Within every single lens, whether it be a DSLR lens or a point and shoot lens, like the one on this camera, there is something that is called an aperture. Now what the aperture is, is essentially a circle that controls how much light comes through the glass and passes through into the sensor behind. I am going to draw exactly what that aperture looks like, just to give you a basic idea.
This is the bottom portion of your lens. Generally they are made up of blades. It would look something like this. The light is going to pass through this circular area here, so you can control that area to control your exposure, essentially.
Maximum aperture is how open that space can get. Lenses like this, higher end lenses, will have that space be able to open very, very wide. That means that more light will be able to come in. What exactly happen though, when you open that up or close it down to a tiny little hole?
Well, I will show you. Let's just say, for argument's sake, this is about the equivalent of an aperture of f2.8, which is fairly open, and this is equivalent of an aperture that's f16. Keep in mind that this is the center hole that is letting light into your sensor.
At f2.8 you're going to be able to get a much faster shutter speed than f16, just because the amount of light coming in is much higher, however, what that affects is something called depth of field.
Depth of field is a really simple concept. When your aperture is very open, maxed out, letting the most light in, you are going to have a very shallow depth of field.
What shallow depth of field means, is literally, whatever you are focused on, whatever point in the frame you are focused on, everything beyond that point, or in front of that point is going to fall out of focus, and you're going to isolate that one subject. Now this works really well on some photos, and it doesn't for others, so that's something to keep in mind.
For example, if I'm taking a picture, say that there is a guy standing here, there is a tree behind him, maybe there is fire hydrant right here, and a bird flying right there. If I'm shooting from right here with my camera, and I have it at f2.8, only this guy is going to be in focus, however if I make my f stop, my aperture, smaller, I can get everything in the frame into focus, within reason.
So again, if you're shooting something, let's say, like a basketball game, you may want a somewhat shallow depth of field so that you can isolate the players in the frame, and the crowd kind of falls out of focus.
Say you are shooting something like a landscape. You're going to want to have those things in the frame in focus. In fact, probably the world's most famous photographer, Ansel Adams, was known to shoot at f64. He even had a crew of his homeys, who were all these photo buddies that shot these brilliant landscapes, and they are called the f64 club, meaning that they would only shoot with lenses stopped all the way down to f64, which is basically a pin sized opening in your lens. The reason that they did this was because all of their photographs, or most of them, were tripod mounted, and they were are these gigantic landscapes; and he and his cohorts wanted everything in that landscape to be perfectly sharp and in focus.
The nice thing about lenses that open up really wide and have a really good maximum aperture like f1.8 or f1.4, or f2, or f2.8, is that you can do a lot better in low light. Obviously, you are going to sacrifice depth of field, and you are going to have a shallow depth of field in low light, but you will be able to shoot much better.
Now if I was going to a concert and I was going to shoot in f64 inside the venue, I would be totally out of luck. With a lens like this, if I had it stopped onto f1.8, I'd have a much easier time. The reason I would have a much easier time is simply because there is more light being allowed into the lens. Because it is a low light environment, you want to maximize that amount of light to keep your shutter speed fast enough that your subject isn't blurry.
So these are the basics and some tips just to help you wrap your head around this whole idea of aperture.