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08-13-2011, 04:57 PM   #1
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Join Date: Jan 2010
Location: Las Vegas
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K-7 18-55mm focus problem.

Hi,
I have been having this problem for a long time with the K7 and the 18-55 kit lens.
Once in a while it would not want to auto focus. Just couldn't "lock" the focus. It would run the focus in then out and give up.
I figured it must be too dark of a shot or something.
Today it was happening almost all the time.
I was at Zion taking some landscape shots and with the lens at 18mm it just wouldn't auto focus at distant mountains or closer trees. It would try to run the focus out past the stop and give up. If I zoomed in a bit it could focus.
Non of the other lenses I have (55-300, 35, 10-17) have ever had a problem.
tried a search but no answers.
Lens issue?
I tried seating the lens again, taking off IR and polarizing filters etc. The auto focus mechanism is working fine, just won't lock focus.
Any ideas?
Thanks,
Dave

08-14-2011, 04:01 AM   #2
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Join Date: May 2010
Location: Borlänge, Sweden
Posts: 373
Got the same problem at infinity focus. Crap lens.

Get a 16-45 f4.
08-14-2011, 09:36 AM   #3
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hmmm... try to clean your lens's contacts and also the rear element of the lens. =)
08-14-2011, 01:38 PM   #4
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Its trying to focus past infinity at 18mm. Shouldn't have anything to do with the contacts, I would think.

08-14-2011, 09:24 PM   #5
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Join Date: Jan 2010
Location: Las Vegas
Posts: 5
Original Poster
So i figured out the problem.
There is a bit of "slack" in the lens.
If I pull out on the end of the lens it will move the end of the lens out just a tiny bit.
When the lens is pulled out it will not lock focus.
If I push the lens in it will focus.
Just that tiny bit (couple thousandths of an inch) of movement will not let the lens get into focal range.
I took the lens completely apart to see if I could correct the problem, it is all plastic and no way to tighten it up.
There is two shims that adjust the lens element distance to the sensor. I removed those shims and re-assembled the lens. Problem gone.
I am trying to think if this will affect the focus of my shots. In removing those shims it adjusted the whole lens about 20 thousandths of an inch closer to the sensor, not just one lens element.
Will the camera AF adjust for this?
I can't decide.
What is the standard focus test I should preform to check the lens and adjust for?
Thanks,
Dave
08-15-2011, 06:59 AM   #6
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Join Date: Aug 2008
Location: Michigan, USA
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Posts: 7,485
Just take some pictures with the thing and see what happens. The best 'tests' are those that give you real world results. You can stand around and take photos of charts and such until your feet take root in the ground. It will mean very little if the lens is still performing poorly when you want to take a real photo with it. I would think in Las Vegas you would have plenty to try it out with.

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