Today we’re going to discuss aperture. Not the popular Apple software product for cataloging and editing photos.
Your camera’s aperture controls how much light is let into the camera, but also and more importantly how much of your image will be in focus. But first, covering how aperture is noted.
You will encounter the aperture noted in terms of f-stops, or more commonly f/2.8. Unlike many things, the smaller the f number on a lens, the wider the aperture is. It is based on a logarithmic equation, seen below.
The f-number f/#, often notated as N, is given by the above equation. Where f is the focal length, and D is the diameter of the entrance pupil. By convention, “f/#” is treated as a single symbol, and specific values of f/# are written by replacing the number sign with the value. For example, if the focal length is 16 times the pupil diameter, the f-number is f/16, or N = 16. The greater the f-number, the less light per unit area reaches the image plane of the system; the amount of light transmitted to the film (or sensor) decreases with the f-number squared. Doubling the f-number increases the necessary exposure time by a factor of four. Equation and following text is care of Wikipedia.
But enough math…you’re probably wanting something more concrete and practical. So let’s use my handy manual focus 50mm lens for that. The lens is rated at f/1.4, it is the lens with the widest aperture that I own.
To the left is the lens wide open (f/1.4) as you can see, it will let in a lot of light, to the right is the lens at f/16.
So while having the lens wide open lets in a lot of light, which is great for dark places, there is a downside, you loose how much of the image will be in focus, this is called Depth of Field (DoF).
How does this translate into your photos.
Let’s call in my friend Jay for a bit.
(50mm ~ f/1.8 ~ 1/50″ ~ ISO-1600)
As you can see, very little of the image is in focus, pretty much the only thing in focus is the “Hold” tag on him. Opening the aperture can create some pretty dynamic effects and can really help make the subject pop out of the rest of the frame.
So now we’ve had it wide open let’s close it all the way down. Here’s one of my favourite shots, in fact it’s the one used in the banner for my website and this blog, taken using the same lens as the above image (just to be fair).
(50mm ~ f/22 ~ 1/60″ ~ ISO-200)
As you can see, the image from the CN Tower in the background to the houses in the foreground everything is sharp and in focus.
How do you apply this to your photography, well again it’s all about your subject matter. When it comes to portrait work you want your subject(s) to be the only thing in focus in the frame, so you want a shallow depth of field, for group shots, a deeper depth of field so that poor Uncle Bill isn’t out of focus. When it comes to landscapes, you want all the details to be in focus so closing the aperture is desired.
Tags: aperture, Camera, depth of field, Photography