Today in TechPhotography Tips: What is aperture?
Aperture is perhaps the most important — and also the most confusing — photographic concept to grasp. Mastering the use of aperture opens up a range of artistic possibilities and brings your photography to the next level. First, though, you have to wrap your head around the idea and understand the relationship between aperture, shutter speed, and depth of field.
Aper-what?
Aperture is the term for the opening in the lens that controls how much light reaches your camera's film or sensor. The aperture functions much like the pupil of your eye, which gets smaller or larger to let in more or less light. The aperture in a camera is a diaphragm consisting of a number of blades that open and close to make an effectively circular hole through which light passes.
Size matters
The reason aperture is important and the reason it needs to be adjustable is that size matters. Size matters because light matters — if every single picture you took occurred in the same environment with the exact same lighting conditions, you could get away with a fixed aperture. But you probably want to take pictures in all sorts of light, from the soft candlelight of a birthday party to the bright sunlight of a beach on a sunny day. And you probably want to photograph all sorts of things, from an unmoving landmark to your frenetic puppy.
Think of it like filling a bowl of water from the faucet. If you turn on the faucet just a little, the bowl fills slowly. If you turn on the faucet full blast, you'll fill up the bowl in no time. That's exactly how aperture relates to shutter speed — a larger aperture means more light gets in quickly, which in turn means you can use a faster shutter speed.
Okay, so what's with the F numbers?
Aperture is actually written as a number, preceded by "f/". The F stands for focal length, and the number is a ratio, which we get by dividing the lens focal length by the diameter of the hole.
For example, say you have a lens with a 55mm focal length. A small aperture such as 3mm would be written as f/16, because 50 divided by 3 is roughly 16. This is why a smaller number after the f/ means a larger aperture and vice versa. It's confusing, but just remember: A bigger number equals a smaller hole. Each f/number represents approximately a doubling (or halving) of the one on either side, so an f/8 aperture lets in twice as much light as f/16.
Aperture and depth of field
Depth of field refers to the amount of your photograph that is in focus. In a picture with a large depth of field, something close to the camera will be as much in focus as something far away. A photograph with a small (or narrow) depth of field will have some portion of the image in focus, but the rest will be blurred. You can see this in the photo of the dog at the beginning of this post; the area around the dog is in focus, but the objects closer to and farther away from the camera are blurred.
What does depth of field have to do with aperture? The physics behind it can get pretty confusing, but here's what you need to know: A smaller aperture allows more of the resulting image to be in focus (a larger depth of field), while a larger aperture gives you a narrower depth of field. Having a large depth of field is important when you're photographing landscapes, for example, or a scene where there's a significant amount of distance between subjects you want to keep in focus. A small depth of field lends beautiful bokeh to portraits and other photographs where you want your viewer's attention focused on one area of the image.
Aperture is just one tool in the photographer's arsenal, but understanding how it works is key to moving your photos from "snapshots" to "art." As with all photographic techniques, keep experimenting, and keep practicing!
[Image credits: K. Gray, Cbuckley]
Post by Katherine Gray
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