Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
11-01-2010, 02:18 PM   #1
New Member

Join Date: Oct 2010
Posts: 9
Focus problem on FA50mm

Well I have just got my first dSLR, a K10d, and on it went my old lenses, a FA-50mm and a Sigma 28-200.
While playing with them, I noticed that the AF on the 28-200 is pretty fast and accurate, but I didn't get any AF on the FA-50mm - just a small movement, some noise and it freezes.

After a short check this is what I found out:
1 - Without changing any settings on the body, the 28-200 Autofocuses without a hitch, however there is a problem with FA-50mm. So I assume the problem is not related to body .

2 - On manual focus mode the FA-50mm does recognize when it is focused (I see the green hexagon lights up and a red square blinking). So the body focus recognition is okay.

3 - When I try to focus with FA-50mm there is a short noise, less than a second but the focus doesn't budge. It is the same behavior whether the lens is at infinity and I point it an object 1 meter away, or whether the lens is at 0.8 meter focus and I point it at the same object.

4 - I tried to clean contacts, using soft eraser, it didn't help. the Mechanics on the back seem fine (i.e. no damage visible).

5 - It seems to me that when I manual focus the FA-50mm the friction is much higher compared to the 28-200.

6 - the focus ring center-line on the FA-50 is not aligned with the lens center-line, i.e. The space between the focus ring and the ring below it is not-uniform, varying from 0.5mm to roughly 2mm.
see attached images.

So I think that the problem is the increased friction / misalignment, however my experience in dSLR is nil, and the last time i used my film SLR was something like 10 years ago...
So I would be glad to hear your ideas / thoughts - maybe it is a common problem with a simple solution... and whether I can fix it in home or do I need to get it to a service shop.


Attached Images
View Picture EXIF
PENTAX K10D  Photo 
View Picture EXIF
PENTAX K10D  Photo 
11-01-2010, 03:22 PM   #2
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 47,234
It sounds like this lens was clocked right there on the focus ring, resulting in internal damage. Might have to send it in if you want the AF to work.

Adam Webmaster (Site Usage Guide | Site Help | My Photography) server and development costs are user-supported. You can help cover these 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:

11-08-2010, 07:07 AM   #3
New Member

Join Date: Oct 2010
Posts: 9
Original Poster
I have sent the lens to a service shop, they identified the problem with a malfunctioning (broken?) worm-gear of the auto-focus.
The fee they want for the fix is ~170USD, is it reasonable?

11-08-2010, 07:20 AM   #4
Veteran Member
Reportage's Avatar

Join Date: Feb 2009
Photos: Gallery
Posts: 739
QuoteOriginally posted by koraldon Quote
I have sent the lens to a service shop, they identified the problem with a malfunctioning (broken?) worm-gear of the auto-focus.
The fee they want for the fix is ~170USD, is it reasonable?

Up to you. A used one here in good condition is about US$300.


  • 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, body, fa-50mm, focus, friction, i.e, k-mount, lens, meter, object, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
K10D and focus problem cherno Pentax DSLR Discussion 10 10-10-2010 09:09 PM
Focus problem, but only sometimes? StarDust Pentax SLR Lens Discussion 9 10-08-2010 04:36 PM
problem with focus? nowicjusz Pentax DSLR Discussion 2 03-30-2010 09:57 AM
K7 Focus problem sudupoosa Pentax DSLR Discussion 12 03-10-2010 11:53 AM

All times are GMT -7. The time now is 12:45 AM. | See also:, 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?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]