Originally posted by David Cook Is there is a situation when you would change aperture manually on this lens and if not why have the ability to do so?
Any time there is something between the lens and the camera body that does not permit the aperture lever to be activated. Extension tubes (hollow tubes with the required mounts on each end) to increase the magnification by moving the lens away from the camera are the only examples I can think of, as far as I know, compatible tele-convertors have the necessary linkage. If you have a Pentax film camera that isn't capable of automatically setting aperture (say a K1000) then only lenses with aperture rings will work and even with cameras such as the Program Plus, if you want to manually set the aperture, you have to do it with the aperture ring (those cameras open up the aperture for metering, but close it down to the set aperture when the shutter is released).