I love macro photography but don't have the money to buy a dedicated macro lens. I've been using a 210/5.6 Symmar-S with what seem to be fine results. I've always heard that macro lenses are optimized for higher reproduction ratios (RR), but I don't understand why. Does it matter if your subject is planar or not? I've read that process/copy lenses are better for flat subjects but wonder whether they'd be any better than a normal lens for flower (3D) macro work. How can a lens be "optimized" for infinity to 1:10, or 1:10 to 2:1?
See if my simple logic about optics is correct. When you photograph with a lens that produces an image circle that just barely covers the film, you're using all the glass in the lens (ie. the edges as well as the center). Since the edges are usually not as sharp, resolution suffers a bit. With higher magnification (say 1:1 since this is what I often shoot at), you're using much less of the periphery of the lens elements and, therefore, more of the "sweet spot" (ie. the center of the glass) which should result an image on the film that is sharper corner-to-corner and with less distortion than you would have made at infinity. If my logic is correct, ANY lens should make a great macro lens since, at high RR, you're using more of the lens' sweet spot.
If someone could comment on my logic and clarify why and when macro lenses are better, I'd greatly appreciate it. (I have a rudimentary understanding of optics and college physics, but I guess the simpler the better.)
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