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Pixie dust...
I think that it's often hard to show in a couple snaps in a forum, because you have to go through a lot of iterations with a lens in comparison with other lenses in the same shooting situations before you start to notice a difference.
Really, with telephoto and normal, what it usually is that strikes people is a high central sharpness, often a disparity with the edge sharpness (helps the '3-d' aspect,) nice contrast and microcontast (different - look it up, interesting concept), nice bokeh and a non-jarring OOF transition. All of these things can be measured individually with the right tests, but taken together they bring an effect that's very pleasing, sometimes surprising....
pixie dust. And it's pretty subjective too, so don't epect to always see it in examples unless you can look through someone else's eyes. But when the experience happens to you, you know it and it brings a lot of fun to photography.
With wide-angle, it's usually just sharpness and incredible color transmition and general contrast. I think that's why the DA 12-24 and DA 15ltd take so many great images - your colors just blow up, it's very sharp, and incidental light on the front element doesn't kill the contrast. Modern coatings play a big part of the WA pixie dust.
Anyway, my most dusted lens IMO is my 77ltd. I can just point it at anything and it looks interesting.
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