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.

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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 highlighs 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

The Normal Lens

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.

Asahi Pentax-M 50mm/f1.4 – a normal lens for 35mm stills

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.

Deleted scene from “Ren: The Girl with the Mark” shot on a vintage 28mm Pentax-M

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.

A scene from “The Little Mermaid” which I shot on a 32mm Cooke S4

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.

The Normal Lens

“The Knowledge”: Shooting a Multi-camera Game Show

Robert Jezek as gameshow host Robert O’Reilly. Photo: Laura Radford

Last week saw the UK premier of The Knowledge, an art installation film, at the FLUX Exhibition hosted by Chelsea College of Arts. Conceived by award-winning, multi-disciplinary artist Ian Wolter, The Knowledge comments on the topical issue of artificial intelligence threatening jobs. It takes the form of a fake game show, pitting a team of traditional London cabbies (schooled in the titular Knowledge) against a team of smart-phoning minicab drivers. Although shot entirely on stage, the film’s central conceit is that the teams are each guiding a driver across London, to see whether technology or human experience will bring its car to the finish line first.

You can see a couple of brief promos on Vimeo here. It’s a unique project, and one that I knew would be an interesting challenge as soon as I heard of it from my friend Amanda Stekly, producer and production designer. This week and next I’ll describe the creative and technical decisions that went into photographing the piece, beginning this week with the camera side of things.

Photo: Laura Radford

I had never shot a multi-camera studio production like this before, so my first move was to sit down with my regular 1st AC and steadicam operator Rupert Peddle, and his friend Jack D’Souza-Toulson. Jack has extensive experience operating as part of a multi-camera team for live TV and events. This conversation answered such basic questions as, could the operators each pull their own focus? (yes) and allowed me to form the beginnings of a plan for crew and kit.

At the monitors with Jonnie. Photo: Laura Howard

Ian and Amanda wanted the film to have a dated look, and referenced such eighties quiz shows as 3-2-1 and Blankety Blank. Director Jonnie Howard and I knew that we had to supply the finished film in HD, which ruled out shooting on vintage analogue video cameras. Interlaced recording was rejected for similar reasons, though if memory serves, I did end up shooting at a shutter angle of 360 degrees to produce a more fluid motion suggestive of interlaced material.

I was very keen that the images should NOT look cinematic. Jonnie was able to supply two Canon C100s – which I’ve always thought have a sharp, “video-ish” look – and L-series glass. I set these to 1600 ISO to give us the biggest possible depth of field. For the remaining two cameras, I chose ENG models, a Canon XF-300 (owned by Rupert) and XF-305. In an ideal world, all four cameras would have been ENG models, to ensure huge depth of field and an overall TV look, but some compromise was necessary for budget reasons, and at least they all used Canon sensors. We hired a rack of four matching 9″ monitors so we could ensure a consistent look on set.

Photo: Laura Radford

One Canon C100, with an L-series zoom, was mounted on a pedestal and outfitted with Rupert’s follow focus system, allowing Jack to pull focus from the panning handle. The other C100 would shoot a locked-off wide, and was the first camera to be set up. A 14mm Samyang lens made the set look huge, and I placed it low down to emphasise the map in the foreground, and to make it easy for the other cameras to shoot over it. Once that frame was set, we taped a large V shape on the floor to indicate the edges of the wide shot. As long as the lights and other cameras stayed out of that area, they would be safe.

Jack operates the pedestal-mounted C100. Photo: Laura Radford

Generally Jack’s pedestal-mounted C100 followed the host, Robert Jezek, or captured the interesting moving shots, while Rupert and the third operator, Jimmy Buchanan, cross-shot the two teams on the XF-100 and XF-105. No filtration was used, except for a four-point star filter on one camera when glitter canons are fired at the end of the game. This cheesiness was inspired by the 3-2-1 clips I watched for research, in which star filters were used for the tacky sequences showing the prizes on offer.

Next week I’ll discuss lighting the show. Meanwhile, find out more about Ian’s work at ianwolter.com.

Photo: Laura Radford

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“The Knowledge”: Shooting a Multi-camera Game Show

If Camera was Sound and Sound was Camera

“Sound has the set,” calls the 1st AD, fishing a roll-up from her pocket and heading for the fire exit.

The production sound mixer strides into the middle of the set and strokes his Hipster beard thoughtfully.

“What are you thinking, boss?” asks the gaffer, scratching at the beer belly under his Yamaha t-shirt.

The mixer points to the skylight. “Let’s have some early morning ambience coming through here – the one with the distant traffic.” With a sweeping gesture he encompasses one side of the kitchen set. “I want it to explode off the floor and reverberate throughout this whole area.”

“Hundred watt woofer?” the gaffer suggests. The mixer nods, and a spark scuttles off to the truck for the required speaker.

“Is that practical?” the mixer wonders aloud. The gaffer follows his gaze to the kettle, nods, and flicks the switch. The mixer pulls a sound meter from the pocket of his leather jacket and holds it up to the boiling appliance. “6dB under.”

“We could hide a little tweeter behind it, bring the level up a bit,” the gaffer suggests. “I’ve got half a dozen different kettle effects on the truck.”

The mixer agrees, and proceeds to point out several other positions around the set, which is soon full of busy sparks running XLR cables, rigging speakers and shaping them with sound blankets. A cacophony grows as each one is fired up.

“Does this look about right?” asks the 1st AS, steadying the Sennheiser as the grips wheel its massive Technoboom to the previously agreed spot. She holds a pair of headphones out to the mixer.

He puts them on, and a reverent hush descends upon the set. He pans the mic left, then right, then up, then down, then left and right again. Finally he takes off the cans, clutching at his SQN baseball cap to stop it coming off too. “We need to go tighter,” he pronounces. He holds up his two hands, forming a circular aperture with his fingers, and cups them around his ear. His face a picture of concentration, he squats down and listens intently through the hole in his hands. He shuffles a little to the left. “This is it. We need to be right here on the 67.”

“Copy that,” the 1st AS replies. Her 2nd drags over a massive flight case and she begins unscrewing the ME66 from the power module.

 

“OK everyone, standby for a mic rehearsal.”

At last the camera operator – who had been somehow hiding in plain sight – puts down his coffee and heaves an Alexa onto his shoulder, checking the image as the cast go through the motions.

The director presses her headphones against her ears, frowning. She turns to the mixer. “I’m not getting enough sense of where they are,” she says. “Can we go wider?”

A few moments later the 1st AS is sighing as she unscrews the ME67 and remounts the ME66.

“It’s really quiet,” a producer complains, from his canvas chair in front of the amp at sound city. “Can we turn it up a bit?”

“We’ve got to have the mood,” the mixer insists. “What you can’t hear is more exciting than what you can.”

“I’m paying to hear it!” snaps the producer. “And why is there so much hiss? I can barely hear the dialogue over it.”

“It’s atmosphere!” the mixer protests, but he can see he’s not going to win this one. Reluctantly he signals a spark to turn down the white noise generator.

 

“Cut!” calls the director, smiling in satisfaction at the cast. She turns to the mixer. “How was that for you?”

“That sounded beautiful,” he replies ecstatically.

“OK, moving on,” says the AD, reaching for the clip-list.

“Hang on a minute.”

All eyes turn to the camera op.

“The caterer walked through the back of shot.”

“Did he?” asks the AD, looking around the crew for confirmation.

“I didn’t pick him up,” says the mixer.

The camera op stares at them in disbelief. “He sauntered right across the back of the set. He was there the whole take. It’s completely unusable.”

The AD sighs. “I guess we’d better go again.”

“Can we ask people not to walk through the frame? This lens will pick up literally anyone that walks in front of it.”

The director thinks about this. “Have you got a different lens you can use?”

“Can’t you put Go Pros on them?” asks the AD, gesturing to the cast.

“I’d rather not use Go Pros,” a new voice chimes in. Everyone turns with surprise to see the director of photography blinking in the light. She almost never moves from the shadowy corner where she sits with LiveGrade and a monitor which is rumoured to display mostly rugby matches.

“We can’t afford to lose any more takes because of camera,” says the AD. “What’s wrong with Go Pros anyway?”

“The image just isn’t as good. The dynamic range…”

But the AD cuts her short. “Well, it’s either that or AVR.”

“I just think if we took thirty seconds to find a new position for the Alexa…”

As the producer strides over to stick his oar in, the sound assistants exchange knowing looks: this could go on for a while. The pair lean on the Magliner and check their phones.

“Have you ever worked with a Nagra?” the 2nd AS asks, conversationally. “I still think they sound better than digital.”

If Camera was Sound and Sound was Camera