Exposure basics

With a title like that, this article could really go anywhere, but seeing as this is a photography website i’ll take it to mean the basic settings (ISO, aperture and shutter speed) which combine to give us our desired exposure. These settings should be flexible for both compact cameras and also SLRs.

Of course, our lovely Gab will be going through this much more extensively in our classes over the coming weeks anyway, and while many of you may know some/all of this already i thought i’d put this together for beginners or as a refresher for more experienced people who may have forgotten a thing or two over the summer.

As i mentioned above, the three basic settings which combine to control the amount of light which reaches the sensor (or film) are ISO, aperture and shutter speed.

The aperture controls the size of the opening in the lens and hence, the amount of light which enters the camera. The aperture is measured in f-stops. For a wide aperture (lens mostly/fully open) the f-stop will be small, somewhere in the region of around f/4 or f/5.6 in most zoom lenses and maybe f/1.4 or f/1.8 for fixed lenses. When the f-stop is at the lowest possible value for the lens we say that the aperture is wide open and it is letting in as much light as possible.

Another effect of the aperture is the depth of field of an image, when you shoot with the aperture wide open it leaves a narrow range of what stays in focus with some detail in the background or foreground of the photo being left out of focus. This can be useful for isolating subjects. The picture on the left was shot with the lens wide open at f/1.8 and you can see that there is quite a narrow depth of field which has left the dog (isn’t Max lovely?) clear and in focus but the background quite out of focus.

The shutter speed is quite simply how long the shutter is left open during the exposure. The longer the shutter is left open, the more light can reach the sensor and this results in a brighter picture. However, unless you have a very steady hand or a tripod you will have to be careful not to set the shutter speed too slow or you can start to blur your image.

At ISO 6400 you can see that this image has become very grainy (especially in any dark areas of the photo)

The ISO is a more difficult concept to understand as changing its value doesn’t have as much of a physical affect on the camera. For film cameras, the ISO depends on what film you are using and what speed it is. The film is made up of many many tiny light-sensitive grains which record the image when the shutter is opened and they are exposed to light. A faster film speed will have bigger grains which mean that the film doesn’t take as long to fully record the image. The ISO is equally important for digital cameras even though there is no longer any film or grains to deal with. Instead, the light is recorded by photodiodes on the camera’s sensor and the ISO controls the sensor’s sensitivity to light. In a digital camera there will be a native ISO which the camera will preform best at. Any change from this native light sensitivity and the camera will compensate by trying to amplify the levels of light in the photo. This can be very useful in low light situations when you can’t afford to bring the shutter speed any lower without risking blurring the photo. There is, however, a trade-off in quality for higher levels of ISO. As the ISO increases, so does the noise/graininess of the photo.

Combining these 3 settings manually gives so much more versatility to your camera and allows you to shoot in situations which the auto settings on cameras might not be able to handle very well. One of the best ways to get the hang of using of them together is just to practice and experiment with different combinations until you are happy with your exposure.

Peter xoxo