Image Exposure Fundamentals
Have you ever taken a photo that was way too dark or light? In most cases, this is due to the camera automatically selecting the incorrect settings to correctly capture what the eye is seeing. Because of this, it is nice to have camera that you can manually set each of the three exposure settings. A cameras’ automatic exposure system will attempt to create an image that has an overall value half way between black and white; this is not always ideal. For example:
The main three settings that control an images exposure are:
Every lens has an aperture range, also called the f-stop. This aperture range allows you to control the amount of the scene that is in focus. A higher f-stop number means more of your scene is in focus. A lower f-stop means a smaller area of the scene is in focus, rendering a stylish look. If your f-stop is set at f/32, for example, the majority of your scene will be in focus. However, if your lens has the ability to go down to f/2.8, only a small portion of your scene will be in focus while the rest is blurred for that softer, more stylish effect.
Think of your shutter speed as the gateway that allows more or less light into the camera, depending on your needs. The longer the shutter is open, the more light is allowed to enter the camera to create the picture. Fast or slow, it's easy to adjust to the perfect shutter speed for any lighting situation with a DSLR. In low-light settings, it makes sense to have a longer shutter speed to let in more light. It's just the opposite in bright situations.
Why does it matter to me? When it comes to your kid's soccer game, it won't matter whether you capture the big goal if the picture ends up looking like a blurry mess. A faster shutter speed will freeze the action, making unwanted blur a thing of the past. On the other hand, you might want a degree of motion blur for style or artistic value. A slow shutter speed will allow the subject to move during the shot, creating motion blur.
ISO sensitivity is a measure of how sensitive your sensor is to in-coming light. In low-light situations, your sensor needs to be more sensitive to the available light in order to create a recognizable image. In bright environments, the sensor should be less sensitive.
Here's a simple way think of it:
Darker environments call for higher ISO, while brighter scenes require a lower ISO number.
Some cameras have an ISO range that goes up to 6400 or higher. Keep in mind that the trade-off with higher ISOs is more grain, or "noise" in the image.
A good rule of thumb is to always use the lowest ISO you can get away with. That way you have proper exposure with as little graininess as possible. The great thing about a DSLR is that you can choose manual control of your ISO sensitivity. But as always, if you're a beginner, just set your ISO to auto and let the technology do the work for you.
If it sounds like aperture, shutter speed, and ISO are all connected, you're right. When you use them together, you have your "exposure." Here's a good analogy to help make sense of these settings: Think of getting a glass of water from your kitchen faucet. You can break it down into three steps:
1. Turn on the faucet
2. Leave the faucet on long enough to fill the glass
3. Drink as much of the water as you need
Exposure is similar. But instead of water, we're talking about light. There are still three
1. The aperture is the faucet that that lets light in
2. Your shutter speed is a measure of how long the faucet is turned on
3. ISO is a measure of how much light is needed to expose the image
Choose what is Important to You
By setting the three image exposure settings appropriately, you will get vastly superior image results. If what’s important to you is what is in focus, setting the correct Aperture should take priority. If you are trying to capture fast moving subjects, you should concentrate on the Shutter Speed, and if you are shooting in low-light, you should increase the sensitivity of your camera by boosting what ISO the camera is set to.