Dave Quinn , Jan 19, 2010; 02:44 a.m.
I think we need more information and a specific example to look at.
In general though lens quality is everything: a prime (fixed) lens will give you the sharpest results. Even cheap prime lenses offer very good quality. I did a 50mm lens test a while back and was quite surprised just how good an $80 50mm lens was. Easily as good as my $800+ 28-70/f2.8L pro zoom and in a different league to cheaper zooms (I know those are Canon examples, but the principle will be true for Nikon too).