I was just about to put a filter on my 1950's Sonnar 50/1.5 that I use with my Contax IIIa and I was convinced that the Zeiss 40.5mm filters I have would fit - but alas - they don't. The filters seems to small to fit the lens but I could had sworn that this lens took 40.5mm filters. <br><br> I also have an S1119 hood (that fits on the lens) and the filters can screw into the hood. <br>Am I wrong about the filter size on the Sonnar, is there a 'trick' to how to use them - or is maybe the lens that I have damaged in some way? <br> Thanks in advance.