Photography Basics: Controlling Exposure
We have covered this topic several times and it still is one of the most common emails we get so we are reposting this older article to help new people be able to find it easier.
In this post we are going to look at how to control exposure by manipulating the different settings on the camera such as ISO, Shutter, and Aperture.
What is exposure?
Exposure is, simply put, the amount of light that enters the camera and hits the sensor. The more light that hits the sensor the brighter the scene will be. If too much light hits the sensor, parts of the image will be “blown out”, this is considered to be over-exposed. A scene that is too dark and the details in the shadows are lost is under-exposed.
Under Exposed Image
Over Exposed Image
How to control exposure
There are three camera settings that control the exposure, these are:
- ISO speed
- Controls the sensitivity of the sensor to light
- Aperture
- The aperture controls the size of the diaphragm over the shutter, the smaller the aperture number the more open the diaphragm is, allowing more light to enter.
- Shutter speed
- The slower the shutter, the more light will enter the camera
We will look at these settings in more detail to see exactly how the play together later. First, you need to start thinking of light in terms of “stops”. A stop is not an exact amount of light, it is a relative amount of light, each stop of light doubles the amount of light. For example, if we have a single lightbulb as our base light source, adding a second lightbulb (doubling the amount of light) increases the light by one stop. If want to increase the light by another stop we have to again double the amount of light to four lightbulbs. Understanding this is going to be the key to understanding how the different camera settings affect our exposure.
ISO Speed
As already mentioned, the ISO speed will control the sensitivity of the sensor. The lower the number, the less sensitive. For low light you will need a higher ISO number to make the sensor more sensitive. The downside is that the higher ISO the more digital noise (grainy look) will show up which will degrade the image quality.
Each time you double the ISO speed you increase the exposure by one stop, so ISO 400 will give you one stop of exposure more than ISO 200, and ISO 800 will give you one more stop over ISO 400 etc. Some cameras have some in-between ISO settings to provide a finer level of control.
You currently see high ISO performance as being a major selling point for new DSLR cameras as this allows them to shoot in lower light conditions with less noise.
Pro: Higher ISO allows shooting in lower light conditions
Con: Higher ISO settings result in more digital noise
High ISO Digital Noise
Aperture
Aperture is a little confusing because the larger the number the smaller the size. The largest aperture lenses are f/1.0 although most of the good prime lenses start at f/1.4 – f/1.6. Zoom lenses typically are not available that can do more than f/2.8.
So besides letting in more or less light, what does the aperture actually do? The more light that comes in at a particular shutter speed, the shallower the depth of field. If you want more depth of field you use a smaller (higher number) aperture setting.
Pro: Larger apertures allow more light in and thus allow shooting in lower light conditions
Con: Larger apertures reduce the depth of field which may not be desirable
Shallow Depth of Field
Deep Depth of Field
Shutter
The faster the shutter, the less light enters the camera, the slower the shutter the more light will enter the camera. If you are shooting in low light conditions, you may need a slower shutter speed, however, too slow of a shutter and you can introduce blur from the subject moving, accidental camera movement, or both.
Sometimes a little blur can help portray movement and action, a sharp bike rider with a blurred background will make the rider look like he/she is moving fast where a tack sharp image shows no motion at all and would make the same image look boring. While blurring on other images can ruin the image.
Pro: The right shutter speed can really make an image more dramatic. Fast shutter speeds can freeze action, slow shutter speeds can add a dramatic motion blur.
Con: Fast shutter speeds require lots of light, slow shutter speeds are harder to control
 Fast Shutter Speed |
 Slow Shutter Speed |
Summary
By understanding the three variables that control exposure along with the pros and cons of each one, you will be able to better control the different options that are available to you.
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I really like the fact that you are puting this series together. The part that I find is always missing from these discussions is how to put everything together. How do you manage to get you mind to connect what they eye sees to a technique that fulfills that vision? Are there exercises that you find work to develop this sense or is it just persistent trial and error?
I mentioned this is a podcast a couple of weeks ago. Most people will struggle at this for a while and one day it all just comes together. The more you shoot, the faster it will come. I think it was right around my 10,000th image and all of a sudden everything started coming together. Maybe I could have been faster if I had more people to talk to and discuss it with, or more tutorials to read (which is my goal, help people get there faster). I suggest shooting in Aperture Priority the most, ISO is simple (the higher number the darker you can shoot in but it adds noise) and shutter is simple (the slower the shutter the darker you can shoot in but it can add blur) but aperture is harder. The larger the aperture the smaller the number, plus it dramatically affects the image's depth of field which can make or break an image. Hope this helps.
I really like the fact that you are puting this series together. The part that I find is always missing from these discussions is how to put everything together. How do you manage to get you mind to connect what they eye sees to a technique that fulfills that vision? Are there exercises that you find work to develop this sense or is it just persistent trial and error?
I mentioned this is a podcast a couple of weeks ago. Most people will struggle at this for a while and one day it all just comes together. The more you shoot, the faster it will come. I think it was right around my 10,000th image and all of a sudden everything started coming together. Maybe I could have been faster if I had more people to talk to and discuss it with, or more tutorials to read (which is my goal, help people get there faster). I suggest shooting in Aperture Priority the most, ISO is simple (the higher number the darker you can shoot in but it adds noise) and shutter is simple (the slower the shutter the darker you can shoot in but it can add blur) but aperture is harder. The larger the aperture the smaller the number, plus it dramatically affects the image's depth of field which can make or break an image. Hope this helps.
I really like the fact that you are puting this series together. The part that I find is always missing from these discussions is how to put everything together. How do you manage to get you mind to connect what they eye sees to a technique that fulfills that vision? Are there exercises that you find work to develop this sense or is it just persistent trial and error?
I mentioned this is a podcast a couple of weeks ago. Most people will struggle at this for a while and one day it all just comes together. The more you shoot, the faster it will come. I think it was right around my 10,000th image and all of a sudden everything started coming together. Maybe I could have been faster if I had more people to talk to and discuss it with, or more tutorials to read (which is my goal, help people get there faster). I suggest shooting in Aperture Priority the most, ISO is simple (the higher number the darker you can shoot in but it adds noise) and shutter is simple (the slower the shutter the darker you can shoot in but it can add blur) but aperture is harder. The larger the aperture the smaller the number, plus it dramatically affects the image's depth of field which can make or break an image. Hope this helps.