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Understanding aperture in less than 5 minutes

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The yet to become famous Bucket Theory

Contrary to popular belief, it’s actually surprisingly easy to understand the various operations of a camera. To start with I’ll paint an uncomplicated picture of what is physically going on in relation to aperture.

Specifics

Lets break the camera down into its most simplistic functions. All cameras, from a box camera to the most outrageous professional SLR, are basically doing the same thing. They focus a specific amount of light onto a light sensitive material for a specific amount of time (the operative words being specific and amount). This is allowing you to make different choices about each photograph. You can then balance out the amount of light with the time the light is present to create an appropriate exposure.

The lens

The lens is a fancy tube with shaped bits of glass in it that focuses light; there is an adjustable hole through the centre that is called the aperture. In the camera, sitting between the lens and the light sensor or film, is the shutter. The shutter is a thin curtain. When you press the button it opens the shutter and lets light through to the sensor or film. The size of aperture (hole) in the lens lets a specific amount of light into the camera and glass in the lens focuses it on the sensor or film for as long as the shutter is open.

So lets explore the idea of an aperture. An aperture is another word for a hole or opening. I will draw a simple analogy with a garden tap. When fully open it lets a torrent of water through but it can be turned down to allow a few drops at a time flow through. In much the same way the aperture in our lens controls the flow of light.

The Bucket Theory

Drum roll please…….introducing the yet to become famous Bucket Theory! As an analogy, say you are filling a bucket with water. The first time you fill your bucket, only turn the tap on halfway; you have opened the aperture of the tap half way. With the tap only half open it takes quite a while for the bucket to fill with water. Now empty the bucket. This time, turn the tap on full; the opening or aperture in the tap is twice the size. The bucket fills in half the time OR we have doubled the flow of water through the tap. By having control over of the size of the opening in the tap we have control over two things; Time and Quantity. The time it takes to fill the bucket and/or the quantity of water flowing through the tap at any given moment.

Let’s substitute light for water and our lens for the tap. Now think about light coming into your camera. You need to provide enough light to make a correct exposure (fill the bucket). It’s like we are trying to fill the sensor or film with an adequate amount of light. By adjusting the opening in our tap we controlled how long it took to fill up the bucket. By adjusting the aperture in our lens we can make decisions about the amount of light that passes through to make a correct exposure.

So just like the tap analogy the aperture/hole in the lens controls two very important physical characteristics of working with light; Time and Quantity. How long it takes for adequate light to pass through the lens OR how much light can flow through the lens. or simply put a big aperture (big hole) more light flow; little aperture (small hole) less light flow. Big aperture less time (to fill up the bucket); little aperture more time (to fill up the bucket).

The aperture also controls depth of field, which will be more easily understood once you get your head around the way the aperture numbers work. I’ll get to that in a later blog.

So why are the aperture numbers on a camera SO FREAKIN STUPID!!!! They don’t make any sense. Big aperture little number, little aperture big number AAAAHHHRRRRGGG!!

Well the answer is so simple that once you see it, you will understand. Say we dial in the lens aperture at F2. It means that if you got a hole the size of the F2 aperture in the lens and turned it on it’s side it would fit 2 times between the sensor/chip in the camera body (film plane) and the middle of the lens. Big hole; little number.

If we set the aperture at F8, it means a hole the size of the F8 aperture, when turned on its side, would fit 8 times between the sensor/chip/film plane in the camera body and the middle of the lens. Big number; little hole.

So the F number is how many times any aperture be it 2.8, 4, 5.6 or 22 would fit between the lens opening and the sensor/chip/film plane. If you visualise that you are counting out how many of the holes would fit you will never be confused again. F22= 22 little apertures side on, F2=2 big apertures side on.

The sole aim of this blog is that you have a picture in your mind of what is physically happening in the lens. In future posts I will cover what that actually means as well as looking at shutter speed, ISO (digital chip/sensor sensitivity) and ASA (film speed) and depth of field. Once all of the elements are explained I will show you how they mesh together to drive the camera and give you the various options you have when taking a photo.

I would love for this to be the Famous Bucket Theory. If these ideas make sense to you then forward this blog to your friends. Teaching is a great way to learn so have a go at explaining this to someone.