Focal Length and compression

On a recent location shoot of some family portraits, I played with varying focal length to control the background of the image. Increasing focal length compresses the apparent distance between subject and background, this I knew, but never before had I actually studied the effect in a single shoot.

In the shots I varied the distance between camera and subject according to focal length to keep the size of the subject in image constant. You can see how different the feel of each of the images below are. You can use this technique to control how dominant an object or landmark is in the background - or even compress it further with longer focal lengths to push it into abstraction.

Image 1

Focal Length =40mm Camera to subject distance=15ft

Image 2

Focal Length =150mm Camera to subject distance=75ft