First, I would like to thank everyone for answers.
Make sure the zoom is smooth. It might have loosened up a bit with use, but it shouldn't stick at any one point, even slightly.
What counts as sticking? If it turns easier at one interval and harder at the other end, is it considered sticking?
What could be bad if it sticks?
Check to make sure that the aperture blades stop down quickly and are free of oil, and shine a flashlight through the lens to check for fungus and dust, and you should be ok.
Aperture seemed to be ok, I tested in all f/stops on my camera.
To what extent does dust degrade image quality? There were a tiny piece of dust or two that were visible inside the lens.
Also there was a small scratch on the rear glass, though it was visible only when looking from a low angle.
How much could the small scratch affect the image quality?
Thanks a lot!
Bao
