Pentax K10D Operating Manual page 17

The captured area (view angle) will differ between the q and 35 mm SLR
cameras even if the same lens is used because the format size for 35 mm film
and CCD are different.
Sizes for 35 mm film and CCD
35 mm film
q CCD : 23.5×15.7 mm
Angles of view being equal, the focal length of a lens used with a 35 mm camera
must be approximately 1.5 times longer than that of q. To obtain an angle of
view framing the same area, divide the focal length of the 35 mm lens by 1.5.
Example) To capture the same image as a 150 mm lens attached to a 35 mm
camera
150÷1.5=100
Use a 100 mm lens with the q.
Inversely, multiply the focal length of the lens used with q by 1.5 to
determine the focal length for 35 mm cameras.
Example) If 300 mm lens is used with q
300×1.5=450
Focal length is equivalent to a 450 mm lens on a 35 mm camera.
: 36×24 mm
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