Introduction to Aperture in Digital Photography
What is Aperture?
Put most simply – Aperture is ‘the opening in the lens.’
When you hit the shutter release button of your camera a hole opens up that allows your cameras image sensor to catch a glimpse of the scene you’re wanting to capture. The aperture that you set impacts the size of that hole. The larger the hole the more light that gets in – the smaller the hole the less light.
Aperture is measured in ‘f-stops’.
You’ll often see them referred to here at Digital Photography School as f/number – for example f/2.8, f/4, f/5.6,f/8,f/22 etc. Moving from one f-stop to the next doubles or halves the size of the amount of opening in your lens (and the amount of light getting through). Keep in mind that a change in shutter speed from one stop to the next doubles or halves the amount of light that gets in also – this means if you increase one and decrease the other you let the same amount of light in – very handy to keep in mind).
One thing that causes a lot of new photographers confusion is that large apertures (where lots of light gets through) are given f/stop smaller numbers and smaller apertures (where less light gets through) have larger f-stop numbers. So f/2.8 is in fact a much larger aperture than f/22. It seems the wrong way around when you first hear it but you’ll get the hang of it.
Depth of Field and Aperture
There are a number of results of changing the aperture of your shots that you’ll want to keep in mind as you consider your setting but the most noticeable one will be the depth of field that your shot will have.
Depth of Field (DOF) is that amount of your shot that will be in focus. Large depth of fieldmeans that most of your image will be in focus whether it’s close to your camera or far away. For example the landscape shot above has an aperture of f/16 and the result is that both the mountain in the background and the boats in the foreground remain in focus.
Small (or shallow) depth of field means that only part of the image will be in focus and the rest will be fuzzy (like in the portrait at the top of this post. You’ll see in it that the subjects eyes are in focus but the background is blurred. Even her hair which is only a little behind her eyes is blurred. This is a very shallow depth of field and was taken with an aperture of f1.8).
Similarly this creative birth announcement image was shot at f1.8 and again you see the shallow depth of field with the ultrasound in focus but everything else blurred.
Here’s one more example with an even wider aperture of f1.2 that leaves the guitar in focus but everything else blurred.
Aperture has a big impact upon depth of field. Large aperture (remember it’s a smaller number) will decrease depth of field while small aperture (larger numbers) will give you larger depth of field.
It can be a little confusing at first but the way I remember it is that small numbers mean small DOF and large numbers mean large DOF.
Let me illustrate this with two pictures I took earlier this week in my garden of two flowers.
The first picture on the left was taken with an aperture of f/22 and the second one was taken with an aperture of f/2.8. The difference is quite obvious. The f/22 picture has both the flower and the bud in focus and you’re able to make out the shape of the fence and leaves in the background.
The f/2.8 shot on the right has the left flower in focus (or parts of it) but the depth of field is very shallow and the background is thrown out of focus and the bud to the right of the flower is also less in focus due to it being slightly further away from the camera when the shot was taken.
The best way to get your head around aperture is to get your camera out and do some experimenting. Go outside and find a spot where you’ve got items close to you as well as far away and take a series of shots with different aperture settings from the smallest setting to the largest. You’ll quickly see the impact that it can have and the usefulness of being able to control aperture.
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