Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-11-2017, 07:14 PM   #1
Veteran Member




Join Date: Sep 2013
Location: Pasadena, CA
Photos: Albums
Posts: 1,125
How is your 16-50 autofocus accuracy in S-AF?

Hi,


I am wondering if anyone else has trouble with their AF accuracy on 16-50, specifically in PDAF. It's not a matter of front or back-focus, it just fails a great deal of time, and almost always when using focus points in the corners. It looks great in CDAF, which makes me think it is not mechanics. Anyone got similar experiences?

01-12-2017, 01:34 AM   #2
Loyal Site Supporter
Loyal Site Supporter
BigMackCam's Avatar

Join Date: Mar 2010
Location: North-East of England
Posts: 15,514
I don't have the 16-50, however... As you're probably aware, only three middle focus points of the K-3 (that's what you're using, yes?) have a focus sensitivity of f/2.8. The rest - including those in the corners - are rated, I think, at f/5.6, so focusing using those points won't be as consistently precise. I suspect that might be what you're experiencing, and you may notice the problem on any fast lens at wider apertures when using anything but the three central focus points.

Last edited by BigMackCam; 01-12-2017 at 01:39 AM.
01-12-2017, 01:56 AM   #3
Veteran Member




Join Date: Sep 2013
Location: Pasadena, CA
Photos: Albums
Posts: 1,125
Original Poster
I thought so too, initially, but often it is off even at f8, and by a lot. It's to a point where landscape shots are unsharp if I use corner focus points. I wonder if this has happened to anyone before.
01-12-2017, 03:40 AM   #4
Loyal Site Supporter
Loyal Site Supporter
BigMackCam's Avatar

Join Date: Mar 2010
Location: North-East of England
Posts: 15,514
QuoteOriginally posted by rrstuff Quote
I thought so too, initially, but often it is off even at f8, and by a lot. It's to a point where landscape shots are unsharp if I use corner focus points. I wonder if this has happened to anyone before.
Hmm... that is a bit odd. Does it happen in good lighting? My Sigma 17-50 sometimes needs a second AF cycle to focus accurately on outer focus points in less-than-stellar light. I've taken to focusing twice out of habit...

01-21-2017, 01:14 AM   #5
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 17,400
I recently converted a working 50-135 that had significant focus issues on SDM to screwdrive. The owner wanted to see if this could improve with Screwdrive- it DID! the change was pretty dramatic. So while it might not help; if you can I suggest trying.
01-21-2017, 07:36 AM   #6
Veteran Member




Join Date: Jul 2010
Location: Lyngby, Copenhagen
Photos: Albums
Posts: 742
I often have trouble autofocusing my 16-50 towards the short end. It'll often front focus 1-2 meter. I've learnt to anticipate it and work around it by doing the zoom-in-focus-zoom-out-again thing.

I've also experienced the phenomenon described by the OP, with all focus points. I attribute that to an old worn SDM drive.

Regards,
--Anders.
01-21-2017, 08:01 AM   #7
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 17,400
It is important to note that the lens I mentioned above was not sluggish nor squeaking. I compared it to my own 50-135 and the difference on SDM with it giving up on tough focusing situations was clearly and easily seen. Once switched to screw drive this behavior vanished. This was not really something I had ever seen before. Since then others have mentioned similar findings.
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!
accuracy, autofocus accuracy, k-mount, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
16-50 gross AF inaccuracy in PDAF - only in some AF points? rrstuff Pentax SLR Lens Discussion 9 11-19-2016 11:29 AM
How torquey is your K-1's mirror? 6BQ5 Pentax K-1 7 09-18-2016 10:39 AM
Select AF point(s) vs. single (spot) point ... any difference in accuracy? jpzk Pentax K-3 35 05-06-2016 05:31 AM
K-5 autofocus accuracy varies by AF point Designosophy Pentax K-5 22 01-19-2012 08:32 AM
K5 and DA*16-50 ... How's the AF?? germar Pentax K-5 6 12-20-2010 11:16 AM



All times are GMT -7. The time now is 07:57 PM. | 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