Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-12-2015, 06:58 PM   #1
Site Supporter




Join Date: May 2010
Posts: 5,251
DA* 50-135mm focus hunts

It appears my 50-135mm focus hunts at 135mm. It is quite interesting as I can zoom out a little (roughly to 125mm) and I will get a lock near instantly.. even if I purposely defocus and let the camera find its focus altogether.. but as soon as I move it to 135mm, it just goes back and forth slightly. The other interesting thing is it doesn't seem to rack the focus, going from one side to the polar opposite completely. No, my lens @ 135mm just slightly focuses towards me, through correct focus, then out slightly, again through correct focus.. very quickly.. and never finding where it needs to be. infinite hunting.

And, if I manually correct it with the quick shift.. the lens does nothing (as it should), the camera beeps, and I have lock. haha thanks AF for letting me do your job.

Also, after going through a period of hunting.. if I move the focal length again to say 125mm and keep trying to let the camera find focus, it does... near instantly.

What is going on?? I've tried it at f/2.8, f/4, and f/8 ISO 400 and ISO 100.. bright light.. dim light.. it doesn't matter. It is like it KNOWS where correct focus is (since it doesn't move through the whole focus range, sticking to just on each side of proper focus).. but it refuses to give it to me.

09-12-2015, 07:03 PM   #2
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 40,942
QuoteOriginally posted by mee Quote
It appears my 50-135mm focus hunts at 135mm. It is quite interesting as I can zoom out a little (roughly to 125mm) and I will get a lock near instantly.. even if I purposely defocus and let the camera find its focus altogether.. but as soon as I move it to 135mm, it just goes back and forth slightly. The other interesting thing is it doesn't seem to rack the focus, going from one side to the polar opposite completely. No, my lens @ 135mm just slightly focuses towards me, through correct focus, then out slightly, again through correct focus.. very quickly.. and never finding where it needs to be. infinite hunting.

And, if I manually correct it with the quick shift.. the lens does nothing (as it should), the camera beeps, and I have lock. haha thanks AF for letting me do your job.

Also, after going through a period of hunting.. if I move the focal length again to say 125mm and keep trying to let the camera find focus, it does... near instantly.

What is going on?? I've tried it at f/2.8, f/4, and f/8 ISO 400 and ISO 100.. bright light.. dim light.. it doesn't matter. It is like it KNOWS where correct focus is (since it doesn't move through the whole focus range, sticking to just on each side of proper focus).. but it refuses to give it to me.
What camera? Also, it might need a very slight AF adjustment at the long end.

Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)



PentaxForums.com's high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

09-12-2015, 07:36 PM   #3
mee
Site Supporter




Join Date: May 2010
Posts: 5,251
Original Poster
K-5 II

No, I don't think it is a micro focus issue... I've tried it at -10 to +10 and various values in between. the behavior is the same at 135mm.

It gets to correct focus, over shoots SLIGHTLY then corrects by going through correct focus just to the other edge of it and then proceeds to hunt back and forth between near edges. So it seems to know where to go, it just never seals the deal by committing to correct focus.

Last edited by mee; 09-12-2015 at 07:44 PM.
09-12-2015, 07:56 PM   #4
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 40,942
QuoteOriginally posted by mee Quote
K-5 II

No, I don't think it is a micro focus issue... I've tried it at -10 to +10 and various values in between. the behavior is the same at 135mm.

It gets to correct focus, over shoots SLIGHTLY then corrects by going through correct focus just to the other edge of it and then proceeds to hunt back and forth between near edges. So it seems to know where to go, it just never seals the deal by committing to correct focus.
I've had something like this happen with very wide lenses, but not telephotos. Strange!


Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)



PentaxForums.com's high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

09-12-2015, 08:03 PM   #5
mee
Site Supporter




Join Date: May 2010
Posts: 5,251
Original Poster
QuoteOriginally posted by Adam Quote
I've had something like this happen with very wide lenses, but not telephotos. Strange!
Strange indeed! What was the resolution for the very wide lenses exhibiting a similar behavior?
09-12-2015, 08:23 PM   #6
Pentaxian
K57XR's Avatar

Join Date: Feb 2011
Location: Colorado, USA
Posts: 810
QuoteOriginally posted by mee Quote
It appears my 50-135mm focus hunts at 135mm. It is quite interesting as I can zoom out a little (roughly to 125mm) and I will get a lock near instantly.. even if I purposely defocus and let the camera find its focus altogether.. but as soon as I move it to 135mm, it just goes back and forth slightly. The other interesting thing is it doesn't seem to rack the focus, going from one side to the polar opposite completely. No, my lens @ 135mm just slightly focuses towards me, through correct focus, then out slightly, again through correct focus.. very quickly.. and never finding where it needs to be. infinite hunting.

And, if I manually correct it with the quick shift.. the lens does nothing (as it should), the camera beeps, and I have lock. haha thanks AF for letting me do your job.

Also, after going through a period of hunting.. if I move the focal length again to say 125mm and keep trying to let the camera find focus, it does... near instantly.

What is going on?? I've tried it at f/2.8, f/4, and f/8 ISO 400 and ISO 100.. bright light.. dim light.. it doesn't matter. It is like it KNOWS where correct focus is (since it doesn't move through the whole focus range, sticking to just on each side of proper focus).. but it refuses to give it to me.
My 50-135 (Screw-Drive) does exactly the same thing. I tried on three bodies (K5, K-01 and a K-r) - the thing zips back and forth at 135, but locks almost instantaneously around 100-120mm. Is yours running screw-drive or SDM? My SWAG on it is related to SDM hack, but why on the long end only?
09-12-2015, 08:44 PM   #7
mee
Site Supporter




Join Date: May 2010
Posts: 5,251
Original Poster
QuoteOriginally posted by K57XR Quote
My 50-135 (Screw-Drive) does exactly the same thing. I tried on three bodies (K5, K-01 and a K-r) - the thing zips back and forth at 135, but locks almost instantaneously around 100-120mm. Is yours running screw-drive or SDM? My SWAG on it is related to SDM hack, but why on the long end only?
Interesting! Thanks for sharing..

I'm using SDM.. I was actually contemplating, this evening, switching it to screwdrive to see if it was ill behaved after.. looks like I won't need to bother now.

hmmmmmmmmmmmmmmmmmm..........
09-12-2015, 09:11 PM   #8
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 40,942
QuoteOriginally posted by mee Quote
Strange indeed! What was the resolution for the very wide lenses exhibiting a similar behavior?
It was a while ago, but it must have been with the K-7 or K-5 as a small AF adjustment seemed to solve the issue.


Adam
PentaxForums.com Webmaster (Site Usage Guide | Site Help | My Photography)



PentaxForums.com's high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

09-15-2015, 03:54 PM   #9
mee
Site Supporter




Join Date: May 2010
Posts: 5,251
Original Poster
QuoteOriginally posted by Adam Quote
It was a while ago, but it must have been with the K-7 or K-5 as a small AF adjustment seemed to solve the issue.
Oh that is a different issue then..
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!
135mm, camera, focus, iso, lens, lock, move, pentax help, photography, troubleshooting
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Focus hunts with DA 1.4X AW AF Rear Teleconverter and other Qs DavidDwight Pentax SLR Lens Discussion 6 04-21-2015 09:03 PM
New-to-me DA* 50-135mm is squeaking with SDM focus Nick Siebers Pentax SLR Lens Discussion 10 08-12-2014 04:32 PM
Help - Infinity focus problem with DA* 50-135mm 2.8 chickentender Pentax SLR Lens Discussion 9 08-06-2009 10:20 PM
DA* 50-135mm Focus ring GLXLR Pentax SLR Lens Discussion 15 06-29-2009 08:10 AM
Focus ring question (DA* 50~135mm, DA*16~50mm) bingsean Pentax SLR Lens Discussion 6 03-20-2009 11:20 AM



All times are GMT -7. The time now is 07:30 PM. | See also: NikonForums.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