Focussing problem

Help....

I am having a problem with my 16 - 50 on automatic focussing. If I set up a shot the autofocus will not lock onto the subject. If I move the lens away from the subject and then back again it seems to lock on. The camera is set on centre focus, AV and the problem is across the zoom range.

Am I missing something obvious or should i quickly get the guarantee out..

Dave

What focus mode are you on?
If it's on contentious it might thinks the focus is close enough and therefore doesn't focus but that's speculation only.

I think you're finding that the AF doesn't think it needs to do anything to improve the focus and you don't trust it. I bully the AF by focus off subject, compose, press AF button (I don't use the half press) and that makes the AF reassess the validity of its focus.

I have had similar issues. As long as your aware of it, you can do as Mike explains.

Regards

My 16-50 is behaving in a similar manner. I suspect it is the early stage of a autofocus failure. If I turn the focus ring from one end to the other gently, it feels gritty. If I exercise it from one end to the other a few times it will work properly for a while.

I would guess that there is some debris stopping it turning one way and by turning around ant trying to focus you are driving the motor in the other direction, releasing the debris.

It does seem strange

The autofocus does not confirm a focus and will not allow the shutter button to go down and take the shot.

I think the autofocus times out if it has not locked on within a certain time.

Does your focus ring feel gritty?

Oggy The focus ring is fibe.

Stefan I am not sure what you mean by contentiousfocus

The problem occured when I was out doing a few landscapes in bright , slightly hazy weather. When I used the 50 - 135 at the same location it snapped into focus straight away.

I have just tried it in the garden and it seems to be working fine.

Dave

At a very wide angle? Possibly the AF could find nothing contrasty to lock onto?

I've had similar experience with both the 17-70 and the 50-135 and I think mikew is right it's the lack of contrast. Normally I use center point, AF-S and if I move the red square around it usually finds something to lock onto

Thanks guys. I have come to the conclusion that as Barry says it was the lack of contrast that caused the problem as the lens is working in the more normal grey light of Bradford!!!

Phew.....

Dave

continuous
But like others say it should give a focus conformation then.

Happy days

A good news update

After spending months of frustration with the 16-50 only autofocussing when it felt like it, I contacted SRS who sent the lens onto Pentax for checking under their TWO year guarantee. ( only 10 weeks of it left!)

Pentax have replaced the autofocus motor at no charge under the guarantee THANKS PENTAX

THANKS TO SRS for the 2 year guarantee and for honouring it with the second owner.

Now for some sunlight and I can go and play

Happy Dave

A very fine result indeed