Hello,
I hope someone can help. I recently purchased a new Tamron 17-50 f/2.8 because my old one seemed way out of focus when shooting at infinity. I've come to realize that the old lens was actually severely front-focusing. It had, in the past, developed the dreaded loose front element, which I fixed myself. I thought I had maybe not tightened up the front element properly (some may know that the front element can be loosened and rotated in and out slightly to calibrate, or this is what I have read). I tried the front element tightened down at various points along its possible rotation path, but the lens was still severely front-focusing (maximum AF fine adjustment in the K-5 menu was not able to solve the problem completely, but gets it fairly close at f/2.8. It could probably use an adjustment of -11 or -12, if it were possible)
So, I ordered a new lens. The new lens requires -9 AF fine adjustment, or almost the maximum possible of -10! Also, the new lens is less sharp (or less contrasty, I can't really tell) than my old lens when shot wide open using live view AF and self timer on a tripod. Is this two bad lenses or is my K-5 body messed up?
Also of note are the two lenses do not seem to have the exact same optical axis when mounted. Carefully mounting both copies so as not to disturb my set-up, the exact center of the image of my test target is in a slightly different spot in the frame when shot with each lens. This leads me to think my new lens and/or my old one is bad...
But, I also made some observations that lead me to think at least part of the problem is with my K-5 body: images of the target taken with both lenses are rotated about 1.25 degrees counter-clockwise. I was very careful to make sure both the target and camera were dead level before taking photos. Also, the center point of the image migrates slightly to the upper left of the frame as the lenses are zoomed in - this happens on both lenses. Is this normal? These results lead me to think that I have a misaligned image and or phase-detect sensor in my K-5 body. In addition, the images from both lenses appear softer on the left side.
So, do I have bad lenses, a bad body, or a combination of the two, and what do you think I should do? I must return the new lens very soon if I am to get a refund on it. Thanks, in advance, for your help!
~ Jon
P.S. My K-5 was purchased new from an authorized dealer and has just under 5000 clicks on the shutter, and I have taken very careful care of it (not that this precludes it from developing problems)
P.P.S My Tammy 90mm f/2.8 macro requires -5 AF fine adjustment on my K-5 at this point, but I have not tested it further yet.
P.P.P.S. Here are 100% crops of the old (self-repaired) lens and the new Tammy 17-50 that I just ordered:
Last edited by jon.partsch; 10-28-2018 at 08:52 PM.
Reason: Add photo attachment