LiamG: you have provided the BEST answer so far. At least with a 28-80mm you would get the normal 50. Surprisingly, von Hoegh, the modern zooms are VERY sharp; (but slow, true). Still, it is a bit of an answer. I would really like to put a Minolta MC on a Nikon, though. I could slightly increase its infinity to match the 46.5mm distance needed. - David Lyga
Their sharpness may be comparable to some primes, but they are slower, bulkier, heavier, more expensive. To me they are a compromise at best. I don't like them and don't use them. YMMV.