I was out today at Teignmouth, shooting the last day of the Lark national championships. Not a spectacular day - rather cloudy and a light and very shifty wind. I was using the usual combination of K-7/50-200 and Canon 40D with a variety of lenses: 400 f5.6L, 70-200 f4L with 1.4 extender and Sigma 10-20.
Towards the end of the afternoon I noticed in the K-7 viewfinder "F - - -" which seemed to indicate an indeterminate aperture setting. I guessed the problem was the connection between camera body and lens. After detaching the lens and wiping the contacts on both camera body and lens, the problem was solved.