Exposure: The beginning of a great photo
Sill Level: Beginner
Getting a proper exposure is at the heart of all photography. I will now attempt to explain it in the simplest terms possible.
You camera has a sensor.
This sensor collects light. Too much light and the image is bright or “overexposed.” Not enough light and your image is dark or “underexposed.”
There are 3 main elements that determine your exposure: aperture, shutter speed, and ISO.
The aperture is just an adjustable hole inside your lens that lets in light.
The bigger the hole, the more light it can let in. The smaller the hole, the less light it can let in.
Aperture is measured in f-stops. This indicates the size of the hole. Though it seems backwards, a lower number means a bigger hole. A higher number means a smaller hole.
Your lens will be rated with its maximum aperture. So if it is a “17-55mm f/4 lens”—that means f/4 is the biggest hole it can make. Most lenses can go to f/22, which would be the smallest hole it can make.
A “fast lens” is one that has a very large maximum aperture. These lenses have an f-stop of 2.8 or lower. They are great for doing photography in low light.
A large aperture (low f-stop number) can also give you shallow depth of field. This allows you to make your background blurry to better isolate your subjects.
This is a very desirable thing for many photographers, so they try to get the fastest lens they can.
Shutter speed is how long your sensor is exposed to light. Think of two sliding doors in front of the sensor. They open, let in light, and then close. A fast shutter speed lets in very little light. A slow shutter speed lets in a lot of light.
Shutter speed is measured in seconds. A fast shutter speed will be a fractional value, like 1/500th of a second. A slow shutter speed can be entire seconds.
Your camera might display fractions as just the bottom number in the fraction. So 1/500th would just show as 500. Whole seconds will have a double quotation mark after. So 5 seconds will appear as 5”.
Faster shutter speeds let in less light, but will allow you to freeze action.
Slower shutter speeds let in more light, allowing you to take images in darker environments. With a long enough exposure, you can make night look like day.
With slow shutter speeds you risk your image blurring due to your hands shaking the camera or movement of the subjects in your photos. So if you do a long exposure, you will almost certainly need a very still subject and a tripod.
There is a formula for keeping camera shake from blurring your photo. You just put 1 over the length of your lens. So if your lens is 50mm, you need a shutter speed of 1/50th or faster. Note: This will not stop blurring due to your subject moving.
ISO is the amplification of your sensor. Similar to the volume knob on your radio, ISO amplifies the sensitivity of the sensor so you can increase your shutter speed or make your aperture smaller. It makes the light “louder.” However, this can come at a cost. The more you amplify the sensor, the more noise will show up in your image.
Some cameras can go to a very high ISO and have very little noise. These cameras are usually frickin’ expensive. As technology advances, cheaper cameras get better and have less noise at higher ISOs.
Getting the Balance
A proper exposure requires balancing aperture, shutter speed, and ISO to get your desired result.
To get shallow depth of field you’ll need a large aperture. So you make your f-stop the lowest number possible. But that lets in a lot of light, so you need a fast shutter speed to balance it out.
To take a long exposure, your shutter speed will now let in a ton of light. To keep from overexposing you may need to make your aperture very small so the image does not overexpose.
If it is darker and things are moving, you’ll need a fast shutter speed and a large aperture. But you can’t get a fast enough shutter speed to avoid blur. So you raise your ISO to amplify the light, allow you to get the proper exposure, and keep your subjects from blurring. Yes, it will cause your image to have some noise, but it is a worthy compromise to get the image you desire.
Photography is often about making compromises. Sacrificing a little bit of quality in one area to create the intended effect with a proper exposure. Learning this balancing act can take years to truly master and in further posts I will go deeper into how to figure out how to get the best exposure possible for any situation.
- Exposure is the amount of light captured on your sensor or film
- Not enough light = underexposed
- Too much light = overexposed
- Aperture is the hole in your lens that lets in different amounts of light
- A large hole is a small f-stop
- A small hole is a large f-stop
- A large hole creates shallow depth of field (sharp subject, blurry background)
- A shutter opens and closes to expose your sensor for different amounts of time
- A fast shutter speed freezes motion, but lets in less light
- A slow shutter speed lets in a lot of light, but can cause motion blur if subject is not still
- ISO is the amplification of the sensor
- HIGH ISO makes the image brighter, but creates noise
- LOW ISO makes the image darker, but gives you the cleanest result
Photos by Froggie
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This is an example of the tutorial style posts you can find on the newly launched Frogman’s Light School. Eventually, we will cover a variety of topics at every skill level, from beginner to advanced, so keep checking back.