1.Could anybody tell me what extension tube I need to get a 1:1 ratio with either a 127mm and a 65mm lens on my Mamiya RB67? 2.Are there any cons with using a 65mm lens as a close up lens with the extension tubes? 3. Are the extension tubes for a RB67 and RB67 pro SD different? 4. Does anybody know where I may purchase some used extension tubes? Thanks Chris Stevens.