When we look at the elements of composition, the three that everyone constantly considers are shutter speed, aperture settings and ISO (or ASA in the old days of film). These three factors make up something called the Exposure Triangle.
Readers of the blog have seen this before, in my post about The Future of Photography. The rules of the exposure triangle (such that there are rules in photography…) state that if you want to keep the lighting the same in your shot, as you increase one factor, another must decrease proportionally, while the third is kept the same. What does that mean? Simple – let’s take scenario I encountered when on a photo shoot with some friends touring the waterfalls of South Carolina. While shooting, I saw a perfect scene to demonstrate how this would be manifested.
For our first example, let’s set set up our camera and take a picture of a waterfall. In order to hand hold, and easily compose things, we have the following settings.
- A shutter speed of f 1/250
- An aperture of f 4.5
- And an ISO of 100
Fabulous – but in looking at the photo, we’re not crazy with how the photo looks. Something is off, and we want to change one of our settings to make for a better composition. I’d like to see the same photo but with some blurred water. Now in your own photography it could be something else, like a flower to be sharper throughout the entire depth of the frame, or the background of a portrait to be completely blurred. So, how do we accomplish that? This is where understanding what each factor does to the composition:
Shutter speed
Shutter speed controls how quickly the shutter opens and closes. The higher the setting, the faster the “action” is – so you can freeze something like a speeding bullet, a blade of a moving helicopter, or the wing of a hummingbird.
Aperture
The aperture is the size of the opening on your lens. Think of it like a hose that controls flow rate. You could use a really skinny hose that only lets a teensy bit of water through, or a fire hose that just gushes gallons and gallons. Now, as you open the aperture wider, and let more light in, you also do something called creating a shallow depth of field. And the more shallow your aperture is, the less focused things will be in the foreground and behind your subject.
ISO
The ISO is the noise or sensitivity setting for your camera sensor. This changes how sensitive the sensor is to light hitting it. Lower ISO settings make it more sensitive to light, higher settings make it less sensitive. Back in the days of film, this was done by using films of a certain ASA value (which ironically was referred to as film speed, but I digress…) But the fun thing to consider is that once you inserted film in a camera, you were stuck with that film setting until you finished every frame, so ISO adjustability in digital cameras was a HUGE advancement.
Okay, so now, back to our example photo. Now in our example, we want to make the water more blurred, so we have to slow the shutter down, not speed it up. Okay, so let’s do that:
New shutter speed = 0.5″ (one half second)
So, what’s going to happen? Well, because we are now letting the shutter stay open a LOT longer (0.5 seconds is HUGE, but we need that to really blur water)! As a result, more light is going to hit the sensor, and make it way too over-exposed, so we need to compensate for that by adjusting the other two controlling elements – aperture and ISO. Now in this example, our ISO is already as low as it can go, so our only option is to make our aperture opening much smaller:
- A shutter speed of f 0.5″
- An aperture of f 29.0
- And an ISO of 100
See how we did that? Now, this shot is going to have much more blurred water, and our exposure stays consistent. But, we’ve effectively made the same shot with a different composition!
See how the shutter speed and aperture will change the entire composition? Yes, I blurred the water, which was my primary goal, but look at the log in the foreground. Now it’s a little out of focus due to the shorter depth of field. Pretty fun stuff, eh? I should also mention now that since I slowed the shutter speed to half a second, there was no way I could hand hold that, so I mounted it to a tripod in order to prevent camera shake.
As a reminder, for a strict metadata comparison, that’s what happens when you account for the exposure triangle:
Shot 1
- Shutter speed = 1/125th
- Aperture = f 4.5
- ISO = 100
Shot 2
- Shutter speed = .5 seconds
- Aperture = 29
- ISO = 100
Happy shooting!
Author note: I was going to post this article in response to a question that came to me from Quora. Imagine my surprise when I realized I had never written a post in 10 years on something as fundamental as the Exposure Triangle! It may have been written and lost in the server crash from a few years ago, but thanks to Quora for giving me the reason to re-create it now!
