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What is Aperture?

I’d like to deal with aperture first, as it’s at the front of the camera, and it seems a logical place to start.

Put very simply, aperture is a hole in the lens through which light passes. On all but the simplest and cheapest lenses, this aperture can be altered, from being as large as possible, to very small. The different apertures are assigned numbers, and just to get you off to a confusing start, the largest apertures have the smallest numbers, and the smallest apertures the biggest numbers. Thanks for that, Mr Inventor of Photography.

Larger Aperture <<<< >>>>Smaller Aperture

f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f64

The difference between each aperture is - wait for it - one stop. So from f2.8 to f4 is one stop, and from f11 to f16 is one stop, and so on up and down, back and forth. If you make the aperture one stop smaller, say from f5.6 to f8, you will let half as much light through the lens and into the camera. Not surprisingly, if you make the aperture one stop larger, say from f22 to f16, you will let twice as much light into the camera.

The correct exposure, followed by 2 stops more exposure, and 2 stops less.

Right, that’s the basics. Perhaps a little more detail will help you not only understand better, but also make you sound clever in front of your friends. Let’s talk about the numbers a little more. Why f8? Or f16? Knowing this will have no effect whatsoever on your photography, but since you asked, the number is a mathematical expression of the size of the aperture in relation to the focal length of the lense. Exciting, isn’t it! What is useful to know though, is that f8 on one lens, should give you exactly the same exposure as f8 on another lens, and the same is true of any aperture. This means if you’ve got the perfect exposure for a shot, but decide you want to shoot it with a different lens, you don’t need to start all over again, just use the same aperture on the new lens. Clever that.

Actually, one other thing. Don’t panic when you examine the progression of numbers and notice that they don’t actually follow a perfect mathematical sequence. You do not need to know why this is, I’ve lasted my whole photographic career without a satisfactory explanation, so I think we can get through this beginner’s guide without one!