The older version (the size of the 40-150mm f2.8) with newer coatings, not the newer stabilized lens (the same size as Olympus 35-100mm f2.0). Cheap at twice the price Wide open at 150mm. Do people actually take pictures of birds wide open? Wide open at 80mmish. Just imagine that this is a person instead of a tree: one eye will be in focus, the other eye, both ears, and nose are going to be out of focus. Wide open at 50mm Stick torture test, there's pretty heavy longitudinal CA seen as green fringing in the out of focus areas. 90mm ish stopped down to f/5.6 The limit to sharpness is going to be a combination of mirage due to it being a 40c day and me on my toes holding the camera up high in the air to get it above a tree (the key point to me was that I could actually do so, it's nice and small/light). I think I'll keep it, it's not perfect optically however it's a pretty reasonable compromise given the price paid (USD$230).