18 MM
55 MM
What I noticed when shooting the same photo at different photo focal lengths: I could immediatly tell that the light and exposure were differant. The photo at 55 mm was a little less exposed. It was also interesting in noticing that when the photo had artificial zoom, in other words when you are not actually close to the subject, the edge of the photo seemed to be a little warped. The shapes were "flattened" or mashed and basically fatter. I would say that you would REALLY care about this when you are going for subtlties within the picture.