Warmup 74 (March 21)

When you change the camera setting by moving the APERTURE from, say, f/4 to f/5.6 we say you have closed down the aperture by ONE STOP. A STOP is a unit equivalent to 1/2 the light of the previous setting. It works the same for SHUTTER SPEED:

1/2 - 1/4 - 1/8 - 1/15 - 1/30 -1/60 - 1/125 - 1/250

Each step is considered ONE STOP of light.

Look at the photo below. Try to guess how it was taken, especially, what do you think the shutter speed was?