In it’s simplest form, the aperture in a camera lens is the size of the hole in the lens that allows light of varying amounts to pass through the lens to hit the sensor in a camera body. You can think of a lenses aperture similar to a person’s iris (the coloured part of an eye). When you are outside and it is really bright out, your iris adjusts by making your pupil smaller to let less light into the back of your eye. When you are in a dark movie theatre on the other hand, your iris adjusts to make your pupil in the centre of your eye much larger to let in as much light as possible so that you have the best chance of seeing in the dark. Now take that information, but replace a person’s iris with a lenses aperture and you will quickly understand how an aperture works.
What is a F-Stop?
The aperture (or the small blades that form the lens’s aperture) are always adjusted using something called f-stops. f-stops typically start around f-1.2, and go all the way up to around f-30 or f-40.
So as an example, if you have a lens that opens up to f-1.4 as an aperture setting, this means that it is opening up very wide and is letting in a large amount of light through the lens to hit the camera’s sensor. On the other hand, if you have a lenses that only opens up to f-3.5 or so, that means that there is less light going through the lens and hitting the camera’s sensor.
If you are currently using an entry level SLR camera, most likely it came with what is known as a “kit lens”. Kit lenses are inexpensive lenses that typically don’t open up very wide when it comes to their aperture. On the flip side of things, if you spend more money on a “professional” lens like the Nikkor 50mm 1.8 or 1.4 lenses, you will have the ability to let more light through the lens which is referred to as being a “fast lens”.
One thing to keep in mind is that the wider the aperture is able to go on a lens, the more expensive it tends to be. This is because when lenses let it more light, the lens requires a larger aperture and physically more glass to accommodate.
Why change the aperture?
There are two very specific reasons why you would want to change the aperture setting on a camera. The first reason, which I have already mentioned, is to allow more light through the lens to hit the sensor on the camera. The second reason is a much more stylistic choice. The easiest way to remember it is that the more open an aperture setting is on a lens, the more blurred the background will be behind you or your subject. And on the opposite side of things, if you close down your aperture to a very high number, say f-20 or f-30, the majority of your scene or subject will be in focus.
The “depth-of-field” is a fancy term to describe how much of a photo is actually in focus. For a quick example, in the linked video, I am using an f-2.8 lens behind the camera. For this series of videos I am using this lens at it’s maximum aperture of f-2.8 so that I can be seperated from the background by having the background out of focus.
On the other hand, you may require a really high f-stop for something like product photography. For product photography, photographers typically want the product to be fully in focus. If were to take a photo with a wide open aperture of a product, where you focused on the product would be in focus, but everything else would have varying levels of being out of focus.
A lenses “Sweet Spot”
One last thing to keep in mind. With a few exceptions, the majority of lenses are sharpest (and therefore give the highest quality results) around the middle of their f-stop settings. If you are using a kit lens for example, if it goes from f-3.5 down to f-20 or so, it may be a good idea to start shooting at around f-8 because that is when your lens is typically sharpest and go from there.
If you take away only one thing from this article, just remember that a small f-stop number will actually let in more light into your camera. A lot of people starting out with photography will get this point mixed up and reverse it (since that would seem more logical!)
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