Answer B Daniel - well spotted.

I actually worked it out late last night. The fact that it was onlty doing it with the one lens was really doing my head in until it struck me that I hold the camera differently with the longer lenses on. Somehow the switch ion the grip had got knocked on. Mystery solved.

Thanks Gents

No problems here hand holding the 150-500 either.

I agree with Kris about telephotos and crops too.

I think it is suffering withdrawal symptoms as it has not been out for a while.

All the indications are that the "exposure half presses switch" is intermittently shorting so the camera will suddenly try to or actually focus. If I pop the flash up it will give focus assist. I have nothing unusual set and CAF is off.

The only thing that blows this diagnosis is that it only does it with one lens - my DFA 100.

At the moment it is having a spell without it's batteries to see if that helps.

Anyone got any ideas?

Have a look at page 81 item 12 of your distructions. This may help.

Mike - George is quite right to be concerned. Compressor oil is not cheap and should not be wasted on lenses.

I was wondering how long it would take for someone to spot that Yves.

Thanks Techno. If it's the same as the K20, the light (orange on mine) is on when the card is being written to or read from.

Pentax are a little ambiguous about alkalines. They say toward the beginning of the manual that they are suitable, then later they say that you may get reduced functionality with them. I'd be very surprised is they stopped the camera switching on at all though.

Putting a battery in the wrong way round may toast the battery and the camera would not work, but it is unlikely to damage the camera.

Sorry if this is a silly question but are you putting the batteries in the right way round? Might be worth checking.

Something else to check. On my K20 with the switch off and the battery in, when I insert an SD card, the card read light flickers a couple of times. Could another Kx owner confirm that they do this too. If so that would be another thing to check.

Just my two pennorth -

It seems a bit sad that we get to a point where we only consider our rights and not other peoples' wishes.

D'Oh!!

I knew the answer but still got it wrong because I didn't read the options properly.

RTFQ