The Exposure Triangle
Taking your camera out of Auto…
The components of “Exposure” are a combination of the ISO, Aperture, and Shutter Speed.
The relationship between these three factors of exposure is a balance of light. When you snap the shutter on the camera, you are capturing Light.
Before you read on, I’d like to say you don’t have to shoot in Manual mode all the time. Shutter or Aperture priority modes are very useful and will produce excellent results if your camera is set accordingly. These exposure controls must always be taken into consideration if shooting anything other than Auto settings.
Steps I take when shooting
- Determine the ASA/ISO
- Which is most important? Motion or Depth of Field (Shutter Speed/Aperture)
- Set the Aperture and Shutter Speed according to my needs
- Check for warnings. (camera shake, over/under exposure, use the Histogram)
- Review the shot and re-shoot if needed.
- ISO/ASA…How quickly light is absorbed.
The ISO or ASA as it was referred to in traditional film photography is the measurement of the Sensitivity to Light of the film. ASA 32, 64, 100, 200, etc… In digital cameras this is the same rating system only it refers to the sensitivity of the Digital Sensor in the camera. The lower the number, the less sensitive to light, and the finer the grain in the photo. For example, an ISO of 64 will give a much cleaner and crisper image than an ISO of 800. The tradeoff would be Noise or the visible grain in the image with a higher ISO.
- Aperture…The amount of light allowed to flow through the lens.
The Aperture is the opening of the iris in the lens of the camera. Just like the pupil of your eye. The larger the opening the more light it will allow through the lens to the digital sensor. These openings are defined by f/stops. The smaller the number the larger the opening. An f/2 is a large aperture, where as an f/22 is a very small aperture. The relationship between a large or small aperture is the Depth of Field. The larger the aperture the smaller, or shorter the depth of field will be.
The shot on the left shows a depth of field equal to about 3 feet or 1 meter. If this shot was captured at an f/16 the tree in the upper right-hand corner would also be in focus.
(Click on the photo for a larger view)
Up till now I’ve been saying the aperture is the deciding factor of the Depth of Field, and it does play a major role. The lens length also has an effect. The longer the lens the shorter the Depth of Field and a Macro lens will always have a shallow Depth of Field. So it can be said the higher the magnification the shorter the depth of field. The photo above has a very narrow depth of field due to the type of lens more so than the aperture.
The Shutter Speed is measured in 1/1000’s of a second. So if you are shooting at a shutter speed of 250, this equals 1/250 of a second. In other words, it will allow light onto the sensor for a period of 1/250 of a second. The effect of the shutter speed on your image is the freezing or blurring of any movement within your frame. This includes camera shake. An extended shutter opening, 1/30 – 8 seconds for example, will allow for the capture of an image under low to extremely low light conditions. A tripod would be necessary in this case.
In the photo of Jake Hayes above, he is coming out of this hair pin corner at about 45 mph (65 kph) there are a couple of things in my favor. One is the position of the bike in relationship to the camera. If the bike was broadside of me at that speed, there is a very good chance the shutter speed would have been too slow to freeze the action without panning the subject. The second thing in my favor was the available light. I could easily use both the 100 ISO and the 1/500 shutter speed. If you look at the front tire of the motorcycle you can see the blur caused by the rotation and yet the rider’s face is clear.
This is a great example of a panned shot, use of a long lens and a slow shutter speed to show the speed involved. The blur of the motorcycle in the background is amplified by the panning of this shot in the opposite direction. The subject in this case is broadside to the camera. If this was shot with a faster shutter speed there is a good possibility the motorcycle in the foreground and the rider’s face would have come out crisper and cleaner than it is. These trade offs are learned through shooting and re-shooting more so than simply reading and educating.
These bamboo tree shots were taken on a windy day. You can clearly see the difference. Same camera, lens, ISO and both taken on manual. Click on either photo for a larger view.
Now looking at these three controls of exposure, you should also see how they affect the overall outcome of the image. The amount of available light is the first defining factor as to how you set your controls. The second factor is the objective of you shot. By that I mean do you want your image to be grainy or crystal clear (ISO), what depth of field do you need (f/stop) and thirdly do you want to show movement by introducing blurring of your subject or freeze the subject movement (Shutter Speed). And don’t forget to look at the Histogram for proper tone and contrast. Again something I’ll stress is the need to experiment and take multiple shots until you’re comfortable using you camera on “anything other than AUTO”…