Exposure – The Basic Element of Learning Photography

December 2, 2020December 2, 2020 Tom Marvin

So you want to be a photographer. Maybe you’ve been a phone-tographer and you have your first real camera and maybe your photos aren’t turning out like you expected them to.

The first thing you have to master, as a new photographer, is exposure. Exposure is basically how light or dark an image is. Capturing the perfect amount of light for a great exposure can be tricky.

When you take photos with your phone, there are no dials to twist to make adjustments. You just push the button and your phone does it all for you.

Or maybe you’ve had your camera for awhile, but you’ve kept it in the Program or P mode. In this mode, the camera decides what aperture (or f-stop) and shutter speed to be used based on the amount of light in the scene you want to photograph.

One time I was photographing a high school basketball game. The school’s photography instructor was also taking photos at the game. During the first quarter the photo teacher came to me and asked me if I could tell her why her camera was broken. All of her photos were blurry and she couldn’t figure out why.

I took a quick glance at the back of her camera and told her it was because she was using the Program mode on her camera.

The camera was deciding that inside the gym, she needed a really slow shutter speed to get a good exposure. The blur in her photos wasn’t because of a broken camera, it was because she didn’t have the camera settings needed to take fast action sports photos. The blur was motion blur from the fast-paced basketball game being photographed using an extremely slow shutter speed. While it had a lot of motion blur, the camera was perfectly exposing that motion blur.

To set the exposure on a digital or film camera, the photographer must understand and set:

ISO
Shutter speed
aperture

Shutter speed, aperture and ISO (or film speed if your are shooting with film) are the three things you can adjust on a camera to effect exposure.

If you put your camera in manual mode, it doesn’t mean that you have to manually focus the lens. What it does mean is you, as the photographer, have complete control over all three legs of exposure (ISO, shutter speed and aperture). Manual mode is the only one where the photographer has complete control over exposure.

But exposure isn’t just a math problem with just one correct answer.

It’s more like a recipe. Cooking, like photography, allows great cooks to make the same dish with a variety of flavors. A photographer selects his exposure settings to give his photos a unique flavor. If you need to take photos at a basketball game, like my photography instructor friend, then your shutter speed will be your priority. You will need to come up with an exposure recipe that allows you a fast shutter speed to stop the action.

Exposure boils down the the combination of shutter speed, aperture and ISO settings that allow the correct amount of light hit the image sensor (or film) to create a photograph.

To help you understand how ISO, shutter speed and aperture work, it may be helpful to think of filling buckets with water instead of how much light you are letting into the camera.

The perfect exposure is the combination of ISO, shutter speed and aperture that allow the right about of light onto the sensor.

Changing the ISO changes the amount of light needed to create the exposure.

In our example of filling buckets of water, the changing the size of the bucket is like changing the ISO.

**Here are photos of an old film camera with the back of the camera open so you can see the size of the aperture. The top photo shows an aperture of f2.8. The bottom photo if f16.**

If you compare ISO 100, ISO 1000 and ISO 8000, the larger the ISO number the less light you need to get a good exposure. Without adding any additional light to the exposure, you can use ISO 100 outside during the day to get a good exposure. You can use ISO 1000 to get a good exposure inside. You may need to go all the way to ISO 8000 to get good photos in a dimly light room and still be able to use a shutter speed to able to stop action.

In our filling water buckets example, ISO 100 would be like having to fill a five gallon bucket with water. ISO 1000 would be like filling a mop bucket and ISO 8000 would be like having to fill a child’s water cup. Just like ISO 8000 needs a fraction of the amount of light as ISO 100, a child’s water glass needs a fraction of the amount of water to fill it compared to a five-gallon bucket.

When we take about the aperture of a lens, we are talking about how much light can get though the aperture to the sensor. The smaller the aperture number, the larger the opening is to allow light into the camera.

At right are two photos of a film camera with the back open so you can see the size of the aperture. Notice how large f2.8 looks compared to f16. The smaller the aperture number, the larger the lens opening.

Using our water example, think of apertures like this:

f2.8 is like using a fire hose
f8 is like using a garden hose
f16 is like using plastic tubing similar to what you would use in a fish tank.

Shutter speed is the amount of time you allow light to go though the aperture. When you change the shutter speed number on your camera, it shows you whole numbers.

The numbers can vary from say 2 all the way up to 8000. These are actually fractions. The number 2 is ½ a second. 40 would be 1/40 of a second. 100 is 1/100 of a second. And 1000 is 1/1000 of a second.

Because they are fractions, the smaller the number, the longer the shutter is open and allowing light through the aperture.

**The in-camera light meter shows a correct exposure.**

How can you tell when you have the right combination of ISO, shutter speed and aperture? Simple, almost all cameras, both digital and film, have a light meter in them and you can view it by looking though the view finder. Sometimes it’s at the bottom of the viewfinder and sometimes it’s on one side.

As you make adjustments to ISO, shutter speed and aperture, you will notice your exposure moves back and forth on the light meter. If the exposure mark is under a negative number, the photo will be under exposed (too dark). If the exposure mark is under a positive number, the photo will be over exposed (too light). Make adjustments to your ISO, shutter speed and aperture until the exposure make is under the arrow in the center of the light meter.

See in the photo at top right, the light meter goes from -3 to +3. The center of the light meter has an arrow shaped icon pointing down. This is what your light meter thinks is the perfect exposure.