apertures

The other half of the exposure, (that moment when we press the shutter release), is the APERTURE.
Think of it as the twin brother of the shutter speed.

Under any particular lighting condition, combining a SHUTTER SPEED with the right APERTURE setting will give the correct EXPOSURE.

Don't panic, it's not rocket science. Essentially we have a hole in the middle of the lens, (the aperture), and a length of time that hole is open for, (the shutter speed). Open the hole for the right time and you'll have a perfect exposure.

Now, modern camera's will actually do all this for us. However, the vaguely interesting thing about apertures is that they have an effect on how focused our finished image will be.

Apertures are expressed as f-stops.
A large aperture (big hole) is a small number; f2.8
The corresponding shutter speed for this aperture, under average lighting conditions would be relatively fast, because it's a big hole, it lets the right amount of light in quickly.

Large apertures mean faster shutter speeds, but the area of our image that will be in focus is limited.


A small aperture (small hole) is a big number; f22
The shutter speed for this aperture, under the same lighting conditions, would be relatively longer. It's a small hole, so it takes longer for the right amount of light to pass through the lens.

Small apertures need longer shutter speeds, but a greater proportion of our image will be in focus.


The top image was made using a large aperture, the lack of focus created by this large aperture is used to deliberately isolate the first post of the railings.

The bottom image was made using a relatively small aperture, keeping most of the image in focus from front to back. This has had the effect of making the leading lines of the composition more effective.