Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-18-2011, 06:11 AM   #1
Site Supporter
Site Supporter
1marek's Avatar

Join Date: Aug 2009
Location: Medjimurje, Croatia
Photos: Albums
Posts: 40
Prime lenses AF adjustment

I have a question regarding AF accuracy of prime lenses when shooting objects that are closer vs objects that are further away. I don't know what to think of a lens which doesn't need any AF adjustment when shooting at MFD, but it needs a helluva lot when shooting objects that are more distant - +10 with objects at approximately 3 metres away (close to infinity) and like +15 at infinity. Could this be a matter of misalignment of elements?

10-18-2011, 06:34 AM   #2
Site Supporter
Site Supporter
jpzk's Avatar

Join Date: Jan 2009
Location: Québec
Photos: Gallery | Albums
Posts: 8,251
QuoteOriginally posted by 1marek Quote
I have a question regarding AF accuracy of prime lenses when shooting objects that are closer vs objects that are further away. I don't know what to think of a lens which doesn't need any AF adjustment when shooting at MFD, but it needs a helluva lot when shooting objects that are more distant - +10 with objects at approximately 3 metres away (close to infinity) and like +15 at infinity. Could this be a matter of misalignment of elements?
I am glad someone else (you) posted about this and explained the situation better than I did here:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/162500-da-15mm...us-issues.html

but you will find some very interesting answers / solutions in that thread of mine.

I have a DA 15mm Ltd lens which I find rather tough to fine tune (AF) on the K7, but for some reason it is perfectly in focus with the K5, with no AF adjustment. Go figure!

I am now testing this same lens with my old K20D and it looks that it won't need as much adjusting as with the K7.

I hope you will find a way to fine tune your lens too.

Cheers.

JP
10-18-2011, 09:30 AM   #3
Site Supporter
Site Supporter
1marek's Avatar

Join Date: Aug 2009
Location: Medjimurje, Croatia
Photos: Albums
Posts: 40
Original Poster
Thanks for the tip, I completely missed your topic, cr**py PF search engine....
After reading advices they gave you, first thing that comes to my mind is to maybe dial in +10 in order for the lens to work better at infinity but this would be just a lousy compromise... 'cause my logic tells me that you would take more pics at or near infinity with a 15mm lens than with a longer lens. Correct me if I'm wrong.

When I first tested the lens+body combination with focus test charts, I put in +3 and thought that would do the job... seems logical since chart testing is done at distance of approximately 2 feet... So, bang on at MFD, +3 at 2 feet and +10 at infinity.

Has anyone else had this problem and then send it to Pentax for calibration? I'm wondering if such a body/lens can be tweaked to AF properly on both ends of the distance scale.
I haven't done any hard core scientific focus tests on tripod (except with the focus charts) but it is bluntly clear that AF is not working as it should, and since there is this progression of AF ailment, it seems to me that body may be the culprit. What do you guys think? Plese feel free to chime in.

Oh, I almost forgot, the gibbled combination is K-5 + FA31
10-18-2011, 09:32 AM   #4
Site Supporter
Site Supporter
1marek's Avatar

Join Date: Aug 2009
Location: Medjimurje, Croatia
Photos: Albums
Posts: 40
Original Poster
I still need to do some tests with the k-r to confirm the ''body's the culprit'' theory but to me it seems a good theory.
Anyway, I would like to resolve this because I use the lens almost exclusively on a K-5

10-19-2011, 11:48 PM   #5
Veteran Member
hoanpham's Avatar

Join Date: Nov 2009
Location: Strand
Photos: Gallery | Albums
Posts: 1,366
Some lenses need to fine tune AF, some not. Same lens on different bodies may and may not. Mine took some time to adjust, and remember to note down lens-body combination and adjustment value. It's easy to erase them all.
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!
adjustment, af, infinity, k-mount, lenses, objects, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K-5 AF fine adjustment - does it work for non Pentax lenses? Christine Tham Pentax K-5 & K-5 II 30 12-28-2011 01:35 PM
Just did AF Fine Adjustment - all my lenses are off?! HenrikDK Pentax K-5 & K-5 II 30 07-27-2011 06:55 PM
Hyperfocal adjustment on current vs manual lenses kbrede Pentax SLR Lens Discussion 41 03-22-2011 10:52 AM
adjustment of infinity focus on Kiron lenses Lowell Goudge Pentax SLR Lens Discussion 24 04-12-2010 05:19 PM
[k-7] AF adjustment for M42 lenses Nass Pentax DSLR Discussion 3 02-12-2010 07:44 AM



All times are GMT -7. The time now is 01:31 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