5. Aperture

Pictures by Bill Moore

The other major element that affects how much light gets into your camera to take a photo is the aperture. The aperture is the size of the hole that light pases through to reach the film or sensor in the the camera. This may sound unimportant but it can have a big impact on how your pictures come out.

First F-Numbers or F-Stops. These measure the size of the aperture. In simple terms the lower the F-Stop (e.g. F2.8) the bigger the aperture. High numbers indicate a very small aperture (e.g. F18).

The F-stop also influences what is known as the ‘depth-of-field’. This refers to the distance between the nearest and farthest objects that would appear in focus. A shallow depth of field will keep the subject in focus but anything closer and farther away will be out of focus. This makes focussing correctly absolutely vital. A deep depth of field will leave most things in focus from close object to objects a long way from the camera.

Low F-Stop:

  • In low light a low F-stop will make the aperture larger and allow more light into the camera and compensate for the lack of light in the surroundings to take the picture.
  • Focussing on the subject is really important though. The depth of field will be very narrow so changing the focus of the image will have a big impact on what is and isn’t in focus.
  • This can be good for portraits or pictures of objects or flowers where you want the subject of the photo sharp and in focus but the background blurred.

High F-Stop:

  • The higher the number, the smaller the aperture and the less light that will be able to go into the camera to take the photo. This will mean a slower shutter speed is necessary.
  • However, the depth of field will be very deep meaning that much of the photo will be in focus.
  • This is often good for landscapes where you want to keep as much of the scene in focus as possible.

Examples by Bill:

001 Flower f22
f22

Flower at f22: The large depth of field given by the f22 aperture (a high f-stop) renders the background too sharp and we can see too much of the detail behind the flower. This is distracting us from the flower which is perfectly in focus.

002 Flower f1.8
F1.8

Flower at f1.8:  The very shallow depth of field throws the background out of focus which is much less distracting. However,       the rear petals of the flower and the tips of the closest ones are not sharp. The depth of field can not be more than a few centimeters and we can not get the entire flower in focus.

003 Flower f4.0
F4.0

Flower at f4.0: Here the background remains out of focus but allows most of the petals to be in sharp focus. A good compromise isolating the flower, the focus of our attention, but keeping it sharp.

004 Landscape f1.8 distant focus
F1.8 Distant Focus

Landscape f1.8 Distant Focus: At f1.8 Bill can not get the whole scene in focus. In this case the bushes in the foreground are out of focus which looks strange. This is not always desirable in a landscape.

005 Landscape f1.8 near focus
f1.8 Near Focus

Landscape f1.8 Near Focus: Still at f1.8 our depth of field remains too narrow. By focusing on the bushes in the foreground the wider landscape is now out of focus.

006 Landscape f22 all in focus c
f22 All in Focus

Landscape f22: By closing down the aperture to f22 both the foreground and the distant landscape have come into focus and a more pleasing landscape is created.

Bear in mind that when taking the photo of the flower at f1.8 we had just a couple of centimeters depth of field but in this landscape at f22 we have perhaps 2 or 3 miles in scenery in focus!

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