Lesson number 3: Aperture

I’ve had a couple more photos accepted on dreamstime and this is always a cause for celebration, so following on from my previous blog posts on camera basics, here is my celebratory beginners guide to apertures.

When trying to get to grips with apertures, I thought of the camera as being similar to my eye. Both have a lens and in both cases the lens has an ‘aperture’. In my eye the aperture (i.e. the size of the hole) is formed by the pupil, the size of which is controlled by my iris. The pupil is effectively a hole punched through the iris to let the light in. Contractions or relaxation of the iris shrinks or widens the hole. In a camera lens (at least most camera lenses), the aperture is formed by a diaphragm consisting of a number of overlapping blades. The diaphragm loosens or tightens to vary the size of the resulting hole.

The most obvious effect of varying the aperture size is to vary the amount of light which enters the camera and hits the sensor (more on why this is useful later). Thinking of my eye again, if I stare at my car headlight, my pupil contracts, so that less light burns the back of my eye ball. In the dark it dilates, so that more light can enter and I can see where I am going without walking into things.

In the photography world aperture is measured in f-numbers. Confusingly, as f numbers go up, the size of the aperture decreases (this is because it is actually a fraction, i.e. 1/f. So 1/4 is actually smaller in value than 1/2).

So an aperture of 22 (1/22) describes a smaller than one of 5.6 (1/5.6). On most lenses, the aperture size is varied in discrete steps called f-stops or stops (for example a lens may have this range of available aperture sizes: 3.5, 4.0, 4.5, 5.0, 5.6, 6.3, 7.1, 8.0, 9.0, 10, 11, 13, 14, 16, 18, 20, 22, 25, 29, 32, 36).

We now know that those numbers listed are going from a large aperture to a small aperture. But where do these seemingly random values come from? The maths behind this is, as usual, complex. Put simply, as you go from one f-stop down to the next (say 22 to 20), you are increasing the size of the aperture so as to double the amount of light entering the camera.

This brings me onto the second source of confusion, something which caused me huge frustration when I first bought my camera. I noticed that on my lens was written f3.5 - 5.6, and I spent many hours scratching my chin trying to work out what this might mean. It made me very cross, until eventually I read my manual. These values are the write your text hereat the write your text here. This means that when my lens is set to 18mm, the maximum aperture I can set it to is 3.5. When set to 55mm, the maximum aperture is 5.

So that’s the basics covered. My coffee break is over. Next I will post about shutter speed, and how this combined with the aperture setting will give you control over your photography and allow you to take photos like this:

Again, all this stuff is basic but it is stuff that confused me in the past so if it helps anyone, then great!

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August 23, 2012


thanks for sharing :)

August 18, 2012


great blog. thanks for sharing :)

August 16, 2012


Excellent. I look forward to more.

August 16, 2012


Excellent. I look forward to more.

August 16, 2012


Another good post. Keep them coming.

August 16, 2012


Thanks for the correction! Good point.

August 16, 2012


Nice blog, but you made a mistake! You listed 1/3 stops, so if you go from 22 to 16 you double the amount of light that enters your camera.

August 14, 2012


Nice blog!

August 14, 2012


Thanks for sharing, veri useful!!!

August 13, 2012


GReat info, thanks for sharing.

August 13, 2012


Thanks for sharing the info.

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Photo credits: Kim Deadman.