35mm film: 35mm wide
Nikon D-SLR Sensor:
23.6mm wide
So the ratio of 35mm film to a Nikon D-SLR = 35/23.6 = 1.48 = ~1.5
What you have with a D-SLR is a "sensor crop", basically, for the same lens, the angle that is covered is smaller with a D-SLR because the sensor is smaller than a 35mm film frame.
Basically if you start from the same vertex, the angle that is available to be included in the frame is smaller with a D-SLR than a 35mm film camera, because the sensor is smaller.
As a result, the lens is effectively "magnified" by a factor of 1.5 (Nikon) or 1.6 (some Canon).
What does this really mean to you?
1) For Telephoto, a d-slr is more cost effective to achieve the same image size/crop because the sensor size means that where a 200mm lens shot with 35mm would be 200mm, a 200mm lens shot on a Nikon D-SLR would effectively be a 300mm in terms of what would appear in the framing.
2) D-SLR users get SCREWED when it comes to wide angle, because even 12mm shot on a D-SLR would have effectively been 18mm on film.
Make sense?
