Sigma 100-300 f/4 EX IF

I've heard that the diaphragm of this lens (Sigma 100-300 f/4 EX IF, without DG) doesn't work with digital cameras and I wondered if this is true for Pentax. Does anybody have experience with this lens (not the new DG version)?

I don't know this lens but if it has no 'A' setting on the aperture ring then that may be partly true. It will behave in much the same way as pre 'A' series lenses and will require stop-down metering with the camera set to Manual exposure mode. It'll stay wide open in all other modes.

I have the lens and it works perfectly well on the K10D, the IF was the version pre-DG, and AFAIK all EX lenses are AF.

Fabulous lens.