I've discussed this quite a bit here, but have been getting a few emails about it and so I wanted to throw out a little more info.
And (as always), my disclaimer:
I am NOT a professional professional photographer by any stretch of the imagination.
In portrait style photography, it is often the goal to have your subject crisp and in focus, while your background it out of focus.
This effect is created by the aperture setting on your camera.
Think of your camera as a light-proof box.
And in order to capture a photo, light must enter the camera and hit the light sensor inside of it (digital cameras have light sensors, regular cameras have film).
The light that enters your camera comes in through an opening inside your lens, made by a bunch of overlapping metal blades, called an aperture.
That aperture can open and close to varying widths (because the metal blades overlap one another). When the aperture is open as wide as it can possibly go, you can imagine that it lets more light inside your camera (allowing you to work in lower light situations). And so, of course, when the aperture is closed down very small, it lets in very little light (not so good in low light situations).
As you increase the width of your aperture, you decrease how much of your photo can be in focus at any given time (that is why you can have your subject perfectly in focus and your background out of focus).
As you decrease the width of your aperture, you increase how much of your photo can be in focus at any given time (that is why you can have a wild flower right in front of your camera perfectly in focus and have the mountain range ten miles away in perfect focus too).
How much of your photo is in focus is called depth of field (used somewhat interchangeably with the word aperture).
A camera with interchangeable lenses and any camera that will allow you to work in manual settings will allow you to decide how wide you want your aperture (point and shoot cameras will not allow you to do that).
There are numbers, called f-stops that correlate to the width of your aperture. Those numbers typically range from f1 to f22. It's a little confusing, but the the lower the number, the wider your aperture is open. And so, the higher the number, the smaller your aperture.
If your a numbers kind of girl (which I am not), it might make a little more sense to know that an f-stop is written like a fraction. The "f" in the equation being equal to the focal length of your lens, which is then divided by the number you see next to the "f". So if you are shooting with a 50mm lens, and your aperture was f4, the equation would look like this 50/4 (50 divided by 4), which helps to make sense of why the lower the f-stop number, the wider your aperture and the higher the f-stop number, the smaller your aperture.
If your not a numbers kind of a girl - just pretend you never read that last paragraph.
So an f1 would mean that your aperture is wide open, letting in as much light as possible, but only a small portion of your photo will be in focus.
And an f22 would mean that your aperture is closed down very, very small, letting in very little light, but every detail in your photo will be in focus.
In the photo on the left, I set a high aperture (f16), which resulted in everything in my photo being in focus (even the ugly construction in the background). In the photo on the right, I set a pretty low aperture (f2.8) and the result was that Courtney was in focus, Coley was out of focus and so was to distracting background.
Another good thing to note is that the further your subject is away from the background - the more the background will be out of focus.
How wide your aperture will open up is directly correlated to the quality (and unfortunately, the cost) of your lens. A lens that will open up all the way to f1 is going to cost quite a bit more than a lens that will only open up to an f4.
Most of the lenses that come in a "kit" (meaning that when you buy the body of your camera, it comes with a lens or two), don't go down any lower than f3.5, and unfortunately, a 3.5 aperture will not allow you to work in low light situations, will not usually allow you to get a really good blur to your backgrounds and will limit the quality of your photos.
I used to have three lenses, none of which would go any lower than a f3.5. When I got them, I loved them. When I learned more about photography and tried a better quality lens, I got rid of all of them.
I have three lenses now too (just got a brand new one), and all of them will go down to an f2.8 (one of them will even go down to a f1.4).
The difference between an f3.5 and an f2.8 is enormous. And at this point in time, I wouldn't get a lens that didn't drop down to at least a f2.8 (even if it meant that I had to wait & save until I had enough money to buy it - which is the case with the lens I just got).
Right now, the three lenses I have are:
- Tamron 28-75mm f2.8
- Canon 50mm f1.4
- And introducing my new baby, Canon 16-35mm f2.8
I think that the quality of your lens in most cases, is actually more important than the quality of your camera body.
That is why, right now, I really want a new camera body (I shoot with a Canon 20D - which don't get me wrong, is a fabulous camera, but I'd still love to upgrade), but I'm not going to get a new camera body, because I don't have a money tree in the backyard.
And in knowing that the quality of my photos is more influenced by the quality of my lenses than the quality of my camera, I'm investing my money in lenses.
Ok, and now...how do you change your aperture settings?
If you've got a manual camera, there should be a setting on the main dial that says "AP" or "AV" or "A". That setting is called aperture priority (that's the setting I work in 90% of the time). In that setting, I decide what I want my aperture to be and my camera automatically sets my shutter speed for me (it's that easy).
So if I'm shooting a portrait of a person, I'd love to be at f2.8. If I am working indoors, under poor lighting conditions, I may drop it to an f1.4. If I am shooting a group of people outdoors, I might start at f8 and see how it looks (remember, if your aperture number is low, only a portion of your photo can be in focus at any given time, so shooting at a low aperture number with a group of people would mean that most of those people would be out of focus). And if I'm shooting landscapes, my aperture is usually going to be set to a high number so that everything in my photo can be in focus.
Aperture is my favorite thing about photography because I think that I can work really creatively with it to tell a story and so, I find that although I have some guidelines that I follow for where I set my aperture given a particular subject, I don't abide by any strict rules (hard to be creative with strict rules).