The 35mm lens will have a FFE of 52.5mm. Focal length doesn’t change.
What’s really happening is “focal length” is being used as a proxy for “angle of view”. So the 35mm lens on crop sensor has the same angle of view as a 50mm lens on full frame, which is about 40˚. People relate to 50mm more easily than 40˚.
It actually goes further: a 50mm lens on full frame is about the same as a 150mm lens on 4x5, a 210mm on 5x7 and a 300mm lens on 8x10. On each of those formats the angle of view is about the same so the picture will turn out with about the same framing.
The 35mm lens will have a FFE of 52.5mm. Focal length doesn’t change.
What’s really happening is “focal length” is being used as a proxy for “angle of view”. So the 35mm lens on crop sensor has the same angle of view as a 50mm lens on full frame, which is about 40˚. People relate to 50mm more easily than 40˚.
It actually goes further: a 50mm lens on full frame is about the same as a 150mm lens on 4x5, a 210mm on 5x7 and a 300mm lens on 8x10. On each of those formats the angle of view is about the same so the picture will turn out with about the same framing.