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Friday, November 15, 2013

Introduction to Photo Exposure Terms - Part 1 - Shutter Speed

I recently presented at the Australian Art Show in Melbourne and Sydney, on a number of aspects of photography. The ‘Introduction to Photography Exposure Terms’ for beginners was popular, so I’ve turned it into a four part blog – Part 1: Shutter Speed, Part 2: Aperture, Part 3: ISO and Part 4: Exposure.

When you are a photography beginner, information is a great way to understand the basics and to help build some confidence. Of course, the best way to learn is to just get out there and get shooting!
What is a ‘stop’ of light?
A stop of light is either half or double the existing exposure.  So, when you add light (using the ‘+’ on the dial) you are making your photo brighter and when you reduce the light (using the ‘–‘ on the dial) you are making your photo darker.
If you under expose the image by one stop you are halving the amount of light that is hitting your sensor.  If you are over exposing by one stop then you are doubling the amount of light that is hitting your sensor. 
A number of cameras have a dial that has a +1, +2 and +3 with a corresponding -1, -2 and -3 on the same dial.  This is called the exposure compensation dial and allows the photographer to instantly over or under expose the photo. 
Command Dial
All DSLR cameras have a way of changing the three main exposure settings (shutter speed, aperture, ISO). The most common way is through a command dial which is found on one of the shoulders of the camera.  The photo here is from a standard command dial on a Canon camera. The letters stand for:

·      M – Full Manual control over shutter speed and aperture
·      AV – Control over the Aperture Value, in this mode the camera will automatically set the appropriate shutter speed to give the correct metered exposure based on whatever aperture you select
·      TV – This gives manual control over the Time Value (shutter speed) and the camera will again automatically select the correct aperture value depending on what shutter speed you select
·      P – This is the Program mode which automatically selects an aperture and shutter speed combination to give the correct exposure, but allows you to override this combination if you wish
 
Shutter Speed
Shutter speed refers to the length of time your shutter exposes the sensor of your digital camera.  The longer the shutter speed is, the longer your sensor is exposed.  Changing your shutter speed will do a couple of things:
·      Lengthening the shutter speed will let in more light
·      Shortening the shutter speed will let in less light
·      The slower the shutter speed, the more likely that any movement from the subject or the camera will show up in the image (and sometimes you may want this…)
·      If you have an extremely short shutter speed you can freeze movement
Shutter speed is generally written as ‘1/125’ (which means 125th of a second) but on a camera dial it will usually be shown as ‘125’.

Examples

The photo above was shot at 1/8000th of a second using high speed flash. It shows how a quick exposure can freeze movement and allow you to see details that you would otherwise miss. The shutter was too fast for any background detail to appear.
 

This photo is shot with the exact same set up but at a shutter speed of 1/20th of a second.  The results show the subject is blurred and has lost all fine detail and the photo no longer looks focused.  The background has detail because the shutter speed has stayed open long enough for the grass to appear. 

Next week, Part 2 of our ‘Introduction to Photography Exposure Terms’ will be on aperture.

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