This table shows the horizontal Field of View for the most common focal lengths for the various sensor and film formats in the Pentax camera line-up.

As an example, a 24mm lens has a horizontal field of view of 53.1 degrees on an APS-C camera like the K-7.

To get a similar Field of View on a 24x36mm camera you'd need a 35mm lens (gives a 54.4 degrees FoV as per the table, close enough) whereas on a 645 camera you'd need a 55mm lens (gives a 54 degrees FoV).



For an explanation of crop factor and field of view check out this article:

Crop Factor, Focal Length and Field of View