Originally posted by Pepe Guitarra I have not been able to use extension tubes or bellows with my Pentax K-x. It seems that I loose lots of light and cannot focus. I set the aperture in PERMITTED, but still do not see. Is there anything I can do? I have successfully used the converter 2x with my Pentax M 50mm f4 to get a nice macro, but with the 31 mm extension I cannot focus and it is dark. Can you comment please?
With an ordinary bellows or cheap macro tubes, your M-type lens should be uncoupled from aperture control, and the lens should act as a preset -- open the aperture to f/4 for most light. More expensive macro tubes have a mechanical linkage for the aperture, and you should be able to do stop-down metering and exposures in M(anual) mode.
A 31mm tube on a 50mm lens should only reduce light by a little over 1 f-stop -- it shouldn't be dark, so I can only suggest that you check that the aperture is wide open and your subject is well-lit.
As for focus: On any extension, the small throw of the lens focusing mechanism doesn't amount to much. With bellows, you use the bellows for focusing , not the lens. With tubes, you generally move the whole camera-lens system or the subject back and forth to achieve focus. So don't worry that the lens doesn't focus -- it doesn't matter.
Good luck!