Understanding Contrast Ratios

If you're looking to acquire the most amount of creative control over your images, be it for photography or cinematography - then you need to know contrast ratios down cold. There's a lot of mis-information out there and Vistek video producer Dale Sood is going to clear it up and give you the full down-low on on contrast ratios.

Here are the three (albeit slightly complex) calculations for contrast ratios:

WHOLE STOPS:

2(to the power of X) = STOP DIFFERENCE: (eg. 3)
Example calculation: 2(to the power of 3) or 2x2x2 = 8 so 8:1

FRACTIONS OF A STOP

SAMPLE: Key is f8, fill is 2.8 2/3
1. Determine your stop difference by counting how many stops
between your key and fill. The difference is 2 1/3
2. Add the whole number (2) with the fraction converted to a decimal:
1 divided by 3 = 0.333333 + 2 = 2.333333
3. Multiply your answer by 0.301: 2.333333 x 0.301 = 0.702333
4. Take the anti-log of the result using the 10x button on a calculator. Answer: 5.0388709 = 5:1 ratio

EXPOSURE WHEN THE RATIO IS KNOWN

Determine your stop difference. If it's whole stops, then it's quite easy, just
halve the values to zero. Eg: 64:1, so 64-32-16-8-4-2-1 = 5 Stops from key.

However, if using more complex ratios like 40:1, this formula can be used:

1. Take the Log10 (10x) of the higher value (40)
Log(40) = 1.602059991327962
2. Divide your Log10 answer by 0.301 = 5.322 = 5 1/3 of a stop difference.
3. Choose a key and fill level that give you a 5 1/3 difference