What is Aperture-
The aperture or “f stop” is what creates those blurry backgrounds people often ask about. Changing your aperture affects that amount of light in your image. The lower the number, the more light is brought in. The higher the number, the less light. Therefore, if you do a lot of indoor shooting, it is nice to have a lens with a lower aperture such as f1.8.
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Lower number aperture = more light and a blurrier background
Higher number aperture = less light and a sharper background
You can visualize the way the aperture works like this:
The type of lens you use is a big factor as to what aperture you can use. You will find that kit lens (most likely the one that came with your camera if you bought a set) do not have a very low aperture. This makes it very difficult to get proper exposure in low light situations such as indoors. And with a higher aperture, you are less likely to get a blurry background which is something you probably want. You are lucky though because both Nikon and Canon sell a 50mm 1.8 prime lens that is fairly inexpensive. I highly suggest this lens if you are learning manual mode.
Shooting wide open means that your aperture is set to the lowest number your lens will go. If I am shooting wide open I will probably only have one eye in focus but will have a nice blurry background. It is possible to get both eyes in focus but you would have to make sure you are on the same plane as your subject (getting down on their level) and your camera would have to be parallel to your subject’s eyes. Cautions when shooting wide open or at the widest aperture, is that it’s too easy to miss focus.
The higher the number the more your picture will be in focus. So if you are shooting people and only want them to be in focus you would set your aperture to be at least the same number as there are people in the photo. If I am taking pictures of my kids (all 4 of them) I would want my aperture to be set to at least f4.0. I prefer a blurrier background so I would probably lower the aperture to about f3.5 and use my shutter speed to get proper exposure. The more people in the shot the larger the aperture number. The more you practice and work with your camera you will find a comfortable aperture where you can get everyone in focus and still get those dreamy blurry backgrounds. Also when shooting landscapes you would want your aperture number to be a lot higher so that the majority of the picture is in focus.
I want you to take photos with both the largest and the smallest aperture sizes your lens has.
Pushing your skillset-
I know many photographers that will shoot a large group of people at a low aperture. To do this they spend a little more time setting up the shot. They have to make sure that everyone is in a straight line and that their toes are all on the same “focal plane”. I have found that it isn’t hard to do this when working with adults who can hold a pose for a couple of minutes but for kids it is not worth the frustration.
A low number/aperture only has a small part of your photo in focus and then gets blurrier as you go out from the focal point creating those dreamy backgrounds.
Aperture is just one part of the exposure triangle. Check out Understanding ISO to keep learning and master your camera.