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Pentax-F 70-210 focus problem

Posted 30/03/2014 - 13:49 Link
I recently purchased a second hand Pentax-F 70-210 which I have been delighted with until it developed a problem focussing.

It works properly if I am focussing on a subject nearby. However if the subject is further than ~ 20feet the focus never locks i.e. the focus confirmation light in the viewfinder keeps blinking. Using manual focus does not work either.

Now on another forum someone stated they were able to fix this by loosening 3 screws and turning something or other. However I really have no idea what they were getting at!

Has anyone here experienced this problem and been able to fix it?

I'd be very grateful of any advice.

Posted 31/03/2014 - 00:01 Link
Are you sure you are focussing on something the autofocus can lock on to? that is something with pattern or texture. I cant see how it wont focus manually.
“We must avoid however, snapping away, shooting quickly and without thought, overloading ourselves with unnecessary images that clutter our memory and diminish the clarity of the whole.” - Henri Cartier-Bresson -
Posted 31/03/2014 - 01:00 Link
Hi Ken

I suppose the best way to describe this is that it won't focus on infinity.
The lens locks on focus fine as long as what I am focussing on isn't too far away.

I recently used it to take images of "The Rat Pack" at The Playhouse,Edinburgh. Took several hundred photos in a few hours with (what I thought!) great results. Next time I went out I was at Stirling Castle and discovered this focussing problem! I'm now wondering if the extensive use at the gig sort of broke it!

From the lens review section on another forum I got this quote:
"EDIT TO THE EDIT: Ok, with the great posts of some members here, I was easily able to correct the infinity focus issue by simply moving the focus to infinity on the scale, unscrewing the 3 screws around the barrel of the lens, moving the focus on the scale slightly to the right, then screwing the screws back in. Problem solved, now focuses to infinity. I probably doesn't focus as close as it use to, but that doesn't matter."

I just can't see the 3 screws referred to.

Upside is I can still use it in a studio setting as subjects are close enough.

Puzzling though.....

Posted 31/03/2014 - 11:39 Link
Hi Ken

I had a Tamron 80-210 ad2 lens that I part dismantled to get rid of some fungus. When I reassembled it , it wouldn't focus on infinity. The front element screwed into the barrel and I had not recorded how many turns I had used to unscrew it.

I removed the three screws in the barrel that secured it, then I had to loosen a notched ring at the front of the element with cocktail sticks. I then adjusted the element by screwing it in or out until it focused on infinity. Finally put the screws screws back in and tighten everything up including the notched ring.

I am not familiar with the Pentax-F 70-210 so may don't have these screws but I would check if it has a notched ring that has become loose and allowed the front element to move.


Posted 31/03/2014 - 12:33 Link
I just can't see the 3 screws referred to.

Normally they live underneath the rubber focus ring

It's been a long time since I had the F70-210, but the images of the FA80-320 may prove helpful:

Look at the last image particularly - there's a tiny clamp for focus adjustment (but you need to remove the three screws under the rubber focus ring to get the front cover off to get to it).

It can happen if you've perhaps rotated the front ring too far - i.e. giving more rotation than the tiny clamp can resist. Can happen if you've had a filter on very tight

(For gallery, tips and links)
Posted 31/03/2014 - 13:04 Link
Hi Ken

I found this link of someone with the same problem and how it was fixed link.

I googled 'pentax f 70-210 lens dismantling' and there is a fair bit of info available.


Posted 31/03/2014 - 13:09 Link
Hi Ken

Also this link link


Posted 31/03/2014 - 21:50 Link
Good news! Have got the lens working again and it thankfully wasn't too difficult

However I would like to thanks MattMatic and screwdriver222 for your your research. Have to admit that screwdrivers comment re "googling" made me smile! How many times have I suggested that? Funny how I didn't think this time. Suppose I have faith in the forum!

Anyway: surrounding the front piece of glass there is a ring with 4 slots in it. See pic of one of them below
Comment Image

I rotated this ring clockwise about a turn and now the lens was focussing properly again.

Happy days

and thanks again

Edited by SamH: 31/03/2014 - 21:50

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