What *is* 'Aperture' anyway?

One of the first questions people ask when they get a camera with any sort of manual controls is "What is Aperture?".

Like many things, there's a simple, literal answer, or there's a more complex but useful answer. I'll try to cover both here.

 The simple, literal answer is that Aperture is the size of the hole in the lens through which the light travels on the way to the sensor (or film - if I say 'sensor', the same applies typically on a film based camera). A bigger aperture will let through more light than a smaller aperture.

Think about water flowing through a pipe - if it's a very thin pipe (small aperture), you can't get as much water (light) through the pipe. Aperture therefore plays a critical part in determining how much light hits your sensor, and since photography is all about capturing light, it's important.

More after the break...

Exposure, indecent or otherwise

When we take a photograph, what we're doing is exposing a light sensitive medium (film or digital sensor) to light, and recording the light as it falls on that medium.

That's it. 

That's *all* photography is.

What? You want more?

OK - so that is all that photography is. But understanding how that works, what influences it, and how to control it is the difference between a good technical photographer and a bad one.

Note that I didn't say a good photographer. I said a good technical photographer. Understanding the technical elements will only get you so far - to be a good photographer requires an understanding of composition, of artistic vision, of your subject(s)... this blog focuses on the technical elements.

More after the break...

There are three things that influence the amount of light recorded on your sensor/film:
1 - how long do you expose the sensor to light
2 - how much light can pass through the lens and onto the sensor
3 - how sensitive the sensor is to light

Imagine that your sensor is a bucket, and you have to fill it up using a hose pipe.
1 - how long do you turn your tap on?
2 - how wide is the hose?
3 - how big is your bucket?

If your bucket is big, and needs a lot of water, you could use a small hose and let it run for a long time, or you could use a huge hose and only let it run for a short time.

It's the same with light. If your sensor is not very sensitive to light, then you need to expose it to light for longer, or you need to gather more light for the duration you're exposing the sensor to light...

The three things above that control exposure relate exactly to the three major settings on a camera:

1. Shutter speed - this controls how long the sensor is exposed to light

2. Aperture - this controls the size of the opening in the lens that lets light onto the sensor

3. ISO - this controls how much light is needed to capture the image on the sensor