Introduction to Exposure - Page 1

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  • Exposure in photography is the capture of light.
  • What parts of the camera allow us to control the exposure?

* All elements of exposure work together. *

  • The Lens
  • ............. (1) Collects light.
  • ..............(2) Controls the amount of light we collect via the Aperture
  • ..............(3) Focuses the scene onto the sensor
  • ..............(4) Determines the angle of view. ( Focal Length ) ie: how much we can see.
  • .
  • .... The Lens Aperture
  • ............... The "hole" through which light from the scene is gathered. Usually the aperture can be varied.
  • ................ The size of the aperture is measured in F-stops (F).
  • ................ The F-stop is the ratio between the focal length and the size of the aperture.
  • ........................ eg: A 50mm focal length lens with an aperture of 25mm would have a F-stop of 1:2 or F2.
  • ........................ Therefore F2 is a larger aperture than F22 ( The F number is a ratio)
  • .................. "Fast" lenses have larger apertures. IE: An F2 lens is faster than an F5.6 lens.
  • The main thing to remember is: The larger the F stop (smaller number) the more light is let througfh the lens
  • .
  • The lens aperture also controls how sharp the image will be.
  • ................... ie. Are objects at different distances from the camera all sharp or is just one of the object sharp.
  • ................... This is called depth of field (DOF)
  • .................... A picture taken at F16 will have a lot more depth of field than one taken at F2.
  • .
  • There is a lot more to lenses than the above and may be covered in a future tutorial.
  • .
  • Here are two photographs taken at (1) Large aperture and (2) smaller aperture.
  • Notice the zone of sharpness in each.
  • One of the main reasons for controlling aperture, beside to get the correct exposure, is to make creative use of depth of field (DOF)
  • Depth of field (DOF) is almost a complete topic itself and may be covered in another tutorial (to be written)
  • Larger pictures, in a new window are available by clicking on each picture.

Notice how on the main character is sharp.The foreground and background are out of focus. Canon 350D (Rebel XT) with 17-85 IS lens. ISO 800 - 1/160@F7.1 Focal length 59mm (~90 equivalent)

Both the foreground flowers and house in the background are relatively sharp. Canon 350D (Rebel XT) with 17-85 IS lens.ISO 400 - 1/250@F10 Focal length = 17 mm (~28 mm equivalent)
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* All elements of exposure work together. *
On to Page two - Shutter speed or timing.
© Richard Taylor 2007