Aspect Ratio
The aspect ratio of an image is the ratio of its width to its height. It is commonly expressed as two numbers separated by a colon, as in 16:9. For an x:y aspect ratio, the image is x units wide and y units high. Widely used aspect ratios include 1.85:1 and 2.39:1.
Sometimes aspect ratios will be referenced as a fraction that has been reduced. For example 16:9 may be expressed as 1.77:1. This is because 16/9 = 1.77.
4:3 or 1.33
This format is almost nearly a square and is often times used for creating a period look pre 2000. It was the standard for TV up until the late 1990s before it was replaced by 1.77:1 or widescreen format.
16:9 or 1.77
Can also be referred to as 1.77:1. This is the format that we know as widescreen and is the standard aspect ratio for cinema.
2.39:1
Also known as Cinemascope, this wider aspect ratio is best for showing wide vistas or scenes with lots of characters. For example an ensemble piece might lend itself to a wide screen format as it allows you to have 4 characters in the frame at once very easily, where as with a more standard aspect ratio you would be forced to do a much wider shot to show that many characters.
