Quote Originally Posted by cowanw View Post
I suspect the difference is that 1:1 in 35mm involves a subject of 1 inch and 1:1 in 4x5 involves a subject of 4-5 inches. One view of the issue is that magnification is the same and the other view is that subject size stays the same.
in practical terms, if you want to frame your subject (of any size) a certain way in the final image, the larger your film format is, the higher the magnification needs to be and the more light you need above what your meter says you need, except when focused at infinity because that's the point where your lens' f-stops are actually what they say they are and will match your meter.