The Trinity of Photography – Aperture, ISO and Shutter Speed


Light is essential to photography, so much so that the word “photography” means “light writing”. For film photography, light waves create a chemical reaction directly on the film making a picture (of sorts). Now light rays hit a little sensor that transmits data to the little computer in the camera. But either way, photography needs light to take pictures.

Let’s liken the photographic process to filling a bucket with a garden hose. The water is light, the bucket is the sensor, the size of the hose is the aperture and the amount of time. We come onto a scene and  we know that we brought a 5 gallon bucket, a hose large enough to transmit 1 gallon of water per minute. We can say that we need to have the hose ON for five minutes to fill the bucket. Lets say we want to fill a 10 gallon bucket. Our options are either to get a bigger diameter hose or keep the hose the same size and simply leave it on for twice as long.

Based on what you are trying to do there is an optimal setting for each aspect of this camera trinity. While there is no line delineating the boundries of right and wrong, there definitely is a transition from good to bad.

Generally speaking you want your ISO as low as possible. The higher the number the more digital noise in introduced. The better cameras are better able to shoot at higher ISOs without being affected by noise. If you don’t know what I mean by noise look at some snapshot you took indoors at night. If you magnify the picture the squiggles of ugly colors shows up.

Shutter speeds are a matter of taste. It requires higher shutter speeds to stop motion. The faster the subject the faster the shutter speed needs to be but also the less light goes to the sensor. This is not a problem UNLESS you needing REALLY fast shutter speeds OR there isn’t much available light.

Aperture is also a matter of taste. The more open the aperture is, the shallower the depth of field (the amount of distance that is in focus). If one is shooting an event, generally a good aperture to shoot at is f8 because this often provides a decent depth of field for allowing a majority of the scene to be in focus. Portrait photographers often open the aperture up to something like 1.8 (or bigger) to provide a very soft blurred background. The smaller the number, the bigger the opening and the more light it lets in. The depth of field issue is different for point and shoots than it is with DSLRs. It is very difficult to get a shallow depth of field (unless using the macro mode) with a compact camera no matter how hard you try. This is both good and bad.

Often we find ourselves in situtation that are not perfect and decisions must be made. Most people let the camera decide without understanding its decision making process. If you use the automatic settings, it may actually work against you. If you use these automatic settings, you need to understand how the prioritize otherwise you could end up with some bad pictures.

Some examples:

  • Suppose you are at a volleyball event. The light is terrible but you want the shutter speed high to freeze movement then you open the aperture as far as possible and then move the ISO up until you get the proper exposure. This will mean noise but that is the sacrifice needed.
  • Suppose you are taking a picture of a landscape but it is early morning. You know that the final output will be a print. Keep the ISO as low as possible, put the aperture to the depth of field you want and slow your shutter speed down to get the correct exposure. This will like result in placing your camera on something solid (like a tripod, monopod or a chair) in order to make the shot.

For the DSLR there are some great choices – Speed Priority, Aperature Priority and Manual.

Speed priority means that the photographer chooses the shutter speed, and in response to the lighting conditions the aperture changes. This seems like a good deal, but I stay away from it because the changing depth of field, for the type of shooting I do, is not a good thing.

Aperture Priority – Choose your aperture size and the shutter speed varies. IF you are doing portraits this is the way to go but you will need to keep an eye on the shutter speed. If it drops too low, then it is necessary to bump up the ISO to get the minimum required speed.

Manual – It is, well, manual. Great for having total control over your camera. It is great if conditions don’t change, as in a studio enviroment but I almost never shoot in the type of conditions that make this handy. There are times I do find myself in a tricky situation an need to resort to manual but not too often.

There are many more examples that I could give but I think you see how this works. Before shooting a scene, the photographer needs to determine what type of shooting she will do, what the final output is (an 11×14 print or simply a small picture for Facebook). This will inform her as to what can be compromised and what can’t.

This is a somewhat simplified look at this issue. It takes awhile to become comfortable and adept at handling light. Hopefully this article clears some things up and encourages you to try some things with your camera.

The camera as three ways to regulate the amount of light falling on the film or sensor. The first is through Aperture, which is an opening through which light falls. The bigger the hole, the more light is let in. Lenses are set up such that each notch above a certain aperture setting doubles the amount of light coming in, and each notch below as setting halves the amount of light coming in. The aperture numbers are in crazy decimals numbers that make no sense to most of the human race, but they are magic numbers that are actually the denominator of a fraction. Thus 1.8 is actually 1/1.8  and 1.4 is actually 1/1.4.  But regardless 1.8 lets in twice as much light as 1.4, etc.   Since this is in a fraction the higher the number the less light comes in.

The second way of controlling light is through the shutter speed. There is a little shutter that moves up and down and remains in the open state for a specified amount of time. Normally this number also represents the denominator of a fraction of seconds. Thus a shutter speed of 60 is actually 1/60th of a second. While we can move up and down incrementally, the effect of the changes is more gradual than with the aperture. Thus if you want to halve the amount of light that is coming into a 1/60th shutter speed, you move it to 1/120th second shutters speed.  The higher the number the LESS light that comes in. If you camera was and oven and you were baking pictures, the shutter speed is how long you would leave the camera in the oven.

ISO is third in-camera option in regulating light. This does not control how much light gets to the sensor but how sensitive the sensor is to the light. The more sensitive the less light it takes to register the image.

To take great pictures your camera needs a lot of light. Now when I say a lot of light, I do mean a lot of light. The problem is that our eyes are often a horrible judge of the amount of light in any given area. There are some reasons for this. The first is that our eyes adapt fairly well to low lighting. Good enough that we think the low light is normal, that is, until we step out into sunshine. The brain tries to equalize our environment. There is another perceptual error…our viewing of light is on something like an exponential scale. It takes way more than twice the light to make it seem twice as bright. For example, turn on a lamp. put another lamp next to it and turn it on. Did the second lamp make the room twice as bright to you? No. But the room is twice as bright.


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