Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-04-2016, 09:17 AM   #1
New Member




Join Date: May 2016
Posts: 5
Focusing issue (weird)

Hi all,
i'm new in the forum and i hope this is the correct section to post this question.

I have a K5 with a Sigma 17-50 2.8, i experienced a weird focusing issue:

If I set the lens at 2.8, no problem at all. I half press the shutter button and the camera autofocus works properly, after that I shoot the picture. Perfect focus. OK

Now, I set the lens at e.g. F8 or F11, and make same procedure: half press -> auto focus -> shoot. Result: back focus!

Another test: Setting the lens 2.8, half press -> focusing OK -> while holding half press the shutter button, i close the lens at e.g. F11 and shoot. Focus perfect! OK

I same way, sounds like the camera tries to compensate some type of focus shift: she knows that the lens is closed at e.g. F11, so recalculates focusing in different manner ... i don't know.

There is some type of focusing shift compensation in firmware? There is a way to disable it? Debug mode or so...

Thank you in advance

05-04-2016, 09:38 AM   #2
Site Supporter
Site Supporter




Join Date: Mar 2008
Location: Prince George, BC
Photos: Gallery | Albums
Posts: 2,809
The K-5 has a problem autofocusing with tungsten lighting at low light levels. Could be what you are seeing.
05-04-2016, 09:51 AM   #3
Senior Member




Join Date: Mar 2013
Location: So-central, MI / Central, IN
Posts: 174
Please give some further description regarding the lighting / environmental conditions. Also try to replicate the problem in bright sunny daylight and if you are indoors with dim incandescent lighting, perhaps try to replicate with using flash.

Is this happening with the camera set to a single point AF sensor (e.g. center), or do you have it on matrix? Also what were you using as a subject, and what was the subject to camera distance?
05-04-2016, 04:37 PM   #4
Veteran Member




Join Date: Aug 2010
Location: Adelaide
Posts: 470
QuoteOriginally posted by DaveK10 Quote
Hi all,
i'm new in the forum and i hope this is the correct section to post this question.

I have a K5 with a Sigma 17-50 2.8, i experienced a weird focusing issue:

If I set the lens at 2.8, no problem at all. I half press the shutter button and the camera autofocus works properly, after that I shoot the picture. Perfect focus. OK

Now, I set the lens at e.g. F8 or F11, and make same procedure: half press -> auto focus -> shoot. Result: back focus!

Another test: Setting the lens 2.8, half press -> focusing OK -> while holding half press the shutter button, i close the lens at e.g. F11 and shoot. Focus perfect! OK

I same way, sounds like the camera tries to compensate some type of focus shift: she knows that the lens is closed at e.g. F11, so recalculates focusing in different manner ... i don't know.

There is some type of focusing shift compensation in firmware? There is a way to disable it? Debug mode or so...

Thank you in advance

I had this exact issue with a Sigma 24-60/2.8 I bought last year, so I returned it.


Also note that some Sigma HSM lenses don't play nice with LiveView CDAF.

05-05-2016, 01:41 AM   #5
New Member




Join Date: May 2016
Posts: 5
Original Poster
Thanks for your reply!

I have done many test in many lighting conditions,set to a single (central) point AF sensor.
Focusing in Live wiev works perfect.





QuoteOriginally posted by krazykat Quote
I had this exact issue with a Sigma 24-60/2.8 I bought last year, so I returned it.


Also note that some Sigma HSM lenses don't play nice with LiveView CDAF.

Now you have another copy of the Sigma 24-60/2.8 that works well?
I mean: the issue is with the single copy or with ALL Sigma 24-60/2.8?
05-05-2016, 03:29 AM   #6
Veteran Member




Join Date: Aug 2010
Location: Adelaide
Posts: 470
QuoteOriginally posted by DaveK10 Quote
Now you have another copy of the Sigma 24-60/2.8 that works well?
I mean: the issue is with the single copy or with ALL Sigma 24-60/2.8?
No, the first copy I got was the worst lens I have ever had the misfortune of attaching to my camera. So decentered it could hardly focus. The second was the one that had the issue. After that I got sick of playing roulette, plus I got a good dose of attitude from the tech I was dealing with, so I cut my losses. Others have been very happy with their copies of the lens though.
05-06-2016, 12:46 AM   #7
New Member




Join Date: May 2016
Posts: 5
Original Poster
Made another test.
Checked K5 - K10 with Sigma 17-50 2.8 and Pentax 17-50 F4.

K10 and K5 with Sigma: same issue. It seems to be a lens (Sigma) problem.... BUT:
check K10 and K5 with Pentax 16-45: same issue. !!!!
Less annoying, maybe negligible, (or maybe not) but still present.

Soon i'll make more test with a friend.




If anybody wants to try, this is the procedure:

1) Focusing an object with central point, lens Wide Open (e.g. f2.8)
Shoot

2) Re-Focusing same object with central point, (best focusing first a far target, and re-focusing the subject, to be sure the AF works), with lens less Open (e.g. f8)
Shoot

3) Re-focusing again our object (best focusing first a far target, and re-focusing the subject, to be sure the AF works), with lens Wide Open (e.g. f2.8) BUT, without shooting, holding half press shoot button (so WITHOUT refocusing), closing the lens at f8
Shoot

In my experience the results are

1) less Depth of Field / Focus OK
2) more Depth of Field BUT Back Focus
3) more Depth of Field BUT Back Focus (like 2, obviously) but Focus OK

Anybody want's to try?

---------- Post added 05-06-16 at 12:50 AM ----------

QuoteOriginally posted by DaveK10 Quote

1) less Depth of Field / Focus OK
2) more Depth of Field BUT Back Focus
3) more Depth of Field BUT Back Focus (like 2, obviously) but Focus OK

Anybody want's to try?
Sorry, little mistake:

1) less Depth of Field / Focus OK
2) more Depth of Field BUT Back Focus
3) more Depth of Field (like 2, obviously) but Focus OK
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!
depth, e.g, field, focus, k-mount, k10, k5, lens, pentax lens, sigma, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Weird AWB issue just popped up mrbdm99 Pentax K-3 7 05-13-2015 06:40 PM
Weird K5 LCD issue sadatoni Pentax K-5 16 07-22-2014 09:35 PM
weird image issue hcky11kev Pentax K-3 24 06-22-2014 10:46 AM
Weird issue after new focusing screen atekant Pentax K-5 8 06-26-2012 08:58 AM



All times are GMT -7. The time now is 01:43 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