problems with New Sigma Hyperzoom and old SF7

Hello eyeryone,

Glad I located this forum as I have just purchased (over the Net) a new 28-200 Sigma Hyperzoom lens for my relatively old Pentax SF7. The mount was right and it fit but it doesn't seem to be working properly. In auto mode upon clicking the shutter button the viewfinder goes black for about 2 seconds and then the camera fires. If I use manual focus I can sometimes get the shutter to function right but it's very hit or miss. This lens does not have a motor and uses internal focusing...could this be the problem? It's supposed to work with Pentax AF cameras but maybe not one this old. I have a Tamron 28-80 that works fine and the camera shoots great pics but I was hoping to get a great "all-round" lens. Any thoughts or suggestions will be much appreciated. Thanks.

I found that one of my old Sigma zooms would not work at all with a Pentax SFx, although it would work with the Z1-P. There are a number of compatibility problems with Sigma lenses.
G