Workshop Notes: Aperture


The participants of my workshops (The Basics) know that I believe that the knowledge of some basic technical aspects of photography will help you to improve your photography. In very basic terms a camera is a black box, which allows light in on the one side (through a lens) and records the image on the opposite side either on film or a digital sensor.

We need to control the amount of light for correctly exposed images. This works in two different ways. We can control the duration of the exposure via the shutter speed and the amount via the aperture.

Aperture at f stop 2.8

Let’s talk about aperture. So, what is aperture? Wikipedia describes aperture in this way: “In optics, an aperture is a hole or an opening through which light travels”. The nice thing about aperture in cameras is that we can control the size of the opening. By controlling the size, we decide on how much light goes through this opening.

When we set an aperture wide open (as in the image on the left), we allow the greatest amount of light to fall on the sensor. To control the size of the aperture, we change, what we call the f-stop (or focal ratio) via a dial on modern cameras. In order to this, you need to set your camera into Aperture Priorty (or Av) first. This sounds more complicated than it is. When we move the dial, we see rather strange numbers like 2.8, 4.0, 5.6, 8, .. We call these f-stops. Just remember, the smaller the number, the bigger the hole or opening of the aperture. If you are technically inclined, dive into the Wikipedia article about F-numbers. Wikipedia explains also the math behind it.

Most digital cameras that I have seen in my workshops move by 1/3 of a f-stop with each movement of the control dial. You need to do 3 clicks to change it by one full stop. Traditionally, on older lenses, the f-stop moves one full stop when you move the aperture ring. So, when I change the aperture from 2.8 to 4.0, I move it by on full stop.

Each full f-stop change ,doubles (or halves depending on which direction you go) the shutter speed to expose the image correctly.

Aperture at f stop 22
Aperture at f stop 22

Confused? Okay! Take your camera and try it.

If you normally shoot in Auto or Program mode, set your camera to aperture priority. The camera will automatically adjust for you the shutter speed when you change the aperture.

The aperture controls also the depth of field in your images. The depth of field describes the area in your pictures that you recognize as in focus and out of focus. When you open your aperture to its widest setting, you will see that the depth of field is shallow. In other words: Only a portion of your image is in focus. When you close the aperture (choose a bigger aperture number), you will see that a bigger area of the image is in focus.

You notice the effect mostly in cameras with bigger sensors (such as DSLRs). Point and shoot and phone cameras have tiny sensor that do not show this effect as intense as in cameras with bigger sensors (e.g. 4/3, interchangeable lens compact cameras and DSLRs).





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