Exposure - Taking Better Pictures Tutorial 1

by travis_cooper Mon Feb 25, 2008 3:46 pm

This is the first installment of my tutorials on taking better pictures with your camera. This is directed mostly to beginners, but all are welcome to read them and ask questions. You never know when hearing something a different way may get things clicking in your brain.

The first thing to learn about photography is exposure. Exposure is really critical in photography, because if you don't have the correct exposure your picture won't look like you want it. The other thing that will come from learning exposure is to get you to stop using your auto settings in your camera. While these settings can be good, they are also limiting, because they allow the camera to make important decisions rather than you making them.

There are 3 things that control the exposure your film, or in digital your sensor, receives from light. These three things all work together in achieving what your camera wants to see. Your camera wants 18% of the light and considers that proper exposure. So using the 3 elements we try to get to this point. The three things that make up your exposure are aperture value, the size of the opening of the lens, shutter speed, how long the film, or sensor, is receiving light, and ISO, the sensitivity your film has to light.

These three elements work together and in the next tutorials I will cover each individually, when I do so I will talk in full stop values. Although your camera may use half, or even third, stop values I will only talk about full stop values, but you will be able to follow the logic through with your camera even though you may have numbers in between. Since all 3 elements use full stops we can change one and then change one of the other two in the opposite direction and we will receive the exact same exposure. Click on the tutorials below to learn about each of the individual settings then the next part will make more sense.

Now that we have a basic understanding of the three values here is how they can work together. If your camera says it wants f/11 @ 1/4 ISO 100 in order to get proper exposure we can now make a decision. If we have a tripod, since this is kind of a slow shutter speed, we could probably use this for our picture if we want a relatively large dof. Taking a picture of a mountain, or a building might be a good choice for this setting. Lets so that you actually want to have a small dof though, rather than a large one, so you decide to set your f-stop to f/2.8, the lowest stop your lens will let you go. This will give you a pretty small dof, but you are now getting 4 full stops more light hitting your sensor since your aperture is now open wider. So we need to get less light from one, or both, of the other elements. Since we are at ISO 100 we can't go any lower, at least on our camera we can't, so our only option to reduce the light is to speed up our shutter. So we make our shutter 4 stops faster which takes us to 1/60. We now have our camera set at f/2.8 @ 1/60 ISO 100. We take our picture and realize, hey, this is too blurry, I just can't hold my camera still enough at a 1/60 shutter speed. I don't have a tripod and I really need to freeze this motion a little better. So you realize that by raising your ISO you can get more sensitivity to light, meaning you can use a faster shutter speed, but you also know this is going to get you some digital noise. You decide that ISO 400 doesn't introduce too much noise, and that it is probably an acceptable number. So you set your ISO to 400, now you have just added 2 full stops of light. We now need to reduce the light somewhere else by 2 stops. We already know we don't want to close down our aperture because we want to keep it at 2.8, plus we wanted a faster shutter speed anyway, thats why we changed the ISO. So we now set our shutter speed 2 stops faster which takes us to 1/250. Our reading is now at f/2.8 @ 1/250 ISO 400 and we take the picture. This is now looking a lot better, we stopped the motion with the fast shutter speed, we got a nice blurry background with our low f-stop giving us that nice small dof, and our ISO isn't too high to produce too much noise. This is just an example of how we can use these 3 elements to work together and how we can make the decisions rather than letting our camera make the decisions.

Go to the next tutorial - Mode Settings
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