Hey there! Pesty Laura here again with some more photography 101.
When I first began playing with my camera I really had no idea what I was doing. I knew the sorts of pictures I wanted but I was afraid of breaking my (expensive!) camera. I mostly shot on auto, which is the little green square where the camera basically decides what look you are going for and does it for you. My pictures were ok. Then I took a photography course and in the course of a few months, my photography skills grew in more ways then just knowing my camera, I began to pay attention to things like light, movement and depth.
Shutter speed in a nut shell.
The shutter of your camera is the little device that opens and shuts to let light in, capture the moment and save it to your disk. Its the little 'whoosh' you hear when you press the button. The shutter speed is how fast or slow the shutter is moving. The faster the shutter is moving, the faster its 'capturing' the action and will basically freeze a few milliseconds in time. The slower it is, the more blur you get because its capturing more time and movement. So if you take a picture of someone running with a slow shutter speed, you will get a blur where their legs are moving.
Why do I want a fast shutter speed? You should never allow your shutter speed to go below 1/125. Your body is going to naturally move as you snap a photo and anything under that is EXTREMELY hard to hand hold (meaning you're not using a tri pod) and you will get some blur. An older child or adult that knows they are getting their picture taken and is sitting there smiling can handle 1/125 but a moving baby or toddler that you are chasing around, you really need to be at 1/200 to make sure the blur isn't going to ruin your photos.
Why do I want a slow shutter speed? Sometimes adding a little bit of motion is neat! A twirling skirt, a spinning wheel can all add interest when you slow time down and capture a little movement. Another very neat effect is to mount your camera on a tripod (or even set it on something like a brick wall), have your subject stand PERFECTLY still and photograph at a slow shutter speed with traffic behind them. Your subject will look nice and in focus, with a blur of motion behind them.
Here are a few examples of neat effects with a slow shutter speed:
A hint of motion in her hair and skirt, enough to know she was twirling around.
Water is an awesome thing to photograph with a slow shutter speed.
Shutter speed has effected a lot of my photos in a not so great way. Most of the time, if my photo isn't in focus it isn't that I misfocused its because the shutter speed wasn't fast enough and I caught some blur either from them moving or from camera shake (me pressing the button). If you are seeing blur, check your shutter speed and make sure you are at 1/125 or better. If you are shooting in low light, your camera will need a slower shutter speed in order to get the amount of light needed. Changing your ISO or aperture will allow your shutter speed to get up to where it needs to be in order to capture a crisp, beautiful portrait.
Aperture in a nutshell.
I'm sure there is some fancy, scientific stuff to be said of aperture. And there are plenty of camera manuals and books to tell you all about it. I was never interested in the scientific, I just wanted to know the low down. So here it is. A smaller number is considered a larger aperture because more of your aperture is open to allow light to enter your camera. Most cameras start at 3.5 but some, such as a 50mm can go down to 2.8 or lower. Your aperture range depends on your lens and if your lens can't go down below 3.5, you have to look at other ways to get light into your camera.
A 3.5-4.0 is a normal range for portrait shooting. You are getting enough blur to have a nice portrait. The lower your aperture, the harder it is to really pin point your focus. You have a smaller depth of field that is in focus so it can take practice.
Why would I want a shallow depth of field? When we are talking about shallow depth of field, we are talking about using a large aperture (small number), that has our subject in focus and everything else blurry. This is a traditional portrait. Here is an example.
This is a photo of my daughter at 4 months. You can see her face up to about her front shoulder is in focus. At her chest, you start to go blurry and by the time you are to her diaper and leggings, its a complete blur. This was taken at a 2.8. So you are talking about maybe 6 inches being your depth of field (or range that is in focus). That means if I had accidentally focused on her chest, I probably would have gotten her eyes to look very nice. And the eyes are what you are typically worried about.
Forgive the poor quality of this photo. I took this last November so I've had a year of practice since then. This is a photo of my husband and I can tell, it had a smaller aperture because more of the photo is in focus. Its in focus from my husband to the brown part of the trellis. You can see how six inches can go to several feet. A smaller aperture is going to let in more light, but get more of a photo in focus for you.
Small number = large aperture
A small number will allow in more light, meaning you require less light. So in low light situations, you are going to want a large aperture. However because of your shallow depth of field, your ability to focus correctly on the eyes is crucial.
large number = small aperture.
This aperture requires more light. Most likely you will need to be outside or using some sort of flash. You are going to get a larger depth of field, but for portrait photography, you won't want to go above 5.6 or you will lose the blur that makes your subject pop out.
You can see that light will make you choose between a fast/slow shutter speed and a small/large aperture in order to meter in the middle. Somehow your camera has to get the amount of light it needs to capture the image. As you speed up your shutter speed, your camera needs light so you then have to go to a larger aperture, making it harder to focus correctly. Opening up your aperture will require a slower shutter speed, which can cause blurring of your image. Luckily you probably won't run into these problems unless you are shooting indoors or when it is very overcast or when its just getting too dark to shoot outdoors.
I hope this helped you out a little in understanding shutter speed and aperture. Keep snapping the moments!