Between The Sprockets A photography blog

What’s it all mean?

Photography can be as simple as you want it to be.  With modern film and digital cameras, you may never know exactly how it works and still be able to produce some amazing images.  A little bit of knowledge can be amazingly powerful though, and with that in mind, I'd like to try and explain some concepts that will help you understand your camera a little better, and help you bring your photos to life.

Shutter Speed

Shutter speed is probably the easiest concept to handle.  Shutter speed is how long the film or digital sensor in your camera is exposed to light for.  Traditionally this is measured in fractions of a second, for example a shutter speed of one sixtieth of a second would be written as 1/60 (1 second divided by 60).  This will normally be shortened to just "60" on most cameras and light meters.  The higher the number, the less light gets through to the film / sensor.

Normally you will have the following shutter speeds available to you:

1, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000, 2000

There may be more or less, depending on the age of your camera.  The jump between any two consecutive speeds here (eg. 60 to 125, or 4 to 8) is called a stop.  Some modern cameras can use shutter speeds that fall between these numbers, or half stops.  Each shutter speed lets in half as much light as the preceding one, for example, 8 lets in twice as much light as 15.

Aperture

Aperture is essentially a measurement of the size of the opening of the lens in relation to the film.  The wider the opening, the more light hits the film.  Aperture is normally measured as f-stops, and you will see the maximum aperture your lens can do printed on the front of it (normally), eg. f2.8 (commonly printed as 1:2.8 on lenses)

The actual aperture numbers are calculated as a ratio of lens diameter and distance from the film.  The exact formula isn't important, but what is important is remembering that a smaller number means a bigger opening.  Typically aperture numbers will look like this:

f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, etc.

Once again, the jump between two of these numbers is a stop, and let in half as much light as the preceding number.  Using this knowledge, you can see it's possibly to adjust your shutter speed one stop (say, from 60 to 125) as long as you also adjust your aperture as well (say from f8 to f4).  The same amount of light will hit the film / sensor.

Aperture can also have irregular numbers, such as f3.5.

A lot of zoom lenses have two different minimum apertures.  The widest aperture (smallest number) is the maximum aperture at the widest angle, and the larger number is the maximum aperture at the longest zoom.

Depth of Field

Depth of field is a term used to describe the amount of your photo that is in focus.  A large depth of field means more of you photo is in focus, and a small depth of field means less is in focus.

Depth of field is directly related to the aperture value you are using.  A big aperture (remember, big aperture means small number) of f2.8 for example will mean that a small portion of your photo will be in focus.  A small aperture (large number) of f16 for example will mean a lot of your photo will be in focus.

How much will be in focus depends on the length (in mm) of your lens, and how far away you focus the camera.  I won't discuss these calculations, as I believe it's easier to try them out on your camera to see for yourself.  Below is some examples of what different apertures do to your photo.

Some cameras have a depth of field preview button.  By default, most cameras display the image in the viewfinder at the widest aperture available on the attached lens.  This is done so you have a bright, clear view of what you are framing.  When you press the depth of field preview button, the camera closes the aperture down to the selected value.  The picture in the viewfinder may get very dim at this point, don't worry though, you photo will still be exposed correctly, it's just that the smaller hole (the high f-stop) lets in less light (which is compensated for by a slower shutter speed).  This will show you exactly how the focus will look on the final image (but not the exposure).

This information can seem a little daunting, but once you get the hang of how the numbers all relate to each other, it becomes easier to get the photo you want, not the photo the camera thinks you want.  Don't worry about remember the numbers exactly, they will be available to you on your lens / camera somewhere normally, it's the understanding of the relationship between aperture and shutter speed and their effect on depth of field that will help you start to take better photos.