I still don't fully understand it. Here is a site that helps to explain the multiplication factor: http://www.luminous-landscape.com/tutorials/understanding-series/dslr-mag.shtml
What is confusing from this article is,
"Crop is a fairly good term the imaging area is physically smaller. Less of the image circle projected by the lens is used, therefore it is a crop. The image remains the same size at the film plane for a given lens and subject distance it is in no way magnified. It does, however, take up a larger proportion of the (smaller) frame and so it is easy to see why some people call it a magnifying effect. This is also why a tele lens appears so much more powerful the field or angle of view has been reduced. This is great for nature and sports photographers as the net result is more real pull than before with no trade off of maximum F Stop loss."
So is the image bigger because we are enlarging the smaller "film size" more? If I use a 300mm on a 35mm camera and then on a DSLR am I actually bringing the subject "closer"? If I am not actually bringing it "closer" does the enlargement end up having the same result of a longer lens? Sorry just thinking out loud.
It is all very confusing.