Over Christmas, I bought a non working Olympus OM 30 for £20 just to get a spare 50mm lens. When I got it home , the mirror was jammed half way up bit the lens appeared to have some sort of mark on it too. So I decided to leave it in a drawer at my Mother's house and quietly forget about it. Anyway. On Saturday, myself, my sister and my mother (all film photographers, by the way) went to London (UK) to see the 'Ansel Adams, from the mountains to the sea' at the National Maritime Museum in Greenwich, which meant staying at my mother's house over the weekend. On Sunday, I found a load of LR44 button batteries going to £1 in a local shop and decided at that price I had little to loose. I went home, put them in the camera and switched it on. The shutter fired, the mirror dropped and it began making odd noises at me. The problem was simply battery failure. But it leaves me with two questions. Firstly there's this odd F4 F2 dial under the lens mount. What is it for? And secondly, the mark on the lens I now think is just dirt inside. But it doesn't stop down properly. So is it likely that the cost of repairing the lens (an Olympus F.Zuiko 30mm) likely to be more than the cost of replacing it? Chris B.