BACK TO THE BASICS
Are you just starting out with photography? Or maybe you've had some interest in it, but are struggling to take your photography to that next level. For me, a huge shift took place in my own photography journey when I understood the basics of how cameras work. It enabled me to begin to shoot in manual mode on my camera, which changed everything. Finally I was in control of my images. It was freeing to know exactly how to manipulate my camera to make it do what I wanted it to do. And my images became much stronger and more consistent. That's when you move from simply operating a nice camera and hoping for the best, to becoming the artist behind the camera. You're in control of your images and the camera now becomes the amazing tool you use to get there.
THE EXPOSURE TRIANGLE
It doesn't matter what type of camera you're using, they all follow the same basic principles of the exposure triangle: aperture, shutter speed, and ISO. I'm going to go through each of these individually and how they interact to hopefully give you a better understanding of how things work. Confused already? Don't worry, I was too in the beginning. Stick with me and let's see if it makes sense.
IT'S ALL ABOUT LIGHT
Basically it's all about light. The camera needs a certain amount of light to properly expose an image. You can let that light in through one of three ways: aperture, shutter speed, or ISO. I'll go through what each of these means and then we'll talk about how they interact and why you would choose to change one over the other.
This is how wide the shutter opens up. The wider (or more open) your aperture, the more light is allowed to come in. The smaller (or narrower) your aperture, the less light is allowed. This is noted by f-stops. They are backwards from what they seem (confusing, I know): f/2 = very wide, f/11 = very narrow. The size that your shutter can open up will vary depending on the lens. Some open up to f1.2, while others open up only to f4.
2. SHUTTER SPEED
How fast the shutter opens and closes. Shutter speed is measured in seconds and fractions of seconds. A shutter speed of 1" means your shutter is open for 1 second of time, while a speed of 1/100 means your shutter is open for "one one-hundredth of a second".
Sensitivity of the image sensor (for digital cameras). This term comes from film cameras where ISO referred to the sensitivity of the type of film being used. The lower your ISO, the more sensitive your sensor is to light; and the higher your ISO, the less sensitive it is to the available light. The ISO on your camera most likely starts at ISO 100 and increases incrementally.
THEY ARE ALL CONNECTED
For any given real world scenario, there will always be a certain amount of light that needs to go into your camera to properly expose an image. If you change one of these three basic camera elements, the other two must change in response to maintain that proper amount of light. Let's look at a few examples, assuming you're photographing outside, with plenty of available light.
1. If you open your aperture very wide, it's going to let in more light. Therefore, your shutter speed will need to be faster, so it lets less light in. Otherwise your image will be overexposed.
2. Let's say you want your aperture to be very small. It's going to let less light in than the previous example, so your shutter speed will have to be slower so that it has time to let more light in.
Let's add ISO into the equation. As a rule of thumb, you generally want your ISO to be as low as possible. For the above situations, if I had plenty of light to work with I would set my ISO at 300 or less and just leave it there. That way all I have to think about is adjusting my shutter speed and aperture. However, there will be times when you have less available light - as the sun is going down or a lower light indoor situation. During these times, you may need to raise your ISO. You may also have to keep your aperture very wide and slow down your shutter speed. See how when you change one factor, they all change?
WHAT DIFFERENCE DOES IT MAKE
You may be wondering why it would even matter which one you change. That's where you move from just operating a nice camera to actually becoming an artist and taking control of your images. There are lots of creative choices to be made that will completely change the outcome of your image depending on which of these three things you adjust. This is why it's so important to be able to move beyond shooting in auto mode on your camera. You will have so much more freedom to shoot what you want to shoot! Let's go through some examples to see the creative choices you make when changing each of these.
A wide aperture creates a shallow depth of field. Great for portraits and blurry backgrounds. Notice in the image below how the trees and the table cloth are blurry and the only area in focus is right around her face? That's only achieved through having a wide open aperture.
In the image below, notice that the leaves are all blurry, bringing focus just to her. Again, this is because the aperture is wide open. In this scenario I was working with less light, so my shutter speed is a bit slower and my ISO is higher, but I knew I wanted to keep my aperture as wide open as possible.
One more example of using a wide aperture to focus on one small area of the image - in this case on the blueberries in her hand.
Now let's talk a bit about the times when you may want to use a narrow aperture. These are times when you want everything in your image in focus. In landscape photography, this is usually the case as you are photographing a large area and most likely want it all to be sharp.
Here are a few taken from our honeymoon to Patagonia. Notice that everything from the road in the front to the mountains behind are all in focus. This is only done through using a narrow aperture.
Note in the above photo that lighting was already limited and I knew I wanted keep a more narrow aperture (allowing for even less light to come in). As a result, my shutter speed needed to be slower to allow more time for light to come in and my ISO needed to be higher.
Let's talk about what happens when you change your shutter speed. When your subject is moving, you will need to have a faster shutter speed, otherwise the image will be blurry. It can also appear blurry if your hand shakes or moves at all when taking the photo.
In this photo, the shutter speed was extremely SLOW - 4 seconds long. It gave the effect of motion, which is sometimes desirable and sometimes not. Slow shutter speeds are often used for images at night of a cityscape for example. If you have a tripod, you can set your camera up and use a slow shutter speed to capture lights, stars, etc. You'll need a tripod or some sort of support though because any motion of your hands holding the camera even for just a fraction of a second will cause the image to be blurry.
Note that because my shutter speed was SO slow, my aperture needed to be very small to let less light in and my ISO very low; otherwise my image would have been overexposed.
Below is an example of when you may want to use a FAST shutter speed. If your subject is moving quickly (as is often the case with children) and you want them to be sharp and in focus, you'll probably want to keep your shutter speed at least 1/100 or above.
It's always best to use the lowest ISO possible. There will be situations, however, where you just don't have enough light. You aperture may be as wide as it can go and your shutter speed as slow as you want it to go and you still don't have enough light. This is when you will have to bump your ISO up higher. The reason you want adjust this setting last is because using too much ISO will result in grain in your images. The dark areas will have some 'noise' to them. The amount of ISO you can use will depend on your camera. Some camera's are better than others and can be bumped up much higher.
The photo below is an example of where I had no other choice but to bump up my ISO quite high. The photoshoot was taken on a rainy day in a darkly lit nursery. My aperture was as wide as it will go and my shutter speed was 1/40 (just high enough to avoid hand shake), the only thing I could do was raise my ISO. My camera handles ISO very well and you can still hardly see any noise here. But just know that on most cameras when you start to get above ISO 1000, you are going to start seeing some noise and grain.