Hello,
Thanks chalion. Here is some useful info from Pentax's Support Site;
Pentax K-mount, M-series and S (screw) mount lenses without auto-aperture control (an “A” setting on the aperture ring) can be used in Manual exposure mode using stop-down metering and manual focus. This is the exposure mode which will give accurate exposures when using these older lenses on our digital SLRs. If older lenses without an "A" setting on the aperture ring are used in Av (Aperture Priority) Mode, an exposure error may occur. Note: Using Pentax S (screw) mount lenses on a Pentax DSLR requires the use of a Pentax Mount Adapter B. Using Older Lenses on Pentax K10D, K200D, K20D | Pentax Support Using Older Lenses with the PENTAX K-x | Pentax Support
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