Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-27-2010, 10:12 AM   #1
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
Different focus correction for each end of a zoom?

So after learning about the moire interference technique and getting repeatable accurate focus correction values, I started to do all my lenses. One lens has a correction of +20um at 18mm, but +140um at 50mm. This is repeatable from different focusing distances and whatnot. Is this common at all or a defect?


The Moire interference technique for those inclined:
AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D
Using Moire' Interference Patterns to Test DSLR Auto Focus

Most accurate, can do indoors without worrying about tungsten, easier to line up 100% perpendicular yet less affected by it compared to a focus chart.

10-28-2010, 01:24 AM   #2
Veteran Member




Join Date: Jan 2009
Location: Budapest
Posts: 821
I've heard of this with some lenses. I'd consider this a defect, on the other hand if it's a design or manufacturing flaw affecting all (or large series of) copies of the lens then you can't do much other than sell it and get a different type / brand.

What you could try is to set it at the middle of the zoom range (~34-35mm) and then check how much it's off on the wide and tele end, I mean can you easily notice focus being off or is it so subtle that only pixel-peeping reveals some small softness.
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!
correction, focus, focus correction, interference, k-mount, pentax lens, slr lens, technique
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K-X front / back focus correction, lens tested ea77 Pentax DSLR Discussion 3 12-07-2009 06:56 PM
Experience with focus correction on K-m jerrymouse Pentax DSLR Discussion 3 09-10-2009 11:19 AM
Powerful High-end color correction software wildman Digital Processing, Software, and Printing 7 05-22-2009 08:10 AM
K20D Focus correction question sabarrett Pentax DSLR Discussion 4 08-22-2008 12:38 PM
Lightweight wide-end zoom? Kguru Pentax SLR Lens Discussion 5 02-12-2008 06:26 AM



All times are GMT -7. The time now is 11:02 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