Meeting Tonight

The 3rd meeting is this evening and I am looking forward to it. Fingers crossed more of the members will be able to attend. 


I had promised to explain certain things about manual settings on SRLS.


Aperture

What does 'aperture' mean?

The term 'aperture' refers to the opening in the lens that lets light into the camera. Adjusting the aperture value changes the size (diameter) of the aperture, which will affect the amount of light that reaches the imaging sensor in the camera (the digital camera equivalent of film). Obviously, if you set a wide aperture a lot of light will be allowed to reach the sensor, whilst setting a small aperture reduces the amount of light that reaches the sensor.

You can change the aperture value in the following advanced modes:

1. Av (Aperture-priority AE) Mode - aperture can be changed and the camera will attempt to set the appropriate shutter speed to correctly expose the photo
2. P (Program AE) - turning the dial changes the shutter speed and aperture setting combination (as part of a program)
3. M (Manual Exposure) - where both shutter speed and aperture values can be set as desired

Measuring Aperture Size

Aperture size is represented using f-stops. A large f-stop represents a small aperture - the lens will have a small opening and not let much light through to the imaging sensor. A small f-stop represents a wide aperture - the lens will have a large opening and therefore let a lot of light through to the imaging sensor.

This is the case because f-stops represent the ratio between the diameter of the aperture and the focal length of the lens. As an example:

• if the aperture value is shown as f/4 this means that the aperture's diameter is 1/4 (25%) of the focal length of the lens
• if the aperture value is f/32, the aperture's diameter will be 1/32th of the focal length of the lens - a much smallerdiameter than the 1/4 size.
  
  
  Clearly if you set a wide aperture a lot of light will be allowed to reach the sensor, which in turn means that the camera can use a faster shutter speed in order to obtain the correct exposure. This is because the sensor only needs to be exposed for a shorter period of time before it will have received enough light to expose the photograph.
  Conversely, setting a smaller aperture reduces the amount of light reaching the sensor and means that a slower shutter speed must be used if the camera is to properly expose the picture - more time is needed to ensure enough light reaches the sensor.
  Therefore if you are in a dark environment and want to take a properly exposed photograph without using a flash and with the shortest possible shutter speed (to minimise/avoid camera shake) you should:
  1. Set the widest possible aperture (bearing in mind the affect on depth of field discussed below) and
  2. Select a higher ISO speed (bearing in mind the potential affect on quality discussed in the previous article).
  • I will blog soon about shutter speeds and ISO's, promise :)
  
  
  D