No, your film camera doesn’t meter light like you think it does

Your camera’s light meter is dumb, and probably doesn’t work quite how you think it does. But it is accurate — you just have to know how to read it.

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Read about film cameras from the 70s and 80s, and you’ll notice that they all share one kind of light meter. It’s a center-weighted-average meter, and it gets you into the ballpark of workable exposure. Reviews of these cameras mention the accuracy of these meters. Some writers claim that they shoot entire rolls of film on automatic, and the pictures come out great.

And those pictures probably do come out great. But not because of the meter.

Dumb, but reliable

Your iPhone is so smart that it can recognize whether or not people in the photo have their eyes closed, and can delay the shot until they’re open again. But your vintage film camera doesn’t even know whether you’re pointing it at a dark wall in the sun, or a white carpet in a dark bedroom. Today we’ll see what a camera’s light meter actually does, and how to interpret it to get the photo we want, almost every time.

How does a light meter work?

You may have heard that a light meter assumes that whatever you point it at is an average gray. It does. And then, when it measures the light reflected from the scene in front of you, the camera does its best to make the scene into an average gray.

It’s a good strategy, if the photo has a mix of shades. But what does this mean, exactly? How does it try to make things grey? And why?

Imagine a photo, printed on paper. Let’s make it black and white, to keep it simple, although this all applies to color. On the paper, some parts of the photo are white. The paper is blank, in effect. It doesn’t matter whether those white parts represent the sun shining directly at the camera, or a white car on a moonless night: The paper can’t be any brighter. Ditto for the black end of the equation.

This is the dynamic range of the paper. We can break it down like this:

Film covers the middle seven of these 'zones.'
Film covers the middle seven of these ‘zones.’

This image shows a hypothetical full range of tones, broken into 11 steps. Black and white film covers roughly the middle seven tones, and photographic paper has an even smaller dynamic range (around four stops). But let’s say it’s the same, for the sake of this explanation.

The job of camera’s light meter, then, is to fit the huge range of real-world brightness into this narrow range of grays, black, and white. It does this by telling how much light to let into the camera. White sails in bright sun? Reduce the light so that white fits. Apples in a dark orchard at sunset? Grab as much light as possible to get them into the gray part of the film’s range.

The camera’s meter manages this by assuming that everything is the same gray as the square in the middle of that chart above1. If you take your meter reading off something that is middle gray, then bingo. It will be rendered perfectly on film. But if you point the meter at something white, or something black, then this happens:

On the left, an indigo denim jacket. On the right, a white wall.
On the left, an indigo denim jacket. On the right, a white wall.

That’s a dark blue denim jacket in the shade, and a white wall in the sun. Both are recorded as middle gray (both photos were taken with a digital SLR set to center-weighted dumbo mode) if you follow the light meter’s instructions.

What about auto exposure?

When you use auto exposure on an old film camera, all it does is transfer the meter reading to the camera’s aperture and shutter speed settings. It’s the same as manual, only it twists the knobs for you. If the overall scene is darker than average, it will be rendered too light. And vice versa. And that’s with simple lighting situations.

If the scene is tricky, or its dynamic range far exceeds that of the film, then your camera will be as confused as you are. The classic example is a backlit portrait. You want to see the subject’s face, but the camera’s meter is overwhelmed by the bright background. What you end up with is a silhouette. Some cameras have a backlight button that you can press. This just adds two stops to the exposure, getting enough light to show the subject’s face.

So how come all these film photos come out so good?

There are three reasons that your film photos almost always come out well, despite all this. One is that, often, the mix of tones in scene in front of you does average out to a middle gray, or close enough. In these cases, the meter’s design matches up to the real world, and everyone’s happy.

Another reason is that negative film has a large tolerance to overexposure. Even if you open up an extra three stops, it will still render details in the whites. B&W film can be even more tolerant. This is called exposure latitude, and it in one reason that it’s almost impossible to “blow” highlights on film. If you’re using slide film, then you should never overexpose it. It’ll blow just like digital.

The final thing that saves your shots is that the photo lab that develops and prints your photos makes the best prints it can from your badly-exposed negatives. The only thing that really ruins a photo shot on negative film is underexposure. Take a look at an underexposed negative and it looks “thin.” There’s little to no detail in the shadows, and there’s no bringing that back. A print made from one of these exposures is gray, lacks contrast, and has a lot of noise (grain). So, our first tip is, if in doubt, overexpose negatives a little, and underexpose slides and digital.

How are you supposed to use a film camera then?

The only way to get consistently good exposures on an old film camera is to take charge. You can’t just put it in auto, then point and shoot. Even if you’re snapping the most common shot, a portrait with the subject’s face taking up most of the frame, the exposure will be off. A typical caucasian face is one stop above middle gray, so your camera will make it gray, which is one stop too dark. Light-toned black skin is about middle gray.

Taking charge can mean always shooting in manual. You could meter off the face of your white friend, and open up one stop to compensate. I like this method because the camera settings are then fixed. Even if you move away so your subject is smaller in the frame, the exposure of their face is still good. Only if they move into different light do you need to re-meter. It’s fast, and easy.

You can also use the auto mode, and then use the camera’s exposure-compensation dial to tweak the result. This method suffers from unpredictability. If the framing changes, the meter reading will, too, and maybe the compensation you chose is no longer what you want.

Another trick is to buy a film camera with fancy metering, either a Nikon with Matrix metering, or a Canon with Evaluative metering, or something similar. Something ugly from the 1990s is a good idea. These will meter as well as an early digital camera, and you really can just let the camera take care of it all. The Nikon still gets fooled by backlighting and high-contrast scenes though, and is useless in nighttime streets. The Canon is probably as bad, but I haven’t used one for years.

I prefer to use manual. It seems less convenient, but instead of having to constantly second-guess the camera’s reading, you can just take charge and do it yourself. Once you get used to it, it’s pretty easy. Go and read a few guides, and use the tips for metering off blue sky, green grass, or your own hand. They work really well, and are totally predictable.

Just don’t let the camera decide for you.

  1. Almost. The middle gray in this kind of chart is 18% gray, whereas most light meters assume 12.5% gray.
    That’s a half stop difference, so if you use a gray card to help you with your readings, you should open up a half a stop to compensate.

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