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Do I Need to Learn Exposure?

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You already know I’m going to say “yes”; but I think there is a little more to it than you might expect.

I approach questions like this with a degree of caution. The reason is that I’ve seen answers from experts in other contexts go horribly wrong.

For example, I’ve always been interested in sailing. I don’t actually do much sailing (and when I do it is often disastrous) but I read a lot about it. Ten or fifteen years ago, people used to send questions to magazines or post questions online asking whether, with the advent of GPS and electronic charts, you really needed to learn how to use a sextant. Old sailors were beside themselves at this preposterous question. Of course you did! What kind of fool would go out to sea relying on some electronic gizmo? It could be wrong. It could get wet or struck by lighting and go out on you. The power could fail. There are all sorts of things that could happen. Sailors had been using sextants and paper charts for hundreds of years and that wasn’t about to change.

Now, of course, just a few years later, everybody just uses electronic charts and GPS.  I’m not sure if even the old salts carry sextants with them anymore.

The same dynamic was present in photography during the change over from film to digital. Film cameras were the best, and these newfangled digital cameras were scoffed at. Even when it became clear that digital was here to stay, old school photographers were insistent that new photographers learn the old ways of film as the “basics” of photography. Except they weren’t really the basics anymore. “Pushing” film, the zone system, and darkroom techniques don’t have a lot of application to digital. With digital photography, it is all about the histogram.

When I hear people ask “with all the advances in cameras, do I really need to learn about exposure?” at first I want to jump up and scream “YES, OF COURSE YOU DO!” But then I realize I might just be acting like those old school sailors or photographers. I mean, lots of cameras actually show you how the picture will be exposed before you take the picture. So, in answering this question, I need to take a step back here.

First, let me say that there are actually a few different levels to this question. We’ll talk about them separately here.

Exposure for the Beginner

The first level is the total newby just getting started with photography. Does this person need to understand the basics of exposure? Yes. I’m pretty clear on this one.

Why? Because while it is true that the camera will take a correct exposure on auto mode almost all the time, that doesn’t mean it will take a proper exposure. What I mean by that is that the camera will get the brightness value right, but there is a lot more to exposure than that. The same three controls on your camera that control the exposure level (i.e. brightness) of the picture also impact a lot of other aspects of your picture. The exposure controls also control things like the depth of field of the picture, the sharpness, whether there will be motion blur, and the amount of digital noise present. These same exposure controls can also be used to create effects like the “starburst” effect on lights and “streaking lights” in traffic.

So these controls do a lot more than just determine the brightness of the picture. If you don’t know what the different shutter speeds, aperture sizes, and ISO values are doing, your picture may have a proper exposure level, but it won’t be any good.

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Consider a simple example. Let’s say you want to take a picture of your spouse. It is basically a head-shot, and you are not interested in the background. You have the camera in automatic mode and take the picture. It will meter the scene and set the shutter speed, aperture size, and ISO. It might set the shutter speed at 1/15th of a second, the aperture at f/11, and the ISO at 400. If the picture is of the brightness value you want, then is it a correct exposure.

But is it a proper exposure? Probably not. The shutter speed is too slow and might introduce some camera shake or motion blur. The aperture is needlessly small. And the ISO should be lowered if possible. I would say something like the following values would be a proper exposure for what you are trying to achieve: shutter speed 1/60, aperture f/4, ISO 200. You could quibble with that, but we’d be close. The point is that you would open up the aperture to reduce depth of field, which would give you more light to work with. Since you have that extra light, you can shorten the shutter speed to eliminate any shake and reduce the ISO a bit to make sure there is no digital noise in your picture.

Both the original settings and the changed settings let in the exact same amount of light and will result in the same brightness value of the picture. So both ways are technically correct. Only the second one is really a proper exposure though. It is the only one that is going to achieve the effect you desire. If you don’t understand exposure, you’ll never get to the proper one.

Advanced Exposure

But now let’s take this a level deeper. Let’s say you already know how shutter speed, aperture, and ISO work in a general sense. You know enough to shoot in Aperture Priority mode and you control your aperture to get the depth of field you want. You know enough to keep your ISO low to avoid digital noise, but at the same time you know not to use too slow of a shutter speed or you will introduce blur (unless you have a tripod). Given that, do you really need to take it any further? Do you need to be able to count stops?

Here my answer changes to “maybe.” You could probably get away with just a basic level of knowledge. That is, you might not need to get into the different measurements, stops, and all that. You can just use a small aperture when you want a deep depth of field and a large aperture when you want a shallow depth of field. Then if your shutter speed is within an acceptable range, you are all set. If not, you just adjust the ISO until you can get the shutter speed where you want it. End of story.

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There are, however, situations where detailed knowledge would be helpful. A pretty clear example is if you use neutral density filters (which I use all the time). If you use a strong neutral density filter, the camera actually cannot see through it, so you are on your own. You’ll have to increase the exposure by the number of stops you took away by adding the filter. This will require you to do some calculations on the fly. For example, if your exposure is set at a shutter speed of 1/120, your aperture at f/8, and ISO at 200, but then you add a 10 stop neutral density filter you will have to increase the exposure by 10 stops. Increasing the length of the shutter speed by 10 stops will take you to 8 seconds. That’s not too hard. But if you want to make changes to your aperture and ISO then things will get trickier.

Another time I end up counting stops a lot is in night photography. Very often I take test shots, but I don’t want to use a really long shutter speed because I don’t want to have to wait for 20 or 30 seconds (or longer). Therefore, I set the ISO at obscenely high levels (think 12,800 and higher) and dial in the exposure level. Then when I am ready to take a real picture, I reduce the ISO to an appropriate level, but make an offsetting move to the shutter speed or aperture. I get the same exposure level but now my picture won’t have all the noise that was in the test shot.

My goal here isn’t to get into the specifics of those moves here, I just want to show you how it might be useful. I get into specifics in other articles like this one. (Of course, if you want to start at the beginning, check out my Exposure Page, which will walk you through all aspects of the process).

A detailed knowledge of exposure will also help you understand the specific effects of the different exposure controls. A great example is when you have moving water in your photo. Do you know how the water will look in a photo taken at 1/20 versus 1/2 versus 5 seconds? (If you don’t I actually wrote an article for DPS some time ago showing some of the differences, which you can find here). I find it enormously helpful to know this. Could you just engage in a little trial and error and keep trying different settings until you got the one you wanted? Sure. But that is hardly optimal.

So, as you can see, there are a few times and places when having a complete grasp of exposure helps. In any event, I personally enjoy having the ability to flick around in Manual mode trying different exposure settings while being confident in what the effect will be. I think it makes me a better photographer. I also think it will make you a slightly better photographer (if you aren’t confident in this already).

But is that really necessary? Probably not. That’s particularly true with the newest cameras that show the exposure level in your LCD before you even take the picture. There, knowing enough to control depth of field, noise, and shake/blur is probably enough.

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