I've heard claims ranging from "higher-quality lenses only make a noticeable difference for scientific applications and super-huge prints," to "even the difference between high-quality and uber-high-quality lenses can be seen with the naked eye on 6x10 prints"
Before I sell my house so I can take amazing pictures from a cardboard box, I'd like to actually see the difference. However, all the examples I've found compare photos not only from different lens, but also with different cameras/scenes/photographers!
Are there any examples of the same scene, with the exact same settings on the same camera, taken with multiple lenses (of differing quality/price)? Multiple comparisons with different scenes/cameras (especially cameras of different qualities) would be preferable, to eliminate any variables. I'd also prefer a non-biased source (so, not the lens-manufacturer).
I'd also be interested in comparing telephoto to zoom+teleconverter (of the same quality, focal-length etc.), or comparing zoom to fixed-length... but perhaps those are asking too much :)