I've been using a 200 f/4 Q.C mounted on a TC-16A as a poor man's telephoto for birds, but ended up with poorly focused shots on my last outing. I posted about this a few days ago and was advised that there seemed to be a front-focusing issue (http://nikonites.com/telephoto/36738-advice-needed-sharp-bird-shots.html#axzz4CKuipBCq). I checked the focus points and they seemed to be on the subject, so I figured that the setup could have a front focus issue (not noticeable for close-in subjects, but apparent for subjects 25 ft or beyond).
Yesterday, I looked into AF Fine Tune, and got some interesting findings. My subject was a cereal box with a ruler at 45 degrees adjacent to it, about 20 feet away. At this distance, however, AF seemed to be accurate as far as I could tell. Just for grins, I dialed in an adjustment of -20, and didn't see much of a change in the photo. Then I dialed in +20, and again, nothing seemed to have changed. This surprised me a little. Wondering if there's an explanation of this, and more importantly, if there's a preferred way to diagnose a front focus / back focus issue and correct it with AF Fine Tune. Thanks!
Yesterday, I looked into AF Fine Tune, and got some interesting findings. My subject was a cereal box with a ruler at 45 degrees adjacent to it, about 20 feet away. At this distance, however, AF seemed to be accurate as far as I could tell. Just for grins, I dialed in an adjustment of -20, and didn't see much of a change in the photo. Then I dialed in +20, and again, nothing seemed to have changed. This surprised me a little. Wondering if there's an explanation of this, and more importantly, if there's a preferred way to diagnose a front focus / back focus issue and correct it with AF Fine Tune. Thanks!