I own an om1 along with a 50, 28 and 200mm lens. When I close the aperture on my 50mm the aperture ring runs smoothly. When opening aperture however, it's difficult to turn the aperture ring as if there was a spring causing resistance. This only occurs with my 50mm. Is this a design feature or a mechanical failure? I've tested the camera using bulb mode and the aperture blades move fine.