> Tha answer is to be found (of course) on Boz's web page: > > http://www.bdimitrov.de/kmp/extras/K-mount/Ka.html > > "Displaying Aperture in the viewfinder > > "In the Tv and P operating modes the body decides how many f-stops the lens > will be closed down during the exposure. Consequently, knowing the narrowest > aperture and the number of f-stops allows the higher-end bodies to calculate > and display the selected f-stop. > > "But why does this not happen in the M and Av modes? After all, knowing the > positions of its stop-down coupler, the body should be able to calculate how > many f-stops the lens is closed down. Knowing the narrowest aperture and the > number of f-stops, the body could calculate the widest aperture, and then > the manually-selected f-stop. Yes, but only for prime lenses! > Variable-aperture zooms have fixed contact patterns, and can therefore only > indicate a fixed aperture range. In this case, the incorrect f-stop may be > displayed in the viewfinder, and I guess that because of this, Pentax left > the feature completely out. Note that due to the TTL exposure metering, the > film will be exposed properly regardless of the fact that the f-stop's > numerical value may be calculated incorrectly."
Hmm...I'm almost asleep, but the 'Yes, but only for prime lenses!' Jumps out at me. Does that mean I should get a display, and only the 'A' Zooms don't? I'm not reading it well enough, feel free to correct me. I'm just wondering why there is an electrical contact on the lens. > -- > Mark Roberts > Photography and writing > www.robertstech.com > >
