For some strange reason I'm considering the purchase of a Leica IIIF camera. I do own a 50mm F2 Summar lens, which I occasionally use on my M6 as this lens actually gives the Leica Glow when shot wide open. But now I want to use it on a screw mount camera, a device I've always admired. The example I'm considering, however, seems to run slow at the lower shutter speeds. How easy or difficult is this to set right? Can it be fixed?