On your original exam you worked with the logarithmic equati

On your original exam, you worked with the logarithmic equation for the exposure value, EV, of a photograph: EV = log_2 f^2/t (where t is time in seconds that the shutter was open and f is the value of the f-stop the picture was taken at). Rewrite your expanded formula from the original exam using the change-of-base formula. Emma takes a picture of her friend\'s track meet with a shutter speed of 1/250 second at f/8. She likes the exposure of this picture, but her friend, running a lap, is blurred. Emma resets her camera with a shutter speed one fourth as long to get a better picture on the next lap. What f-stop should she use on her next picture?

Solution

22. EV = log₂(f^2/t)

Using the log formula : log(a/b) = loga -logb

EV = log₂(f^2) -log₂(t)

Using the cahnge of base formula : log₂(a) = log₁₀a/log₁₀2

Converting the EV formula to the base of 10

EV = logf^2/log2 - logt/log2

=(1/log2 { logf^2 - logt }

Finally use : loga^x = x*loga

E =  { 2logf - logt }/ log2