Number of available lenses is a big decision factor while choosing your interchangeable lens camera. When we look at the available lenses for these two cameras, we see that Nikon D80 has an advantage over Pentax K100D S. There are 309 lenses for Nikon D80's Nikon F mount, on the other hand there are only 155 lenses for Pentax K100D S's Pentax KAF2 lens mount.
Another important factor is the availability of image stabilization. Pentax K100D S has a big advantage in this regard because it has a sensor based image stabilization which means that all the lenses mounted to this body will be stabilized. On the other hand, Nikon D80 doesn't have this feature so you have to buy a lens with optical stabilization feature. Currently there are 106 lenses for Nikon F mount with Optical Image Stabilization features.
||# of Nikon D80 Lenses
||# of Pentax K100D S Lenses
|Wideangle Fisheye Prime
|Perspective Control Prime
|Telephoto Mirror Prime
Now let's compare some sample lenses from each mount with typical Focal ranges for Nikon D80 and Pentax K100D S to see how these lenses compares:
Fast Standard Zoom Lenses
Fast Tele Zoom Equivalent Lenses
Fast Normal Prime Equivalent Lenses
Fast Wideangle Zoom Equivalent Lenses
24-105mm f4 Equivalent Lenses
Super-Tele Zoom Equivalent Lenses