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08-20-2020, 11:47 AM   #1
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Focus hunting on kit lens - DA-L F4-5.6 18-50 mm DC WR RE

I have a K-S2 that's about 18 months old, with the 18-50mm kit lens. It's not a bad little lens for snapshots and family outing photos, and I especially liked the quick and quiet focus - until now....
It has just starting, 'acting up', hunting in and out of focus, and often settling slightly out of focus.

Is the lens now garbage? Anything I can do/try to fix it?

Frank

---------- Post added 08-20-20 at 11:48 AM ----------

I should add that it's not the camera - it works fine with other lenses.

08-20-2020, 12:55 PM   #2
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Hmm- that surely is unusual for a lens to develop sudden mis-focus issues! Since it doesn't happen with other lenses, perhaps something is wrong with one or more of the contacts. A good cleaning might be the cure. I have the same kit with my little K-S2, which is a marvelously compact combination, and has worked fine so far.

Have you tried using center-only spot focus? I generally shoot with this setting, and use the shutter button half-press to secure focus on an edge or clearly defined part of the subject, then hold the focus with the half-press while moving the camera to the desired composition to complete the half-press for the shot.
08-20-2020, 01:09 PM   #3
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I mainly use back button focus and center-only, but I've tried most other combinations. I'll try cleaning the contacts - rubbing alcohol on a swab?
08-20-2020, 01:41 PM   #4
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I would ask around and find another body to test on - even if this is the only lens acting up. Try a nice bright daylight shot or two also.

08-20-2020, 02:30 PM   #5
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QuoteOriginally posted by Frank29 Quote
I mainly use back button focus and center-only, but I've tried most other combinations. I'll try cleaning the contacts - rubbing alcohol on a swab?
yep, just a little so the alcohol won't run inside the camera.
08-20-2020, 03:29 PM - 1 Like   #6
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QuoteOriginally posted by Frank29 Quote
Is the lens now garbage? Anything I can do/try to fix it?
The other thing I would suggest is to use the sensor cleaning function to raise the mirror and use a good rocket blower inside the mirror box to clean any dust off the AF sensor (bottom of the mirror box). I know you said that the camera does AF ok with other lenses but the 18-50 is a slow lens and that may mean it is more likely to have problems with a dusty AF sensor.
08-23-2020, 10:06 AM   #7
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As it turns out, the camera seems to be the issue. It is doing the 'focus hunting' with my other lenses, but it is much more subtle with the screw drive lenses.
Does the focus work fundamentally different in live view than with the viewfinder? What kind of things should I test to narrow down the problem, and what possible fixes are there?

08-23-2020, 11:43 AM   #8
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QuoteOriginally posted by Frank29 Quote
As it turns out, the camera seems to be the issue. It is doing the 'focus hunting' with my other lenses, but it is much more subtle with the screw drive lenses.
Does the focus work fundamentally different in live view than with the viewfinder? What kind of things should I test to narrow down the problem, and what possible fixes are there?
Yes. Live view is contrast detection based. Use a nice contrast friendly target with good lighting.
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