I've got an older (1970's) Pentax SLR. I was in the woods today trying to get pictures of a rabbit. When I pushed the shutter release it took the picture but the mirror got stuck and wouldn't go back down. I took two or three more shots of whatever and it went down, but got stuck repeatedly and I ended up wasting half of my film trying to make it work. Is there any way to fix this without having to take it in?