Trying to take great photographs without understanding aperture and shutter speed is like playing darts blindfolded; you are just aiming blindly at your target. Aperture and shutter speed are the two most important manual controls on a camera, with ISO being a close third. Being able to shoot in low light, bright light, near, far, fast and slow is all made possible by understanding how aperture and shutter speed interact. This guide introduces, explains and provides some general starting points for using aperture and shutter speed. If you’re looking for more straight-forward advice, check out this simplified system for perfect photography.
Light is king in photography. A photograph’s exposure controls how light or dark the image will be once developed. As you might have guessed, there are three factors that determine exposure: aperture, shutter speed and ISO. We are primarily concerned with the first two, but in certain circumstances ISO can be the difference maker.
Perfect exposure is a result of balancing these three variables, but aperture and shutter speed have a special relationship in that they affect each other directly; changing one immediately affects its balance with the other.
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A Brief Note On ISO
ISO is a measurement of the light sensitivity of your film. You can only change ISO by changing the film (unless you are using a digital camera, which many are). ISO is measure in numbers; 100, 200, 400, 800, etc. The higher the number, the more sensitive the film. A very sensitive film allows you to take very fast pictures. The only downside is that the higher the ISO, the grainier the picture will be. You can’t have your cake and eat it, too . . . unless you master aperture and shutter speed.
If you literally know nothing about how cameras work, this might come as a shock: aperture controls the size of the opening in the lens. Obviously it doesn’t change the physical size of the lens, but it either loosens or constricts an internal mechanism. So the glass piece on the end of your lens is not actually the size of the light-capturing hole; it exists to direct the light towards the aperture. Aperture enthusiasts looking for more details should read this blog post on understanding aperture and manual settings on your DSLR.
The affects of adjusting the aperture are self-explanatory: if you make the hole bigger, more light gets in; if you make the hole smaller, less light gets in. But how does this affect your photograph?
The Focal Ratio
Aperture controls depth of field, as well. The smaller the aperture, the wider the depth of field; the larger the aperture, the narrower the depth of field. Apertures are expressed as “f-stops,” or the “focal ratios.” Mathematically, it is the ratio of the diameter of the aperture to the length of the lens. But all you really need to know is that the smaller the f-stop number, the larger the aperture opening, and vise versa.
There are standardized f-stops that don’t make sense when you first look at them, but they actually relate to each other in a very simple way: f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8.0, and the list goes on.
So how are these numbers related? Anytime you move down a stop (for example, from 1.4 to 2.0; remember, this is considered moving down because the the larger number means a smaller opening), the amount of light that passes through the lens is halved. Almost needless to say, anytime you move up a stop, such as from 4.0 to 2.8, the amount of light doubles. These standardizes stops are referred to as full stops; a truly manual camera will allow you to use half-stops and/or third-stops, as well.
The film of your camera is protected by a window that opens and closes. This is called the shutter. Shutter speed, then, refers to the length of time the shutter stays open. These times are expressed in seconds. Your average high-quality camera will have shutter speed options starting at 30 seconds (for shooting a starry sky) and often exceeding 1/1000 of a second (for capturing a cheetah without blur). If you’ve always wanted to take night photographs, this long exposure photography course can help you master the art.
Interestingly, the same relationship that exists between f-stops exists between shutter speeds. There are standardized shutter speeds, as well; 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, etc. Moving up or down a “stop” in shutter speeds halves or doubles the amount of light reaching the film, respectively. Since this is a matter of doubling or halving time, it is easier to understand than aperture. But by this time you should be able to see how aperture and shutter speed affect each other.
The Art Of Imperfection
In the most general sense, the smaller the f-stop (i.e. the larger the opening), the faster the shutter speed it will require. This is because film gets overexposed so easily. If you’re letting more light in, you have to let it in for a shorter period of time, and vise versa. A tiny aperture will require more time for light to saturate on the film.
The important thing to understand is that there are no perfect settings that will give you perfect pictures every time, in every scenario. That is what makes photography an art. You have to experiment, and often you don’t want a perfect exposure. Imperfect exposures can add mood and intrigue to your photographs (sometimes you want blur, motion, etc., and sometimes you don’t), so the only way to begin to understand how shutter speed and aperture work together is by experimentation.
Still, it’s good to have a place to start. To capture clear, well-exposed photographs on your average, partly-cloudy day, you should start with these aperture and shutter speed pairings:
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