I'm thinking of getting a EF 100f/2.8 L macro IS USM lens, because I want to shoot macro photo's. Before I plunk down my hard earned dough, I wanted to ask a question. I am going to use it on my 40D, which as you all know is a crop body. I do grasp the smaller sensor/crop vs larger sensor/FF concept. What I was wondering is, when using the 100 L lens on my 40D, I multiply the 1.6 crop factor to the 100mm lens and get 160mm. Is that desireable? When/if I get a FF body, and mount that same 100 macro L lens to it, since there will be no crop factor to apply, will I be disappointed in the focal length of my 100mm lens? Will that be a big adjustment? Is there some factor I am over looking that mitigates the loss of 60mm focal length? Something else... why do you apply the 1.6 crop factor to an EF-S lens when it was designed for crop body cameras?