said by 29886823:Ok, what he said
You say that: "Most of us with SLRs have crop sensors so our 50's are really 80 (on Canon) or 75 (on Nikon). Does that help?"
No it doesn't. 50mm lenses are 50mm lenses. All the crop factor does is change the field of view.
For this exercise to work, just set your focal length to 50mm (for zooms) on crop cameras; if you have a prime 50mm just use it on either full frame or crop cameras.
The only important thing is that your lens focal length is 50mm.