What is Aperture?
Aperture is essentially a small opening that lets light into your camera's sensor. By changing the aperture you are controlling how wide or small that opening is, and therefore how much light is let into the camera. The size of the opening is measured in F-stops - the smaller the opening, the larger the F-stop number. So, a small number like F2.8 is a large opening, and F16 is a small opening. (it seems like it should be the other way round I know!)
What does that actually do?
The main reason for changing aperture when getting more creative with your photos is to control your depth of field. Depth of field is simply how much of the scene is in sharp focus. For example, in a landscape photo, you want as much of the photo to be in sharp focus as possible. However, when taking a portrait photo (or some other situation where you want the main subject to stand out) you will probably want the background to be blurred but your subject in sharp focus.
What F number should I use?
If you want all of the scene to be in focus, then use a high F number, e.g F8
If you want the background blurred, then you use a small F number e.g F2.8
What else affects the depth of field?
How close you are to your subject and how far away the subject is from the background. The further away the subject is from the background, the more blur there will be.
Here are some photos I've taken to show you how aperture affects your photograph. (I'm using good ol' Winnie the Pooh for this demonstration as there is no way my three year will sit in the same spot long enough for me to take these photos) Winnie is always in focus, it's the difference to the background you should be looking at - especially where you can start to see the blur. I'm in the same position for each one, as is the bear.
And one more example side by side - the one on the left was taken at 2.8 , and the one on the right at 7.1
If you haven't played around with your aperture settings before, get outside with your camera and do what I have done here - focus on a stationary object and move through your aperture range, keeping your focus on the object, and see how your final images come out. (Make sure you and your object stay in the same places for this) Next, try moving yourself closer and further away, or use the zoom, and see what changes this makes. Now, move your object further away from the background and see what that does. The idea is to get to know how each aperture setting affects the depth the field, and how both your and your subjects position can also affect this.
So, next time you are photographing your kids, you will hopefully have a pretty good idea of the aperture you will need to set to get your creative depth of field for that particular photo!
I hope this helps those of you that haven't yet ventured out of Auto Mode yet but if you have any questions, feel free to post them in the comments below..
Other posts you might like:
How to get a blurred background
How to Photograph Children: Camera Settings
A quick tutorial on camera exposure