I was out shooting today - a bright sunny day , all was good, changed lenses a few times, still good. Then, the viewfinder got darker, the speed, even at ISO 400, would not go above (i.e., faster than) 1/20 or 1/30s, even when pointed at something bright, like a cloud. I changed lenses to check, same thing. Then changed batteries, no change in viewfinder or speed. I checked the contacts, and wiped them off. My settings were all as usual. I'm stumped. Anyone had a similar problem? I like the camera and use it every day, so I'm quite used to what is normal. Any suggestions would be appreciated.