that's one of the problems with small sensor digital - no fast ultrawide lenses can really stand up to lenses of longer focal lengths when comparing image quality. The smaller the sensor, the more important it is to have a high quality image to support the degree of magnification required even for 3x5 prints. For a small aperture, not such a big deal, but larger apertures introduce all kinds of failings, from distortion to vignetting to ridiculous expense. And to get anything like a "medium wide" on a small digital sensor, you need an extremely short focal length.