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07-30-2017, 03:47 AM   #1
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Mid shoot last night. Auto focus not working in viewfinder but is in live view

I was mid way through a shoot last night at a 18 yo birthday party.

Shoot was going great, 50mm f1.8 prime lens beautiful.

Decided to swap to an old film lens I had received earlier that day. Pentax-F zoom 28-80mm.

Nice shots still going perfect. Then swapped back to the 50mm prime, 50 shots later auto focus stopped working.

AF focus motor goes from top to bottom then back again never getting focus.

AF still works in live view mode but not in view finder.

Tried a reset, changed battery, changed lenses 3 times and did a firmware update Still the same. Tried back button focus still the same.

Would appreciate any and all help.

07-30-2017, 04:30 AM   #2
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try cleaning the contacts
07-30-2017, 04:41 AM - 1 Like   #3
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QuoteOriginally posted by sergysergy Quote
try cleaning the contacts
What should I clean them with? I tried a soft cloth earlier. It's still focuses in live view so don't think it is an issue lens side
07-30-2017, 05:57 AM   #4
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maybe in changing lenses you got dust in the mount which has settled on your AF sensor. try giving the camera a going over with a rocket blower

07-30-2017, 05:57 AM   #5
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Could be an issue with the AF sensor, or perhaps dust or an obstruction inside the mirror box.

Adam
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07-30-2017, 06:42 AM   #6
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What camera you use? It seems contrast detection is ok. Thus the af module may have been uncalibrated. Does your camera have focus calibration? Have you tried it? Also, did you try in sun daylight?
07-30-2017, 07:00 AM   #7
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QuoteOriginally posted by RangerMD Quote
What camera you use? It seems contrast detection is ok. Thus the af module may have been uncalibrated. Does your camera have focus calibration? Have you tried it? Also, did you try in sun daylight?
pentax K-70. i dont think it does have focus calibration. yes tried in sunlight and indoors issue persists
07-30-2017, 07:02 AM   #8
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QuoteOriginally posted by pschlute Quote
maybe in changing lenses you got dust in the mount which has settled on your AF sensor. try giving the camera a going over with a rocket blower
I dont have a rocket blower atm unfortunately I lent it to someone

07-30-2017, 07:04 AM   #9
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QuoteOriginally posted by Adam Quote
Could be an issue with the AF sensor, or perhaps dust or an obstruction inside the mirror box.
if it was an issue with the AF sensor wouldnt that affect live view auto focus as well???
07-30-2017, 07:53 AM   #10
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QuoteOriginally posted by Lurch1066 Quote
if it was an issue with the AF sensor wouldnt that affect live view auto focus as well???

Nope. LV autofocus uses contrast detection directly off the camera sensor. Entirely seperate from the AF system used when using the viewfinder
07-30-2017, 08:36 AM   #11
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QuoteOriginally posted by pschlute Quote
Nope. LV autofocus uses contrast detection directly off the camera sensor. Entirely seperate from the AF system used when using the viewfinder
thanks for the info ill give it a try now
07-30-2017, 10:00 AM   #12
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QuoteOriginally posted by Lurch1066 Quote
AF focus motor goes from top to bottom then back again never getting focus.
That means that it could not discern adequate detail to focus on. The usual causes are:
  • Inadequate light for subject
  • Low contrast lighting on low contrast subject
  • Focus point on ambiguous or featureless portion of subject
  • Low contrast lens
  • Centering defect or other optical problems with the lens
  • Atmospheric issues (smoke, dust, etc.)
  • Dust on AF sensor (extremely rare on a new camera)
With the exception of dirty sensor, all of the above would affect manual focus or even human vision. A good rule of thumb might be that if you can't see clearly, neither can your camera.


Steve

(...clean the contacts? I guess it never hurts...)
07-30-2017, 10:37 AM - 1 Like   #13
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QuoteOriginally posted by stevebrot Quote
Dust on AF sensor (extremely rare on a new camera)
He was at a birthday party....maybe a bit of cake !!!!!!!
07-30-2017, 12:05 PM   #14
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QuoteOriginally posted by Lurch1066 Quote
if it was an issue with the AF sensor wouldnt that affect live view auto focus as well???
No, live view uses the image sensor. The viewfinder uses a separate sensor behind the mirror.

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07-30-2017, 01:34 PM   #15
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QuoteOriginally posted by stevebrot Quote
That means that it could not discern adequate detail to focus on. The usual causes are:
  • Inadequate light for subject
  • Low contrast lighting on low contrast subject
  • Focus point on ambiguous or featureless portion of subject
  • Low contrast lens
  • Centering defect or other optical problems with the lens
  • Atmospheric issues (smoke, dust, etc.)
  • Dust on AF sensor (extremely rare on a new camera)
With the exception of dirty sensor, all of the above would affect manual focus or even human vision. A good rule of thumb might be that if you can't see clearly, neither can your camera.


Steve

(...clean the contacts? I guess it never hurts...)
Tried multiple locations with flash on and off still the same not focusing. I could see fine. Ive cleaned the contacts twice still no change but thanks for info and advice
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