Originally posted by 3party 1. If I use an older Pentax lens, such as my f/1.8 85mm SMC on my K-5, is there any part of the metering that I can use?
Assuming that your is what we call K-series, which means a PK bayonet mount with mechanical aperture linkage, and no series prefix on the lens (ie it's not SMC-M or SMC-A, just SMC) then you have two basic metering modes. First, set the menu item USING APERTURE RING to PERMITTED. Now you can use either M(manual) mode, with the Green button for stop-down metering and exposure, or any Auto mode (this defaults to Av), where the lens will stay wide-open and the camera will meter and expose automatically.
Quote: 2. As a practical matter, how will the fact that the lens was designed for 24 x 36 affect its performance on the K-5 ?
The smaller crop of the APS-C sensor means that problematic image edge areas are discarded. No edge weakness, no vignetting; you're getting the projected image's "sweet zone". DOF *is* affected. If I'm shooting a FF lens on my K20D and I have the aperture set to f/11, I'll read the lens' DOF scale at the f/8 marks.