Originally posted by ctt Just trying it out, I put the biggest extension tube on and dialed my macro lens to 5.6 apt. (my then focused and mashed the green button. 2" F-- comes up, but when I take picture, it's not even close to right exposure. What am I doing wrong??
You did nothing wrong, maybe except for trusting Pentax with lens compatibility
What camera body are you using? I assume it's one of the K-series....
What you experienced is a case of metering problem with manual lenses. This problem is well-known. Please do a search on this forum for many threads relating to this issue.
The smaller aperture settings, the more pronounced the problem.
With the extension tube and macro setting, the effective aperture is several times smaller than the setting on the lens. For example, even without extension tube, at 1:1 magnification, a setting of F/5.6 on my 55mm macro lens actually means F/11 (2X slower). With extension tube, F/5.6 setting may be actually as small as F/22 effective.
In my experience, at F/11 and smaller apertures, the metering error on a K10K can be 2X or 3X toward overexposure. So when the body set shutter speed at 2", the correct one can be 1/4".
The only solution to this metering problem that I know of (and have verified with both of my K10D bodies) is to replace the stock LI-80 focusing screen with an LI-60 or LL-60 screen (or any other -60 series). The -60 screens are the ones for *ist camera bodies.