Thank you John, that has gone some way towards helping me with a solution. However since I first posted I have tried another lens - a 55 f1.8 K lens which was the original lens on my Pentax KX. I found that with both this and the Tokina I could not get either to stop down to the set aperture with the istDS Preview lever nor when an exposure was made. I am beginnig to wonder if there is a fault with the camera. If you could point me in the direction of a solution to this problem I would be very grateful. I did wonder if the AE-L - Af setting in the custom menu should be set - any idea if this might be the cause of the trouble.?

I have recently purchased an istDS and have a Tokina 50-200 K mount lens which I originaly bought for my Pentax KX (which I still have !). Last night I thought I would try out the Tokina on the DS and initially I could get no response from the camera. Quick read of Page 179 of the manual revealed that I had to set 'Use aperture ring' in the Custom Setup. Hoorah ! a little progress - managed a shot with flash after setting Focussing to manual. To cut a long story short _ I have three questions:-
1) Should the Focus Indicator in the viewfinder light up when focus is obtained using manual focussing in this manner.? (Pages 44,121)
2) Page 179 bottom - All Lenses "When depth of field is checked (Preview), AE Metering is switched on. Exposure check is possible." Can anyone explain this in simple terms as nothing seems to happen with the lens I have mentioned when I press the Preview lever.

Can anyone tell me if the built in flash on the istDS meters the exposure received by the subject and shuts down when the subject has received sufficient exposure, or must one always use the guide no. and aperture/distance calculation and manual settings.