Aspect Ratio definition

The ratio of the frame.  Usually aspect ratios are shortened to remove the “- to 1” because they assume the ratio will always be in relation to 1.  So a ratio of “1.85 to 1” is just known as “1.85.”  A squarish image is taken by cameras in 16mm and 35mm with an aspect ratio of 1.33.  In 35mm, this ratio is called the Academy Aperture.  Frequently in 35mm the image is shot with this ratio and then masked in the projector, which will then create a wider image.  In the USA, this is 1.85, and in Europe this is 1.66.