larryepage wrote:
See if the aperture lever on the lens freely moves and closes the aperture down. One possibility is gummed up lubricant on the iris blades causing everything to stick in the open position. I have had this happen to a couple of older lenses by other manufacturers. If that's what's happening, a clean and lube of the lens should fix the problem.
This is a distinct possibility especially if the lens has been over heated such as being left in a hot car. The lubricant runs and gets on the blades and when it cools causes them to stick.