Originally posted by Peter Zack First on a digital each lens will act as a longer lens. The sensor is smaller than film is. so any lens length is multiplied by 1.5
50mm= 75mm on film considered a normal lens and on a DSLR a mid length portrait lens. The version you have is a good but entry level lens. Still very sharp though.
That's not quite right. On a DSLR with an APS-C sensor, what you experience is a cropping of the image circle by a factor of 1.5 (actually 1.52, but who's counting
). Your 50mm lens does not instantly become a 75mm lens--there is no magnification of the image. What happens is you have a narrower field of view and are using a smaller portion of the lens circle. Some argue since you are cropping the view, you have the same effect as if you had a longer lens, but there is no optical magnification taking place.
Crop factor is an annoying thing because it doesn't help you in the long end and it definitely impairs you on the short end. Where a 24mm lens was once a decent wide-angle, you now need a 16mm or shorter to frame the same shot.
BTW, those old Pentax 50's are still very good performers if you don't mind using your camera in manual mode. The good thing about them is you will actually learn a few things about photography instead of just pointing and shooting with an auto-* lens.
Enjoy.