Can people give me some advice on which extension tube to buy for a manual focus AIS lens? I don't need the electronic contacts for autofocus, but I would like to have high quality build for the tube between my lens and my camera. Right now, it looks like like the Nikon PK13 is what I want, but I'm not sure if I will lose metering information? I would not prefer the Kenko tubes because a quick search of previous threads said that the tubes are made of plastic, and I don't need the electronic contacts for autofocus. Any suggestions or encouragement for the Nikon PK13 appreciated - thanks!