 3

The forecast says cloudy all week, and we dearly want our exteriors at Lorene’s House to be sunny and beautiful. But actually the dark, overcast skies work in our favour when the AD has us spend the morning shooting a “sunset” exterior. Our 12K HMI, gelled with full CTS, has enough power to cut through the dim natural light and give the impression of a gentle sunset. Working with both cameras, we get a great tracking shot, a jib shot and some other coverage. Then we leave the B-camera team behind, under the direction of VFX supervisor Rich (for the above green-screen shot), while we move back inside to block and light other scenes…

 

Day 8

… We have planned our day to maximise our two cameras. We’ve only been getting about eight set-ups a day, and we knew that with the stunts and effects we have today we would be pushed to even get that many. So we planned six two-camera set-ups and an insert, and we stick closely to this plan. A-camera lives on the crane with the (Angenieux 19.5-94mm Optimo) zoom most of the day, getting the most out of the scale and height of the big top and the action, while B-camera – using the (Cooke S4/i) primes for a change – gets the closer shots. This leaves me free to look at the monitors, which is useful but often boring. (All the material from this day sadly hit the cutting room floor.)

 

Day 12

Our last day at the circus… For most of the day the B-camera is nearby shooting different stuff. This is great in principle, but in practice we tend to get in each others’ way, our lighting affecting their shots and vice versa.

 

Day 24

… After lunch we have a big fight scene to shoot, and the pace of work kicks up several gears. I light a small clearing so we can shoot 180 degrees with two cameras simultaneously. Some directions look better than others, but in an action scene no shot will be held for very long, so it’s not necessary to get every angle perfect.

Normally I open the Cooke S4s no wider than 2 and two thirds, as no lens performs at its best when wide open, but my resolve on this is slipping, and it’s really hard to get a decent amount of light through the dense trees at this location, so I go wide open (T2) for this sequence.

 

Day 25

Our last day on Tybee Island. We start with pick-ups in the woods for various scenes shot over the last few days, then move to the beach, a portion of which we’re cheating as a “river marsh” location. This is a night scene, so we have to go through the slow process of moving the condor (cherry-picker) around from the woods. This involves a police escort to get it across the highway…

Meanwhile B-camera are shooting a shot of a car driving along the road behind the beach. Since the G&E crew are all tied up, at (co-director) Chris Bouchard’s suggestion they use the location work-light and have to fiddle with the white balance to render it a reasonable colour on camera. More and more micro-budget cheats are being employed as the production goes on, and to most of the crew, who are used to big-budget stuff, it’s ridiculous. I don’t mind so much, but I feel bad for the B-camera team.

 

Day 26

We are back on the stage, in three different sets. I’ve lit them all before, but most of the lamps are gone and some require a new look because the time of day is different. Towards the end of the night we leap-frog from set to set, sending G&E and the B-camera ahead to set up while we’re still shooting. To my surprise it works. The sets are small enough that we have enough G&E crew to split up like that.

Top row: A-cam 1st AC Jonathan Klepfer, A-cam 2nd AC Kane Pearson, me, B-cam 1st AC Geran Daniels; bottom row: B-cam 2nd AC Matt Bradford Dixon, digital loader Alex Dubois, B-cam operator/2nd unit DP Tim Gill

For more extracts from my Little Mermaid diary, visit these links:

The Little Mermaid is currently available on Netflix in the UK – but hurry because it leaves on November 30th – and Showtime in the US.

“The Little Mermaid”: A Tale of Two Cameras

The Art and Science of White Balance

Mixed colour temperatures in “Annabel Lee”

Colour temperature starts with something mysterious called a “black body”, a theoretical object which absorbs all frequencies of electromagnetic radiation and emits it according to Planck’s Law. Put simply, Planck’s Law states that as the temperature of such a body increases, the light which it emits moves toward the blue end of the spectrum. (Remember from chemistry lessons how the tip of the blue flame was the hottest part of the Bunsen Burner?)

Colour temperature is measured in kelvins, a scale of temperature that begins at absolute zero (-273°C), the coldest temperature physically possible in the universe. To convert centigrade to kelvin, simply add 273.

Tungsten bulbs emit an orange light - dim them down and it gets even more orangey.The surface of the sun has a temperature of 5,778K (5,505°C), so it emits a relatively blue light. The filament of a tungsten studio lamp reaches roughly 3,200K (2,927°C), providing more of an orange light. Connect that fixture to a dimmer and bring it down to 50% intensity and you might get a colour temperature of 2,950K, even more orange.

Incandescent lamps and the sun’s surface follow Planck’s Law fairly closely, but not all light sources rely on thermal radiation, and so their colour output is not dependent on temperature alone. This leads us to the concept of “correlated colour temperature”.

Colour temperature chartThe correlated colour temperature of a source is the temperature which a black body would have to be at in order to emit the same colour of light as that source. For example, the earth’s atmosphere isn’t 7,100K hot, but the light from a clear sky is as blue as a Planckian body glowing at that temperature would be. Therefore a clear blue sky has a correlated colour temperature (CCT) of 7,100K.

LED and fluorescent lights can have their colour cast at least partly defined by CCT, though since CCT is one-dimensional, measuring only the amount of blue versus red, it may give us an incomplete picture. The amounts of green and magenta which LEDs and fluorescents emit varies too, and some parts of the spectrum might be missing altogether, but that’s a whole other can of worms.

The human eye-brain system ignores most differences of colour temperature in daily life, accepting all but the most extreme examples as white light. In professional cinematography, we choose a white balance either to render colours as our eyes perceive them or for creative effect.

6000K HMI lighting photographed at 3200K to give a moonlight feel to “Heretiks”

Most cameras today have a number of white balance presets, such as tungsten, sunny day and cloudy day, and the options to dial in a numerical colour temperature directly or to tell the camera that what it’s currently looking at (typically a white sheet of paper) is indeed white. These work by applying or reducing gain to the red or blue channels of the electronic image.

Interestingly, this means that all cameras have a “native” white balance, a white balance setting at which the least total gain is applied to the colour channels. Arri quotes 5,600K for the Alexa, and indeed the silicon in all digital sensors is inherently less sensitive to blue light than red, making large amounts of blue gain necessary under tungsten lighting. In an extreme scenario – shooting dark, saturated blues in tungsten mode, for example – this might result in objectionable picture noise, but the vast majority of the time it isn’t an issue.

Left: daylight white balance preset (5,600K). Right: tungsten white balance preset (3,200K)
Left: daylight white balance preset (5,600K). Right: tungsten white balance preset (3,200K)

The difficulty with white balance is mixed lighting. A typical example is a person standing in a room with a window on one side of them and a tungsten lamp on the other. Set your camera’s white balance to daylight (perhaps 5,600K) and the window side of their face looks correct, but the other side looks orange. Change the white balance to tungsten (3,200K) and you will correct that side of the subject’s face, but the daylight side will now look blue.

Throughout much of the history of colour cinematography, this sort of thing was considered to be an error. To correct it, you would add CTB (colour temperature blue) gel to the tungsten lamp or perhaps even place CTO (colour temperature orange) gel over the window. Nowadays, of course, we have bi-colour and RGB LED fixtures whose colour temperature can be instantly changed, but more importantly there has been a shift in taste. We’re no longer tied to making all light look white.

A practical light of the “wrong” colour temperatures in “Finding Hope”

To give just one example, Suzie Lavelle, award-winning DP of Normal People, almost always shoots at 4,300K, halfway between typical tungsten and daylight temperatures. She allows her practical lamps to look warm and cozy, while daylight sources come out as a contrasting blue.

It is important to understand colour temperature as a DP, so that you can plan your lighting set-ups and know what colours will be obtained from different sources. However, the choice of white balance is ultimately a creative one, perhaps made at the monitor, dialling through the kelvins to see what you like, or even changed completely in post-production.

The Art and Science of White Balance

Exposure Part 2: Neutral Density (ND) Filters

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.

IR pollution increases with successively stronger ND filters (left to right) used on a Blackmagic Micro Cinema Camera. The blue dyes in this costume evidently reflect a large amount of IR.

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.

Learn how to use ND filters practically with my Cinematic Lighting online couse. Enter voucher code INSTA90 for an amazing 90% off.

Exposure Part 2: Neutral Density (ND) Filters

Exposure Part 1: Aperture

This is the first in a series of posts where I will look in detail at the four means of controlling the brightness of a digital video image: aperture, neutral density (ND) filters, shutter angle and ISO. It is not uncommon for newer cinematographers to have only a partial understanding of these topics, enough to get by in most situations; that was certainly the case with me for many years. The aim of this series is to give you an understanding of the underlying mechanics which will enable you to make more informed creative decisions.

You can change any one of the four factors, or any combination of them, to reach your desired level of exposure. However, most of them will also affect the image in other ways; for example, aperture affects depth of field. One of the key responsibilities of the director of photography is to use each of the four factors not just to create the ideal exposure, but to make appropriate use of these “side effects” as well.

 

f-stops and t-stops

The most common way of altering exposure is to adjust the aperture, a.k.a. the iris, sometimes described as changing “the stop”. Just like the pupil in our eyes, the aperture of a photographic lens is a (roughly) circular opening which can be expanded or contracted to permit more or less light through to the sensor.

You will have seen a series of numbers like this printed on the sides of lenses:

1      1.4      2      2.8      4      5.6      8      11      16      22     32

These are ratios – ratios of the lens’ focal length to its iris diameter. So a 50mm lens with a 25mm diameter iris is at f/2. Other lengths of lens would have different iris diameters at f/2 (e.g. 10mm diameter for a 20mm lens) but they would all produce an image of the same brightness. That’s why we use f-stops to talk about iris rather than diameters.

But why not label a lens 1, 2, 3, 4…? Why 1, 1.2, 2, 2.8…? These magic numbers are f-stops. A lens set to f/1.4 will let in twice as much light as (or “one stop more than”) a lens set to f/2, which in turn will let in twice as much as one set to f/2.8, and so on. Conversely, a lens set to f/2.8 will let in half as much light as (or “one stop less than”) a lens set to f/2, and so on. (Note that a number between any of these f-stops, e.g. f/1.8, is properly called an f-number, but not an f-stop.) These doublings or halvings – technically known as a base-2 logarithmic scale – are a fundamental concept in exposure, and mimic our eyes’ response to light.

If you think back to high-school maths and the πr² squared formula for calculating the area of a circle from its radius, the reason for the seemingly random series of numbers will start to become clear. Letting in twice as much light requires twice as much area for those light rays to fall on, and remember that the f-number is the ratio of the focal length to the iris diameter, so you can see how square roots are going to get involved and why f-stops aren’t just plain old round numbers.

If you’re shooting with a cine lens, rather than a stills lens, you’ll see the same series of numbers on the barrel, but here they are T-stops rather than f-stops. T-stops are f-stops adjusted to compensate for the light transmission efficiency. Two different lenses set to, say, f/2 will not necessarily produce equally bright images, because some percentage of light travelling through the elements will always be lost, and that percentage will vary depending on the quality of the glass and the number of elements. A lens with 100% light transmission would have the same f-number and T-number, but in practice the T-number will always be a little bigger than the f-number. For example, Cooke’s 15-40mm zoom is rated at a maximum aperture of T2 or f/1.84.

 

Fast and slow lenses

When buying or renting a lens, one of the first things you will want to know is its maximum aperture. Lenses are often described as being fast (larger maximum aperture, denoted by a smaller f- or T-number like T1.4) or slow (smaller maximum aperture, denoted by a bigger f- or T-number like T4). These terms come from the fact that the shutter speed would need to be faster or slower to capture the same amount of light… but more on that later in the series.

Faster lenses are generally more expensive, but that expense may well be outweighed by the savings made on lighting equipment. Let’s take a simple example, and imagine an interview lit by a 4-bank Kino Flo and exposed at T2.8. If our lens can open one stop wider (known as stopping up) to T2 then we double the amount of light reaching the sensor. We can therefore halve the level of light – by turning off two of the Kino Flo’s tubes or by renting a cheaper 2-bank unit in the first place. If we can stop up further, to T1.4, then we only need one Kino tube to achieve the same exposure.

 

Side effects

One of the first things that budding cinematographers learn is that wider apertures make for a smaller depth of field, i.e. the range of distances within which a subject will be in focus is smaller. In simple terms, the background of the image is blurrier when the depth of field is shallower.

It is often tempting to go for the shallowest possible depth of field, because it feels more cinematic and helps conceal shortcomings in the production design, but that is not the right look for every story. A DP will often choose a stop to shoot at based on the depth of field they desire. That choice of stop may affect the entire lighting budget; if you want to shoot at a very slow T14 like Douglas Slocombe did for the Indiana Jones trilogy, you’re going to need several trucks full of lights!

There is another side effect of adjusting the aperture which is less obvious. Lenses are manufactured to perform best in the middle of their iris range. If you open a lens up to its maximum aperture or close it down to its minimum, the image will soften a little. Therefore another advantage of faster lenses is the ability to get further away from their maximum aperture (and poorest image quality) with the same amount of light.

Finally it is worth noting that the appearance of bokeh (out of focus areas) and lens flares also changes with aperture. The Cooke S4 range, for example, renders out-of-focus highlights as circles when wide open, but as octagons when stopped down. With all lenses, the star pattern seen around bright light sources will be stronger when the aperture is smaller. You should shoot tests – like these I conducted in 2017 – if these image artefacts are a critical part of your film’s look.

Next time we’ll look at how we can use ND filters to control exposure without compromising our choice of stop.

Learn how to use exposure practically with my Cinematic Lighting online couse. Enter voucher code INSTA90 for an amazing 90% off.

Exposure Part 1: Aperture

How is Dynamic Range Measured?

The high dynamic range of the ARRI Alexa Mini allowed me to retain all the sky detail in this shot from “Above the Clouds”.

Recently I’ve been pondering which camera to shoot an upcoming project on, so I consulted the ASC’s comparison chart. Amongst the many specs compared is dynamic range, and I noticed that the ARRI Alexa’s was given as 14+ stops, while the Blackmagic URSA’s is 15. Having used both cameras a fair bit, I can tell you that there’s no way in Hell that the Ursa has a higher dynamic range than the Alexa. So what’s going on here?

 

What is dynamic range?

To put it simply, dynamic range is the level of contrast that an imaging system can handle. To quote Alan Roberts, who we’ll come back to later:

This is normally calculated as the ratio of the exposure which just causes white clipping to the exposure level below which no details can be seen.

A photosite on a digital camera’s sensor outputs a voltage proportional to the amount of light hitting it, but at some point the voltage reaches a maximum, and no matter how much more light you add, it won’t change. At the other end of the scale, a photosite may receive so little light that it outputs no voltage, or at least nothing that’s discernible from the inherent electronic noise in the system. These upper and lower limits of brightness may be narrowed by image processing within the camera, with RAW recording usually retaining the full dynamic range, while linear Rec. 709 severely curtails it.

In photography and cinematography, we measure dynamic range in stops – doublings and halvings of light which I explain fully in this article. One stop is a ratio of 2:1, five stops are 32:1, thirteen stops are almost 10,000:1

It’s worth pausing here to point out the difference between dynamic range and latitude, a term which is sometimes regarded as synonymous, but it’s not. The latitude is a measure of how much the camera can be over- or under-exposed without losing any detail, and is dependent on both the dynamic range of the camera and the dynamic range of the scene. (A low-contrast scene will allow more latitude for incorrect exposure than a high-contrast scene.)

 

Problems of Measurement

Before digital cinema cameras were developed, video had a dynamic range of about seven stops. You could measure this relatively easily by shooting a greyscale chart and observing the waveform of the recorded image to see where the highlights levelled off and the shadows disappeared into the noise floor. With today’s dynamic ranges into double digits, simple charts are no longer practical, because you can’t manufacture white enough paper or black enough ink.

For his excellent video on dynamic range, Filmmaker IQ’s John Hess built a device fitted with a row of 1W LEDs, using layers of neutral density gel to make each one a stop darker than its neighbour. For the purposes of his demonstration, this works fine, but as Phil Rhodes points out on RedShark News, you start running into the issue of the dynamic range of the lens.

It may seem strange to think that a lens has dynamic range, and in the past when I’ve heard other DPs talk about certain glass being more or less contrasty, I admit that I haven’t thought much about what that means. What it means is flare, and not the good anamorphic streak kind, but the general veiling whereby a strong light shining into the lens will raise the overall brightness of the image as it bounces around the different elements. This lifts the shadows, producing a certain amount of milkiness. Even with high contrast lenses, ones which are less prone to veiling, the brightest light on your test device will cause some glare over the darkest one, when measuring the kind of dynamic range today’s cameras enjoy.

 

Manufacturer Measurements

Going back to my original query about the Alexa versus the URSA, let’s see exactly what the manufacturers say. ARRI specifically states that its sensor’s dynamic range is over 14 stops “as measured with the ARRI Dynamic Range Test Chart”. So what is this chart and how does it work? The official sales blurb runs thusly:

The ARRI DRTC-1 is a special test chart and analysis software for measurement of dynamic range and sensitivity of digital cameras. Through a unique stray light reduction concept this system is able to accurately measure up to 15.5 stops of dynamic range.

The “stray light reduction” is presumably to reduce the veiling mentioned earlier and provide more accurate results. This could be as simple as covering or turning off the brighter lights when measuring the dimmer ones.

I found a bit more information about the test chart in a 2011 camera shoot-out video, from that momentous time when digital was supplanting film as the cinematic acquisition format of choice. Rather than John Hess’s ND gel technique, the DRTC-1 opts for something else to regulate its light output, as ARRI’s Michael Bravin explains in the video:

There’s a piece of motion picture film behind it that’s checked with a densitometer, and what you do is you set the exposure for your camera, and where you lose detail in the vertical and horizontal lines is your clipping point, and where you lose detail because of noise in the shadow areas is your lowest exposure… and in between you end up finding the number of stops of dynamic range.

Blackmagic Design do not state how they measure the dynamic range of their cameras, but it may be a DSC Labs Xlya. This illuminated chart boasts a shutter system which “allows users to isolate and evaluate individual steps”, plus a “stepped xylophone shape” to minimise flare problems.

Art Adams, a cinema lens specialist at ARRI, and someone who’s frequently quoted in Blain Brown’s Cinematography: Theory & Practice, told Y.M. Cinema Magazine:

I used to do a lot of consulting with DSC Labs, who make camera test charts, so I own a 20-stop dynamic range chart (DSC Labs Xyla). This is what most manufacturers use to test dynamic range (although not ARRI, because our engineers don’t feel it’s precise enough) and I see what companies claim as usable stops. You can see that they are just barely above the noise floor.

 

Conclusions

Obviously these ARRI folks I keep quoting may be biased. I wanted to find an independent test that measures both Blackmagics and Alexas with the same conditions and methodology, but I couldn’t find one. There is plenty of anecdotal evidence that Alexas have a bigger dynamic range, in fact that’s widely accepted as fact, but quantifying the difference is harder. The most solid thing I could find is this, from a 2017 article about the Blackmagic Ursa Mini 4.6K (first generation):

The camera was measured at just over 14 stops of dynamic range in RAW 4:1 [and 13 stops in ProRes]. This is a good result, especially considering the price of the camera. To put this into perspective Alan measured the Canon C300 mkII at 15 stops of dynamic range. Both the URSA Mini 4.6 and C300 mkII are bettered by the ARRI Alexa and Amira, but then that comes as no surprise given their reputation and price.

The Alan mentioned is Alan Roberts, something of a legend when it comes to testing cameras. It is interesting to note that he is one of the key players behind the TLCI (Television Lighting Consistency Index), a mooted replacement for CRI (Colour Rendering Index). It’s interesting because this whole dynamic range business is starting to remind me of my investigation into CRI, and is leading me to a similar conclusion, that the numbers which the manufacturers give you are all but useless in real-world cinematography.

Whereas CRI at least has a standardised test, there’s no such thing for dynamic range. Therefore, until there is more transparency from manufacturers about how they measure it, I’d recommend ignoring their published values. As always when choosing a camera, shoot your own tests if at all possible. Even the most reliable numbers can’t tell you whether you’re going to like a camera’s look or not, or whether it’s right for the story you want to tell.

When tests aren’t possible, and I know that’s often the case in low-budget land, at least try to find an independent comparison. I’ll leave you with this video from the Slanted Lens, which compares the URSA Mini Pro G2 with the ARRI Amira (which uses the same Alev III sensor as the Alexa). They don’t measure the dynamic range, but you can at least see the images side by side, and in the end it’s the images that matter, not the numbers.

How is Dynamic Range Measured?

8 Things to Look For When Buying a Cinema Camera

A couple of weeks ago I shared my thoughts about whether a director of photography should own equipment. My conclusion was that it can be useful early in your career, when you’re shooting corporates or tiny films with no hire budget. So what is the best camera for indie cinematography?

I’m not going to answer that, but I will tell you what to look for when investing in a camera. Hopefully these tips will help you choose the one that’s right for you from the huge and ever-changing array of professional cameras on the market, from the humble DSLR to the ubiquitous Reds and everything in between.

 

1. Image quality

Shooting on a Sony FS7 for “Finding Hope”

The quality of the image is of course the most imporant attribute of any camera. Rather than any technical specifications, I’m talking about the aesthetic quality here: how does it feel? Does it have that elusive “cinematic” quality? Is it “filmic”? Does it remind you of certain kinds of movies?

A good place to start is to look up sample footage on YouTube, or better still Vimeo for less compression muddying the issue. If you can borrow the camera and try it out before you buy, even better. Take away some test footage and try grading it too.

 

2. Resolution

Resolution, the sheer number of pixels a camera can record, is part of image quality, but I include it as a separate point because I see it as more of a technical consideration than an aesthetic one. You should ask yourself what longevity you require from your films – will people still be watching them, say two or three years from now, and if so what sort of resolution might be the norm by then?

Also consider your delivery platform. If everything you shoot is going on YouTube, perhaps you don’t need more than 1080P (standard HD).

 

3. Dynamic Range

Dynamic range is a measure of how much contrast a camera can handle. Too small a dynamic range and you will frequently struggle with bright areas “clipping” – i.e. losing details – or dark areas getting lost in the image noise. Also, the wider the dynamic range, the more flexibility you will have in grading.

For a cinematic image, 12 stops of dynamic range is the absolute minimum, with 14 or more being ideal.

 

4. Maximum ISO

Some ISO tests I conducted on an Arri Alexa Classic in 2017

The ISO (International Standards Organisation) scale rates the light sensitivity of a camera. The most important thing is the native ISO, the one at which the camera is optimised to give the cleanest image with the most detail. On some cameras, setting an ISO other than the native one reduces the image quality considerably.

The higher the ISO, the less light will be required to expose an image correctly. 800 is typical these days, but many cameras go much higher than that. It is worth thinking about spending more money to get a camera with a higher native ISO, because you may save a lot of money on lighting.

 

5. Lens Mount

This is crucial because you may already have a collection of lenses, or you may intend to hire certain lenses, and you need to be sure that they will fit your new camera’s mount.

The Canon EF mount is extremely common and will open up a huge range of options for stills glass as well as some low-end cinema glass. The smaller MFT (micro four-thirds) mount also has a wide range of lenses.

Top-end cameras have PL mounts which take all the beautiful cinema lenses used on big movies, but only choose this route if you are willing to part with a lot of cash!

 

6. Form Factor

A Blackmagic Micro Cinema Camera, not so micro once it’s rigged with rails, matte box, wireless follow focus, battery, monitor and video transmitter!

When I started in the industry, cameras were all ergonomically designed to sit on your shoulder, with a nice handgrip to the right of the lens and an EVF (electronic viewfinder) to provide a third point of stabilising contact. Nowadays cameras tend to be boxy, heavy and uncomfortable to hold without additional accessories (see below).

Again, try to gets your hands on the camera in a shop and see how it feels before you purchase. As well as handheld shooting, consider how easy it will be to rig onto dollies, sliders, gimbals, etc.

 

7. Required Accessories

Buying the camera body itself is unlikely to be the end of your expenditure. You will need lenses, batteries, a battery charger, cards, a card reader and almost certainly some kind of stabilising system, be it a simple shoulder rig or an electronic gimbal.

You may also want an EVF, a tripod, matte box, follow focus – the list can seem endless! Be careful to budget your essential accessories before buying the camera. Some cameras seem like bargains until you add up all the extras. Pay particular attention to the media, and to exactly what speed of media you need in order to shoot at the resolution and frame rate that you require, as this can get very expensive.

 

8. Codec

What file type and codec does the camera shoot? Does your editing system support that format? If not, how time-consuming will it be to convert everything?

What compression ratios does the camera support? How much hard drive space will you need to store an hour of footage at that ratio? What about ten hours, plus back-ups? Often there is a trade-off between a highly compressed format like H.264 which is light on disc space but may need converting before you can edit it, and a lightly compressed format like ProRes which burns through disc space but can be dropped straight into most editing software.

8 Things to Look For When Buying a Cinema Camera

Should DPs Own Equipment?

Recently I discovered Tailslate, a podcast by DPs Ed Moore, BSC and Benedict Spence. The second episode focuses on equipment, and the two men discuss the pros and cons of having your own gear. I have some pretty strong feelings on this myself, so I thought I’d share them here.

I owned equipment for the first 17 years of my career. I was fortunate that at the time I first went freelance (late 1999) I had a small inheritance which I was able to invest in the wonderful new Mini-DV/Firewire technology that had recently emerged. I bought my first semi-professional camera, a Canon XM-1, along with a decent Manfrotto 501/520 tripod, a basic tracking dolly, sound gear, and for editing a PowerMac G4, Mini-DV/VHS deck and a pair of Yamaha MSP5 active nearfield speakers. (The speakers are the only things I still have, and I’m using them as I write, 20 years on. They are the best thing I’ve ever bought. Nothing else has ever served me for so long, so frequently and so reliably.)

Shooting on my Canon XL1-S back in 2003

Apart from the speakers, everything else got replaced every few years as it fell into obsolescence or simply packed up. The XM-1 was replaced with an XL-1S, then I moved onto HDV with a Sony A1, then onto DSLRs with a Canon 600D/T3i, then a Blackmagic Production Camera, which turned out to be my last camera.

Immediately you can see one of the key problems with owning equipment: the fast pace of technological progression and the need to upgrade regularly to keep up. But owning equipment had disadvantages even before the fast-paced digital revolution. In a fascinating Clubhouse Conversation from the American Society of Cinematographers, M. David Mullen, ASC recounts his own experience with gear:

I ended up never owning a camera package. Because of that, I shot mostly 35mm in my early days… People I know who bought a [super]-16 camera, they ended up shooting [super]-16 films for the next ten years or so. So you can get tied to your own equipment.

But there are benefits to owning kit, of course. Corporate clients expect you to provide the gear yourself or to hire it in without any fuss. Clearly the former allows you to make more money from these jobs.

My last camera, the Blackmagic Production Camera 4K

For creative jobs, things aren’t so cut and dried. Owning a camera will certainly get you more work of a certain type. That type is unpaid and low-paid. If you expect to charge a hire fee on your gear, forget it. The type of productions that want you to have your own gear is the type that can’t afford to hire, either from you or from a facilities house. They’ll expect you to come along and bring your gear for free.

We all need to do this type of work at the start of our careers, which is why owning equipment is great at that point. But ultimately I sold my Blackmagic in 2017 and didn’t replace it because I no longer wanted that type of work.

I think things are a little different if you can afford to own a high-end camera. I’m pretty certain that I’ve lost jobs in the past, despite being a better cinematographer than the successful applicant, because they had a Red and I only had a DSLR or a Blackmagic. If you can afford an Alexa then you might well be able to get quality jobs off the back of it, but most of us aren’t in that position!

A camera that I could never afford to buy

The best thing about not owning gear is that you’re free to select the best equipment to tell each particular story (budget and production mandates notwithstanding). Each production is different, and there is no single camera or lens set that is best for all of them. Resolution, high frame rates, colour science, contrast, sharpness, weight, size, cost – all these factors and more influence a DP’s choice, and it’s a critical choice to make. If you’re pushing your own camera or lenses to the production just so you can recoup some of the cash you spent to buy them, you’re doing the story a disservice.

In conclusion, whether or not to invest equipment depends on your budget and the type of work you want to do. But if you’re shooting a drama, even if you own equipment, you should be asking yourself what camera and lenses will best set the tone and tell this story.

Should DPs Own Equipment?

Pinhole Results

In my last couple of posts I described making and shooting with a pinhole attachment for my 35mm Pentax P30t SLR. Well, the scans are now back from the lab and I’m very pleased with them. They were shot on Fujifilm Superia Xtra 400.

As suspected, the 0.7mm pinhole was far too big, and the results are super-blurry:

See how contemptuous Spike is of this image. Or maybe that’s just Resting Cat Face.

The 0.125mm hole produced much better results, as you can see below. My f/stop calculations (f/365) seem to have been pretty close to the mark, although, as is often the case with film, the occasions where I gave it an extra stop of exposure produced even richer images. Exposure times for these varied between 2 and 16 seconds. Click to see them at higher resolution.

I love the ethereal, haunting quality of all these pictures, which recalls the fragility of Victorian photographs. It’s given me several ideas for new photography projects…

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Pinhole Results

Adventures with a Pinhole

Last week I discussed making a pinhole for my Pentax 35mm SLR. Since then I’ve made a second pinhole and shot a roll of Fujifilm Superia X-tra 400 with them. Although I haven’t had the film processed yet, so the quality of the images is still a mystery, I’ve found shooting with a pinhole to be a really useful exercise.

My Pentax P30T fitted with a 0.125mm pinhole attachment

 

A Smaller Pinhole

Soon after my previous post, I went out into the back garden and took ten exposures of the pond and the neighbour’s cat with the 0.7mm pinhole. By that point I had decided that the hole was almost certainly too big. As I noted last week, Mr Pinhole gives an optimal diameter of 0.284mm for my camera. Besides that, the (incredibly dark) images in my viewfinder were very blurry, a sign that the hole needed to be smaller.

Scans of my two pinholes

So I peeled the piece of black wrap with the 0.7mm pinhole off my drilled body cap and replaced it with another hole measuring about 0.125mm. I had actually made this smaller hole first but rejected it because absolutely nothing was visible through the viewfinder, except for a bit of a blur in the centre. But now I came to accept that I would have to shoot blind if I wanted my images to be anything approaching sharp.

The 0.125mm(ish) pinhole magnified in Photoshop

I had made the 0.125mm hole by tapping the black wrap with only the very tip of the needle, rather than pushing it fully through. Prior to taping it into the body cap, I scanned it at high resolution and measured it using Photoshop. This revealed that it’s a very irregular shape, which probably means the images will still be pretty soft. Unfortunately I couldn’t see a way of getting it any more circular; sanding didn’t seem to help.

Again I found the f-stop of the pinhole by dividing the flange focal distance (45.65mm) by the hole diameter, the result being about f/365. My incident-light meter only goes up to f/90, so I needed to figure out how many stops away from f/365 that is. I’m used to working in the f/1.4-f/22 range, so I wasn’t familiar with how the stop series progresses above f/90. Turns out that you can just multiply by 1.4 to roughly find the next stop up, so after f/90 it’s 128, then 180, then 256, then 358, pretty close to my f/365 pinhole. So whatever reading my meter gave me for f/90, I knew that I would need to add 4 stops of exposure, i.e. multiply the shutter interval by 16. (Stops are a base 2 logarithmic scale. See my article on f-stops, T-stops and ND filters for more info.)

 

The Freedom of Pinhole Shooting

I’ve just spent a pleasant hour or so in the garden shooting the remaining 26 exposures on my roll with the new 0.125mm pinhole. Regardless of how the photos come out, I found it a fun and fascinating exercise.

Knowing that the images would be soft made me concentrate on colour and form far more than I normally would. Not being able to frame using the viewfinder forced me to visualise the composition mentally. And as someone who finds traditional SLRs very tricky to focus, it was incredibly freeing not to have to worry about that, not to have to squint through the viewfinder at all, but just plonk the camera down where it looked right and squeeze the shutter.

Of course, before squeezing the shutter I needed to take incident-light readings, because the TTL (through the lens) meter was doing nothing but flash “underexposed” at me. Being able to rely solely on an incident meter to judge exposure is a very useful skill for a DP, so this was great practice. I’ve been reading a lot about Ansel Adams and the Zone System lately, and although this requires a spot reflectance meter to be implemented properly, I tried to follow Adams’ philosophy, visualising how I wanted the subject’s tones to correspond to the eventual print tones. (Expect an article about the Zone System in the not-too-distant future!)

 

D.I.Y. pinhole Camera

On Tuesday night I went along to a meeting of Cambridge Darkroom, the local camera club. By coincidence, this month’s subject was pinhole cameras. Using online plans, Rich Etteridge had made up kits for us to construct our own complete pinhole cameras in groups. I teamed up with a philosophy student called Tim, and we glued a contraption together in the finest Blue Peter style. The actual pinholes were made in metal squares cut from Foster’s cans, which are apparently something Rich has in abundance.

DIY pinhole camera

I have to be honest though: I’m quite scared of trying to use it. Look at those dowels. Can I really see any outcome of attempting to load this camera other than a heap of fogged film on the floor? No. I think I’ll stick with my actual professionally-made camera body for now. If the pinhole photos I took with that come out alright, then maaaaaaybe I’ll consider lowering the tech level further and trying out my Blue Peter camera. Either way, big thanks to Rich for taking all that time to produce the kits and talk us through the construction.

Watch this space to find out how my pinhole images come out.

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Adventures with a Pinhole