Tuesday 3 July 2007

Exposure Cheat Sheet

Just lately I have been doing an awful lot of training with people and I have often emailed them a quick summary (a cheat sheet) of what they have learnt. I thought I would stick it here so I can get to it when I need it and it might help folks.

Depth of field.

Definition - "the amount of an image that is acceptably sharp"
  • Increasing the f number (decreasing the size of the aperture) increases dof.
  • Reducing the distance to the thing you are focusing on reduces dof
  • The longer the focal length of your lens the less dof you have.

  • The size of the hole you are taking the picture through - the bigger the hole the shorter the shutter speed.
  • Its a fraction so the higher the number the smaller the hole.
  • When you look through the viewfinder you see it wide open (lowest f number).
  • Dof preview shows you the effect of aperture.

Shutter Speed
  • Increasing the f number in a given situation increase the shutter speed.
  • The rule of thumb for hand-holding is that you can hold at a shutter speed of 1/the focal length.
  • So a 100mm lens can be held at 1/100th of a second or faster - i.e. the number at the bottom of the display should be 100 or greater.
  • Shutter speeds followed by “ are in seconds - you ain’t going to handhold those whatever lens you have on!

  • Increasing the iso increases the sensitivity of the sensor (film) and so means the exposure takes less time.
  • ISO 100,200 & 400 are virtually noiseless. After this noise starts to increase.

Shows the distribution of light in your image from black on the left to white on the right. An evenly distributed graph is generally ideal. Peaks at the extreme left indicate blocking up of the shadows, peaks to the extreme right (and flashing highlights indicate burnt out highlights.

You can either recompose or use exposure compensation to correct.

Book Recommendation: Understanding Exposure

Related Posts

Shadows and Highlights
Preflight Check List

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