Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
11-20-2009, 05:54 PM   #1
Forum Member

Join Date: Nov 2009
Posts: 50
Focus "creep" on 18-50

I (more or less) just got my K-x, mounted the Sigma 18-50 2.8 and, of course, played around with the video mode. What i noticed was that if i manually focus and then zoom in or out, the movement of the zoom ring seems to "take" the focus ring with it to some extent, basically screwing up the shot.

Is this to be expected of lenses below, say, 1000 bucks or do i have a faulty unit on my hand? If the latter, should i just return it to the seller(still have 14 days left for no questions asked return) or is something the lens warranty would cover and i could somehow get fixed?

11-20-2009, 08:48 PM   #2
Veteran Member
Andi Lo's Avatar

Join Date: Jul 2008
Location: Halifax, Nova Scotia
Posts: 2,925
Check first if it's a good copy. If it's not return / exchange it. If it is then send it to sigma for the focus ring repair. Although I've heard that Sigma sometimes think that some things we see as a defect aren't actually a defect and will refuse to fix it... YMMV.

FWIW my DA 10-17 is like this as well when going from 10 to 17, and that lens is no slouch when it comes to build quality.... the tolerance is too tight probably. My other AF zooms doesnt suffer this though.
11-20-2009, 09:03 PM   #3
Site Supporter
Site Supporter
enoeske's Avatar

Join Date: Jul 2009
Location: Surprise, Az
Photos: Gallery
Posts: 2,029
I'm not sure if the zoom is making the focus ring turn (could very well be a faulty lens) or if the problem is much simpler. The focus at 18mm will be different than the focus at 55mm. You cannot zoom in, focus, and then zoom out and have the area previously in focus stay in focus. This lens doesn't work that way. And very few do.
11-20-2009, 09:22 PM   #4
Veteran Member

Join Date: Mar 2009
Location: Perth Australia
Photos: Albums
Posts: 1,514
Yeah this is normal, focus after zooming

11-20-2009, 09:26 PM   #5
Veteran Member
keyser's Avatar

Join Date: Aug 2009
Location: Tsawwassen, BC
Posts: 376
Yeah, there are two types of zoom lenses - Varifocal and perifocal - It sounds like your lens is varifocal and changes focus when the focal length is altered.

  • 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!
focus, k-mount, pentax lens, return, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
K10D shutter will not "snap" but focus/flash work! PlumRT Pentax DSLR Discussion 9 01-13-2011 07:11 AM
Sports "Highside Exit" took 1st Place in DPReview "Missed It by THAT much, Part 1" Challenge MRRiley Post Your Photos! 27 02-21-2010 08:26 PM
What does "auto" mean on older manual focus lenses? jonhock Pentax SLR Lens Discussion 18 12-03-2009 11:32 AM
Intermittently working "Catch-in-focus" while using m42 screwmount lens shuttervox Pentax DSLR Discussion 1 08-06-2009 07:55 PM
"Hunger for a DA*50-135?" or "The DA*50-135 as a bird lens!" or "Iron age birds?" Douglas_of_Sweden Post Your Photos! 4 08-13-2008 06:09 AM

All times are GMT -7. The time now is 11:30 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]