Originally posted by jackbullet My apologies oh great one!!!
You have to excuse us old guys!
This and similar questions come up frequently and it is tempting to get cranky at times.
When the camera asks for focal length with a non-AF lens, it stores that information for use with the shake reduction system (SR). How SR is applied is dependent, in part, on the focal length of the lens...specifically the lens' magnification.
Mounting a 50mm lens on a camera with a APS-C sensor does not change the optical qualities of the lens. A 50mm lens regardless of whether it was made for 35mm film or APS-C sensor will still have focal length of 50mm and the same magnification. Since it is asking for the focal length, you should enter the focal length.
So, what about the "crop factor". In simplest terms, the "crop factor" is just a convenience calculation that allows a person familiar with the 35mm format to know what field of view (FOV) they can expect on the smaller APS-C sensor. It is called the "crop factor" because using a smaller sensor is equivalent to the process of cropping an image to a smaller size in software or in the darkroom. Make a print from a 35mm negative, trim a third from length and width and you have the same subject as viewed on APS-C.
This probably is as clear as mud, but it is a try.
Steve