Cinematography Resources

Math Fundamentals

Ratios

Ratio is needed for lighting and lensing.

Ratios are used in lighting to compare different sources and their output. For example, measuring how much fill you’re using in comparison to your key light for a particular scene, so if you can more easily recreate or adjust it.

RATIO IS A COMPARISON

Ratios can be written in three forms:

1. word form: 5 to 6
2. colon: 5:6
3. fraction form: 5/6

*Ratios should always be simplified (4 to 8 becomes 1 to 2)*

RATIO EXAMPLE
Question: There are 12 girls and 14 boys at the school. What is the ratio of girls to total number of students?
Answer: 6 to 13, 6:13 or 6/13

*Make sure to know whether you’re comparing a part to the whole, or another part.*

Simplifying Fractions

To simplify a fraction simply divide both numbers by their greatest common factor.

Greatest common factor is the largest number that is divisible by both the numerator and denominator.

SIMPLIFYING EXAMPLES
Easy Question: Simplify 122/568
To get the largest factor for 122 and 568 fast, we can divide them by their smallest prime number, i.e. 2, if 2 is not a factor move to 3 until a factor for both IS reached.
So we divide 122 and 568 by 2, giving us 61 and 284.

Answer: 61/284

Easy Question: Simplify 6,437/29,555

First find the smallest prime number divisible by both.

Answer: Already simplified!

In order to simplify a fraction there must be:

A number that will divide evenly into both the numerator and denominator so it can be reduced, or
The numerator must be greater than the denominator, (an improper fraction), so it can be converted to a mixed number.

RATIO EXAMPLE
Question: There are 12 girls and 14 boys at the school. What is the ratio of girls to total number of students?
Answer: 6 to 13, 6:13 or 6/13

*Make sure to know whether you’re comparing a part to the whole, or another part.*

Math Fundamentals

Table of Contents

Ratios

Simplifying Fractions