Stop letting your camera guess exposure: trust me, manual mode is simpler than you think

Why would you even need to think about exposure? Can’t the camera do that for you? It’s certainly a lot easier to let the camera work out the exposure settings so that you don’t have to, and there are probably countless photographers who’ve never done anything else and still come away with great photos. But not always.

Sometimes the camera captures a shot that’s too dark or too light, or you take a series of shots in the same surroundings, and each one has a slightly different exposure. This happens because the camera doesn’t really understand what it’s looking at, it doesn’t really know what you want, and every time you take another shot, it’s taking another guess at the exposure, even if it’s just your framing or where you’re pointing the camera that’s changed, not the lighting.

Cameras are incredibly good at analyzing light patterns and brightness levels, but do not have a brain to work out what they mean. Fortunately, you, the human behind the camera, do. This is why taking control of exposure is important, even in an age of multi-pattern metering and multi-mode auto-exposure options.

Reciprocity rules

Let’s start with the basic concept of ‘reciprocity’ in exposure. To keep the same exposure but with a faster shutter speed, you have to let more light through with a wider lens aperture. To use a small lens aperture for more depth of field, you need a slower shutter speed (a longer exposure time) to compensate for the lens passing less light through.

So in auto-everything ‘P’ or ‘Program’ mode, the camera works out a combination of lens aperture and shutter speed that’s an all-round compromise between shutter speed (stopping subject movement and camera shake) and lens aperture (a small enough aperture to achieve decent near-to-far sharpness).

If you want to control shutter speed or aperture directly because they are important creative tools for the kind of photographs you’re taking, you can switch to ’S’ (shutter priority) or ‘A’ (aperture priority) mode. You choose the shutter speed or aperture, and the camera adjusts the other one to compensate and still get the correct exposure.

These days, there’s a third exposure control – ISO. Back in the days of film, the sensitivity was fixed by the film you loaded into the camera. Now, with ISO controls, you can change the sensitivity from one shot to the next. ISO, like shutter speed and lens aperture, works on a system of doubling and halving. You can use a shutter speed twice as fast by doubling the ISO, for example. This is why higher ISO settings are so useful in low light – they let you shoot with faster shutter speeds to avoid subject movement or camera shake.

This is the so-called exposure triangle, and you can set your camera up to adjust all three exposure settings automatically or just one or two. That fixes the problem, then, right? Not really, because there’s another problem...

What camera meters don’t know

Cameras can measure the light in a scene in all sorts of clever ways, but still have to guess at what it means. To be fair, modern evaluative/multi-pattern metering modes are now so good that most of the time they are close enough to a decent exposure that you don’t need to worry about it.

But there are lots of things that even the most sophisticated metering system won’t know. It won’t know that wedding dresses are supposed to be white and need more exposure, and it won’t know that black cats are indeed black and need less exposure so that they actually look black.

Indeed, this is why the best light meters can still pull off a trick that in-camera light meters can't – with incident light readings, they can measure the light falling on your subject, not just the light bouncing back. White dresses and black cats? No problem!

Now, as a photographer (and being gifted with actual intelligence, not just the artificial sort), you know this. You don’t need a $500bn AI data center in Nevada to work this out. You can use the camera’s EV compensation control to adjust its automatic exposure setting to make the picture come out lighter or darker. But now you’re having to do more work to override an automatic system, which is surely halfway towards setting the exposure manually yourself.

Another problem is that the camera won’t know what you want the photo to look like. If you shoot a backlit portrait, it won’t know if you want your subject’s face exposed properly or if you want a dramatic silhouette. It’ll have to guess, probably choosing an exposure somewhere in the middle, which doesn’t really do either properly. It’s another situation where you will have to interpret and override the camera’s response to such a degree that you might just as well have done it yourself in the first place.

Enough problems yet? Here’s a final one. The camera will adjust the exposure every time you take a shot, even if nothing has changed in the lighting or the subject, except maybe you’ve moved slightly or adjusted the zoom setting. It has no memory of what it did for the shot before, and no idea that nothing actually needs to change.

This is the fundamental flaw behind all exposure metering systems. They are measuring devices that need interpretation. Sometimes you don’t need to interfere with the settings, but often you do. You can do this with the EV compensation dial or with the AE-L button, but either way, you’re having to step in and override what the camera was going to do.

There comes a point when surely it’s simpler to work out for yourself what the exposure needs to be, set the exposure manually, and leave the camera’s auto-exposure system out of the equation entirely. You can do this with the camera’s in-built meter by measuring and interpreting and applying the exposure yourself, or with a handheld meter, or by using experience or easy guides like the ‘sunny 16’ exposure rule for outdoor photography.

What manual mode does is hand back exposure control to you. Otherwise, you’re just riding shotgun with an automated exposure system and trying to make sure it doesn’t mess up.

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