Originally posted by Alex00 Assuming dpreview did there tests correctly, dpreview shows the 15mm at any aparature suffers from sharpness compared to all three lenses sigma 10-20, pentax 12-24 and tamrom 10-24.
OK, *one* reviewer. The rest - including ones like photozone who can put up actual MTF numbers to back up their claims - all say otherwise.
And actually, I don't think dpreview says what you think they say. Here's a direct quote form the review:
"Compared to the Sigma 10-20mm F4-5.6 EX DC HSM (at 14mm), the 15mm F4 comes out on top; it's a hair sharper, and has lower distortion and falloff."
As compared to the Tokina or Tamron, obviously, they didn't test that on the same camera, so results are not directly comparable. Plus they also say:
"it shows distinct curvature of field, which causes problems with our (flat-field) chart tests at the shooting distance used (approx 2m). As with the Sigma, we have chosen to present data that is technically slightly rear-focused, and therefore gives a better impressions of the edge and corner sharpness at the expense of the centre"
So they are deliberately testing out of focus images, and *still* finding it comes out better than the Sigma; if it comes out ever so slightly worse than the Tokina or Tamron, that could be entirely due to the fact that they test OOF images from the Pentax.
In any case, the differences we are talking abut are miniscule and have no real world relevance. There would be no reason to choose the 15 for its marginally higher sharpness if the focal length isn't perfect for you; a zoom clearly makes more sense for people who don't mind the size or weight.