Originally posted by Lowell Goudge This site works for some lenses, but not for my two Pentax-F primes (F28/2.8 and F50/1.7). These lenses both apparently have the same contact arrangement when I look at the mounts. I suspect they are wired differently internally to agree with the patterns listed, but I'd have to check with an ohmmeter. The OP's lens pattern looks like a lens that goes from f4.5 to f32, or I'm getting something wrong.
Back to the subject at hand, you should be able to see if your 16-45 set at 28mm and f4 has the same exposure as the prime lens at f4. You should definitely try using the DOF preview lever as I suggested above, in Av mode, let's say set at f8 on the camera, with the lens aperture ring set to A. Then move the aperture ring off of A to f8, switch to M mode and try the DOF preview again. The lens should stop down the same amount both times.