Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
12-28-2011, 07:24 PM   #16
Veteran Member




Join Date: Jan 2010
Location: Durham, nc
Photos: Albums
Posts: 895
Original Poster
Sorry, mm not cm. Mistyped that one. Every other lens I own is spot on.

Target was the word "Dark". The Grey King was pulled out by about 1cm, and it is what is in focus.


and the chart:


It is obviously front-focusing by a large degree.

I can reproduce these same results over and over again, it's rare to get an in-focus image. If I use my 50mm f1.7 at f1.7, that autofocus is perfect. I get an in-focus image more often than not even with the narrower DOF.

Charles.

12-28-2011, 08:05 PM   #17
Veteran Member




Join Date: Mar 2007
Location: Boston, PRofMA
Photos: Albums
Posts: 3,053
Charles: doubt you're imagining things. I went through 3 copies of the Tamron 28-75 before giving up. Massive BF/FF problems wide open and one had really bad ghosting. Yes, they can be total crap. I'd only buy it new and from a place that has a good exchange policy. Unfortunately, I didn't have time to keep going (needed it for an event and ended up making do w/ a Sigma 17-70)...
12-29-2011, 08:21 AM   #18
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
The book test is meaningless as the target was not unambiguous. The focus test chart does seem to show a slight - couple of mm - apparent FF. I take it that is with no adjustments? So have you performed the tests I described to see if the behavior changes based on the starting point? And where's the shot from the 50 taken under the same lighting with the same adjustment?
12-29-2011, 09:50 AM   #19
Veteran Member




Join Date: Jan 2010
Location: Durham, nc
Photos: Albums
Posts: 895
Original Poster
The book test is not unambiguous. I made 10 shots with the tamron, 2 turned out with good focus and 2 with acceptable focus. The rest were junk. I made 10 shots with the 50mm @f1.7, 10 shots turned out with good focus. Just for shits and giggles, I made 10 shots with the 50mm at f2.8, and 10 shots turned out razor sharp. I didn't post the others because I didn't think it worth the effort, hosting space, or loading time for this page, but if you really want to see, I'll do that.

But it boils down to this: I get a much, much higher rate of in-focus images with every other lens I own. EVERY. OTHER. LENS. Even the faster lens. That tells me it's not my technique, and not my camera. Which leaves only one thing left in the equation: The lens.

Charles.

12-31-2011, 09:41 AM - 1 Like   #20
Pentaxian
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
Photos: Gallery
Posts: 10,686
Of course the nook test is ambiguous - assuming that's a crop, you have no eay of controlling which book the camera actually chose to focus on, because the AF sensors are so large.

Your logic of comparing number of good shots may seem sound, but it still files in the face of physics, so that's why I'm saying, you really need to test more thoroughly, and chances are very good that you'll eventually discover that in fact your lens is *not* somehow violating the laws of physics. The "placebo effect" can be just as strong with lenses as with medicine.
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!
autofocus, copy, distance, f2.8, focus, k-mount, pentax lens, slr lens, tamron, tokina
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Contest Your best shot with a Tamron lens rfortson Mini-Challenges, Games, and Photo Stories 57 05-23-2011 03:15 PM
Tokina 28-70 f2.8 vs. Tamron 28-75 f2.8 HoBykoYan Pentax SLR Lens Discussion 2 06-16-2010 11:45 AM
Sigma vs Tamron vs Tokina letgo12345 Pentax SLR Lens Discussion 23 04-08-2010 01:37 PM
One Shot with Tokina AT-X 80-200/2.8 MF tux08902 Post Your Photos! 5 12-10-2008 12:28 PM
Anyone want to take a shot at PP this one? Or give me some ideas? lapeen Post Your Photos! 13 10-16-2007 01:39 PM



All times are GMT -7. The time now is 04:27 PM. | 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