Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
04-16-2010, 02:28 AM   #1
Forum Member

Join Date: Apr 2010
Photos: Gallery
Posts: 79
how do i check a lens for front/back focusing and general sharpness?

i am going to buy my tamron 17-50, and i have heard it is important to check and make sure that your copy is a good one. how do i check for the front and back focusing, and general sharpness?

04-16-2010, 03:21 AM   #2
Moderator Emeritus

Join Date: May 2007
Location: Edmonton Alberta, Canada
Photos: Gallery | Albums
Posts: 10,648
General sharpness is fairly easy, Just take some controlled test shots in decent light. If you have a tripod, then set up a still life subject and test the lens at a few different focal lengths and different apertures. If n tripod just put the camera on a solid surface. Use the 2 second mirror lock up.
Then do some of the same (without the timer and SR on) hand held and check the pictures.

Then to check BF/FF, download the focus chart here and follow the instructions exactly. This will tell you what you need to know.
04-16-2010, 05:24 AM   #3
Senior Member
Naim Khan's Avatar

Join Date: Mar 2010
Location: Wakefield, West Yorkshire
Posts: 177
You could try this - it helped me.
Cheers and happy shooting.
04-16-2010, 09:23 AM   #4
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
QuoteOriginally posted by Peter Zack Quote
Then to check BF/FF, download the focus chart here and follow the instructions exactly. This will tell you what you need to know.
Except that in the cases where it does show a problem, it won't really tell you if the problem is with the lens or with the camera without doing further tests (with other lenses of the same focal length and aperture, and with other cameras using the same lens). In general, I believe camera problems are probably far more common, but they tend to go unnoticed when all you have are slow zooms where the DOF is more than big enough to mask any slight focus discrepancy.

On the other hand, the word "problem" is relative term. It's probably normal for all cameras to be off by a millimeter or two, and probably has been since the first AF systems 30-some-odd years ago. But the nature of digital is that everyone's a pixel peeper now, plus it costs nothing to perform the tests, and we can see the results instantly, so everyone's a measurebator too. Discrepancies of a millimeter or two that never would have been noticed ten years ago are now easier to spot. That doesn't mean they actually matter any more than they did before, though.


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

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Front-back focusing issue Mystic Pentax DSLR Discussion 10 08-26-2009 08:15 PM
What Does Front and Back Focusing Mean? GregK8 Troubleshooting and Beginner Help 5 02-28-2009 11:47 AM
Back or front focusing problem jon pafford Pentax SLR Lens Discussion 1 11-15-2008 11:28 AM
Front/Back or random Focusing ckanthon Pentax DSLR Discussion 0 06-21-2008 01:07 AM
Front/Back Focusing Problem? leex0187 Pentax DSLR Discussion 10 07-12-2007 05:34 PM

All times are GMT -7. The time now is 08:19 PM. | 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]