A couple of days ago I experimented with the AF 1.7TC, the autofocus teleconverter, on the *istD. My Pentax lenses worked fine, but my Sigma EX 70-200/2.8 did not work well with the TC. On full opening, the aperture reported was f/2.8. When stopped down, however, I could select f/40. That's 2/3 stops more than the lens supports on it's own.
Today took readings with MZ-S, and the same happens there.
Also, exposure was way off at some apertures It overexposed badly on full opening, then worked fine at f/4 to f/16, and then gradually began to overexpose again. At f/32 it was at least as bad as at f/2.8, and the "f/40" was useless.
Anyone else had the same experiences?
Jostein
