Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-12-2017, 11:19 AM   #1
New Member




Join Date: Aug 2017
Posts: 12
autofocus inaccuracy, green spots on the mirror?

Hi all,

I am wondering if you have thoughts on this. My k-3 started having inconsistent autofocus about a year ago. I cleaned contacts , af sensor with no improvement.

Yesterday I looked at the mirror under microscope and found green residue (spots?) around the edge of the af mirror, according to this graph, number 3:
How Phase Detection Autofocus Works

Any ideas what's going on? Separation of some layers?

08-12-2017, 11:27 AM   #2
New Member




Join Date: Aug 2017
Posts: 12
Original Poster
Green spots visible here

Sorry about the bad picture, it's difficult to capture the spots. They are behind the mirror, and the green residue is both in spots scattered around and on the edge of the smaller mirror, behind the front one.
Attached Images
View Picture EXIF
QCAM-AA  Photo 
08-12-2017, 11:42 AM   #3
New Member




Join Date: Aug 2017
Posts: 12
Original Poster
Here's a better image of the sub mirror spots.
Attached Images
View Picture EXIF
QCAM-AA  Photo 
08-12-2017, 12:56 PM - 1 Like   #4
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,489
Welcome to the Pentax Forums!

Yes, those could affect AF performance, though probably be reducing precision and ability to detect the point of best focus. Misalignment of either the secondary or main mirror may also screw things up. If it were me, I have would have the camera professionally cleaned and mirror alignment adjusted, assuming, of course, that the spots are a foreign substance on the surface.


Steve

08-12-2017, 01:16 PM   #5
New Member




Join Date: Aug 2017
Posts: 12
Original Poster
QuoteOriginally posted by stevebrot Quote
Welcome to the Pentax Forums!

Yes, those could affect AF performance, though probably be reducing precision and ability to detect the point of best focus. Misalignment of either the secondary or main mirror may also screw things up. If it were me, I have would have the camera professionally cleaned and mirror alignment adjusted, assuming, of course, that the spots are a foreign substance on the surface.


Steve
Hi,

I don't think they are a foreign substance. The spots appear around the edges too, it looks like some glue or coating separation. Precision wants 300usd for a repair so I am not sure if it is worth it. The af inaccuracy is consistent with the spots, I.e. Some work better than others.
08-12-2017, 06:47 PM - 1 Like   #6
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,489
QuoteOriginally posted by randomstuff Quote
Hi,

I don't think they are a foreign substance. The spots appear around the edges too, it looks like some glue or coating separation. Precision wants 300usd for a repair so I am not sure if it is worth it. The af inaccuracy is consistent with the spots, I.e. Some work better than others.
Looking more closely at your photo, it appears that the mirror has been exposed to moisture (cleaning solution?) at some point. Repair vs. replace...that is the old conundrum. If your K-3 is in otherwise excellent condition with low shutter count, repair might be a good option. If you can find a used body in similar condition with no known problems for $300, that would also work. More typical of market prices, KEH currently has an EX+ K-3 body with a 180 day warranty for $572.


Steve
08-12-2017, 08:26 PM   #7
New Member




Join Date: Aug 2017
Posts: 12
Original Poster
QuoteOriginally posted by stevebrot Quote
Looking more closely at your photo, it appears that the mirror has been exposed to moisture (cleaning solution?) at some point. Repair vs. replace...that is the old conundrum. If your K-3 is in otherwise excellent condition with low shutter count, repair might be a good option. If you can find a used body in similar condition with no known problems for $300, that would also work. More typical of market prices, KEH currently has an EX+ K-3 body with a 180 day warranty for $572.


Steve
I paid $599 for a new one 2 years ago, albeit from Canada and an unauthorized dealer. I wonder what happened with the prices since then. I tried cleaning the spots, but I am not sure if matters are improved, since it will take some time. It frankly looks like some adhesive that got flapped off from the mirror - edges are green and there are splash spots in the middle. I never did a wet cleaning on it. I might bring it over to a store and get it done if AF doesn't improve.

Thanks for the suggestions.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
af, autofocus, camera, mirror, pentax help, photography, troubleshooting
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Landscape Green, Green and more Green AussieTrev Post Your Photos! 4 02-19-2017 06:29 AM
16-50 gross AF inaccuracy in PDAF - only in some AF points? rrstuff Pentax SLR Lens Discussion 9 11-19-2016 11:29 AM
Pentax 645N apperture mismatch and metering inaccuracy sniper29a Pentax Medium Format 12 04-10-2014 03:42 PM
AF inaccuracy? "Student" Pentax K-3 14 02-24-2014 12:00 PM
AF inaccuracy.. Fabian Pentax SLR Lens Discussion 7 12-11-2010 01:12 AM



All times are GMT -7. The time now is 10:22 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top