Understanding Aperture, ISO and Shutter speed

From taking test photographs this week and from the ideas given to us by Steve in the lesson and also what I have read about on the internet this is what I understand about the following.

Aperture

This is basically the size of the hole in the lens used for taking a photograph, it is measured in "f numbers" and just to confuse matters the smaller the "f number" the larger the aperture. This means an aperture f22 is a smaller aperture (or hole) than f5.

The larger the aperture in the lens means the light will get in the lens quicker than a smaller aperture. This means in theory that if you are using a fast shutter speed you will need a larger aperture to let as much light in as possible so the photograph is not under exposed.

Another area that aperture will change is the depth of field of a photograph, this means how much of the photograph is in sharp focus. A large aperture such as f2.8 will mean a shallow depth of field meaning only a small area of the photo will be in focus and the foreground and background will be out of focus. However if you use a smaller aperture say f22 then most of the photograph will be in focus from foreground to background.

Shutter Speed

This is how fast the shutter opens and closes to take a picture. the shutter speeds range from (on my canon 500d) 1/4000th of a second to 30 seconds. I can take this higher than 30 seconds to "bulb" setting which means that the shutter will sty open for the length of time I keep the shutter button pressed down (my remote shutter release has a lock setting so can leave it open as long as I need to.

For shots showing movement such as water moving in a waterfall using a slower shutter speed will make the water look as if it is moving, however a faster shutter speed will make the water look like it is frozen in time. When using slower shutter speeds you will need to use something to help steady the camera such as a tripod otherwise you will get camera shake/blur. Shutter speed is related to aperture and need to be adjusted accordingly as using a fast shutter speed with a small aperture will lead to under exposed shots as the shutter speed is not allowing enough light into the camera to take the photograph.

ISO

ISO is basically how sensitive the sensor is, the smaller the number say 100 is less sensitive than 400. The good thing of DSLR over 35mm SLR is the fact you can change the ISO for each shot. Whereas when using film and you loaded a 400ISO film you were stuck with that until you had used all the film. The issue with ISO is the larger the ISO number the more light noise you will get on the photograph. Ideally you need to set the ISO as low as you can for each set of photographs. This means on a bright sunny day you could use an ISO of 100 or 200 however for a dull overcast day you may need an ISO setting of 400 or 800. My canon 500d has ISO settings from 100 upto 3200.

There are times that when taking photos in low light that you may need to use a low ISO and I will try to show these later.

Here are a few links for areas on the internet explaining ISO, Aperture and Shutter Speed (click on the links below)

ISO

Aperture, depth of field & shutter speed

In my next few blogs I will show examples of these areas.