I've taken upwards of 50 exposures with my cheapo-used-sold-as-broken-parts-lens SMC Pentax-F f4-5.6 35-105mm, and it still seems to work just fine zooming, focusing, & using the "macro" feature manually. I'll keep my fingers crossed that not attempting to use its failing auto-focus system will keep it from totally wearing out or breaking anything that using it manually depends on. Sometimes it doesn't communicate its f-stop in a way that lets it display in my K10D, but in some of the camera modes it does. When it doesn't, it doesn't seem to throw off exposures.
I've been posting some of the pics from it in other threads, most of them at medium to wide apertures. Here are a few from a mostly small aperture excursion with the lens:
This is at f16. I really should have guessed that the hyperfocal point would have been closer to me than where I focused, but the eye really isn't drawn to notice that the nearest part of the rails are a bit blurry.
f22. Since there is hardly any wide-angledness in the lens's 35mm focal length when used on cropped sensor, it is a little surprising at first to find some bending of lines when one is as close to a building as one can get to frame it. This sort of distortion is much less, if one backs up and lowers the shooting angle and/or uses a slightly longer focal length. I can't get over the great color the lens has with the k10D.
f22.
All of these shots began as OOC jpegs with camera setting for Sharpness, Saturation, Contrast zeroed. Then I did a little post processing mainly to fine-tune exposure and highlight brightness. Some of that affects contrast. I didn't touch Sharpness or Saturation in PP.