This lens has a feature whose purpose escapes me, so I'm hoping one of you old-timers can give me a clue. There's a switch that locks the aperture ring, and it only is available at f/32. I'm guessing there's some purpose to it, but for the life of me I can't imagine why anyone would want to lock the aperture at f/32. Does anyone know? I won't be able to rest until this mystery is solved. Thanks in advance!