Metering Light 101 – The Dynamic Range

So, you want to be a cinematographer? Look cool with a big camera like this guy on the right? (This guy is Roger Deakins. If you know his body of work, he needs no introduction. If you don’t, check it out.) Perhaps you’re playing it modest and would like to just shoot better videos on whatever camera you have, be it a smartphone, a DSLR or and old Super 8 camera?

Whatever is your goal, you need to understand what Roger is doing on the second picture. What is that strange little box in his hand? And what is he looking at?

It is a light meter. And he is taking a reading to see how much light there is so that he could either decide on the aperture he’ll be using or the amount of light that he still needs to add (or take away) from his scene.

Metering light. This is what cinematographers do. Or at least used to do.

WHY DO I NEED TO METER LIGHT? CAN’T I BE A DOP WITHOUT UNDERSTANDING IT?

No, you can’t.

Light is what you’re working with. You need to understand not only its creative aspects (which takes a lifetime) but also its technical side (which definitely doesn’t take a lifetime).

But so that you’d understand the ‘why’, let me give you a less authoritative and more logical answer.

DYNAMIC RANGE

Dynamic range is the reason why we need to meter light. It is a simple concept: for any device (including our brains) dynamic range is the difference between the darkest blacks and the brightest whites that the device is capable of capturing or reproducing.

(I have written a very simple article to explain the basics of dynamic range on ExposureWorks, you can read it here. There is also a bit more advanced post illustrating the concept of latitude, read it here.)

Dynamic range is often also called latitude. Don’t be confused, these terms refer to exactly the same thing.

Imagine a bright, sunny day. A garden bathing in sunshine, water glimmering in a small pool, a blue sky with beautiful white clouds. This is your weekend cottage house and you’re sitting inside your living room, looking at it all from your armchair, shielded from the heat and the light by Venetian blinds. Enveloped in pleasant dimness, in spite of the amazing light outside, you’re reading your favourite book by the light of a small reading lamp.

No, I’m not making it all up! You’ve seen similar scenes in films. And you have definitely seen this one!

Imagine what would happen if Don Corleone threw the windows open at the end of the scene and gazed at the garden party. If you were physically there, you would first squint a bit (while your pupils, i.e. the biological aperture of your eyes adjust) but you wouldn’t have a problem perceiving both the garden party and Don Corleone’s face in the window at one and the same time!

It is because the dynamic range of the human visual system is amazing. It is so amazing, that we don’t even notice it’s there, not until we run into extreme situations like not being able to see the details of the face of someone standing right in front of the sun. If the dynamic range of a natural scene can easily exceed the limits of human vision, just imagine how much more it will exceed the capabilities of a £400 DSLR!

As a cinematographer, you also need to think about film, even if it’s already history to most of us. Or if you’d prefer, ponder about the horrors of early digital filmmaking dominated by formats like VHS, Betamax, hi8, miniDV or HDV – formats with incredibly limited dynamic ranges.

CHALLENGE

Could you shoot in a single take Don Corleone standing inside, in front of the window and then throwing the blinds open, leaning outside the window, taking in the sight of the merry crowd enjoying the sunlit garden birthday party?

Yes, you could. But even with the highest-end digital cameras, you would need to adjust your aperture during the shot. Many filmmakers do it and many DOPs are extremely skilled at ‘camouflaging’ the adjustment with camera movement or how they block the scene.

YOU NEED TO METER LIGHT AND GET YOUR EXPOSURE RIGHT SIMPLY BECAUSE THE DYNAMIC RANGE OF YOUR CAMERA IS LIMITED. IF IT WEREN’T LIMITED, YOU COULD JUST PUSH THE RED BUTTON AND ‘DO IT IN POST’.

NEXT

Now that we understand why we need to meter light, let’s see how it’s done.

Continue to Part 2: The Medium Grey