A few months ago, after much thought and reading of reviews, etc., I bought a Canon 24-105 f4L lens to use primarily on a 450D (Rebel XSi). I'll make a long story short: I didn't set out to critique the lens, but in the process of figuring out what turned out to be a camera problem, I spent a fair amount of time pixel-peeping at test shots (dollar bill and bright paper taped to a door, camera levelled on tripod, mirror locked up, IS off.....). Inevitably, I did some lens comparisons. What I see is virtually no difference between this lens (24-105L) and the Canon 28-135 IS. I see vanishingly tiny differences in color and brightness (couldn't say one was better than the other, just different), but if anything the 28-135 has a miniscule edge in small-detail sharpness. Suffice to say I'd think they were the same shot unless seen side by side at 100%. So I'm inclined to conclude that the value of this lens (in terms of IQ, that is - not build, durability, aperture at the long end, etc.) is wasted on a cropped-frame camera. Would others agree, or am I missing something, or just crazy?
Thanks for ideas,
Greg