problem with focus on sigma lens olymous om 10 camera (focus "dot" inside the viewer gets half dark or black) In: Cameras Posted May 17, 2014 Hi guys, I've bought an Olympus OM10 film camera with a 50mm lens. Because I wanted a zoom lens to use with it I got through ebay a sigma 28-80mm f 3.5-4.5 UC zoom. I have just received the lens and I notice that sometimes half of the focus aim inside the viewer gets darker or black. If I'm not wrong it happend too with 50mm lens but then during my photoshots it never happened again. Does anybody knows why this happen?may it be because the camera had no film inside (I was just trying the lens) or because I was in a poor light environment? Thanks for everything guys!