What is an aspect ratio?

Every photo or movie has an attribute called an Aspect Ratio. The aspect ratio is the relation between the horizontal and vertical sizes of the photo. To calculate the aspect ratio simple divide the width or a photo by its height. For example TV in normal mode has an aspect ratio of 4:3 or in other words if we were to divide the width of the screen by its height the result would be 4/3. TV in widescreen format on the other hand has an aspect ratio of 16:9.

When we take a photo with a camera light that travels through the lenses hits a sensor (a film in traditional cameras or a CCD in digital ones). The sensor in turn translates the light into a two dimensional photo. The sensor itself has physical attributes such as width, height, granularity (in films) and number of pixels (in digital CCD sensors).

The connection between an aspect ratio and photo printing

When photos are printed on paper the aspect ratio of the paper must be the same as the aspect ratio of the sensor that was used to take the photo. If the aspect ratios are different the result will be a blank area left on the paper or a stretched photo that fits the paper but distorts the objects in it.

Why does it happen? The answer is pretty simple. For the sake of explanation lets assume a photo sensor that is 6 inches wide and 4 inches high (real sensors are much smaller). Lets assume that we are trying to print the a photo taken with that sensor on a paper that is 4 inches high. If the paper width would be less than 6 inches we will have to crop part of the photo since there won