Sony SLT-A58 - Manual (Page 87)

Specifications
Others
87 GB
On focal length
The picture angle of this camera is narrower than that of a 35 mm-format
camera. You can find the approximate equivalent of the focal length of a 35 mm-
format camera and shoot with the same picture angle by increasing the focal
length of your lens by half.
For example, by using a 50 mm lens, you can get the approximate equivalent of
a 75 mm lens on a 35 mm-format camera.