AF fine tuning - D7100 & 18-200mm

<p>A couple of years ago, I had a lens that was front focusing (18-200mm), and I had to do an AF Fine Tune on it (all the way to -15 on my D7100). I hadn’t been too happy with the sharpness of my lens lately, and this morning I noticed that it was back focusing, and had to move the setting almost all the way back to the original position. Has anyone else experienced this?</p>

<p>mm Challengewith zoomlenses is : Mostly the compensation for the long end of the lens is different from the compensation at the short end ...<br>

So if its ok at 200mm, then its mostly off at 18mm and vice versa ...<br>

Even if it is ok at the average ( 108mm.) then it can be front focussing on the long end and back focussing at the short end ...</p>

<p>@ C.P.M. van het Kaar – Thanks for your insight. That makes sense, but in this case, the fine tuning was made both times to correct for focus at the shorter end. I just find it odd that the focus point is shifting. I will probably have to send it back to Nikon for repair (or replace it if the repair cost is too high). Just wondering if others had experienced this instability.</p>

I haven't had any real problems with focusing on this lens but having used this lens extensively, I have found it is only

sharp at f10 At all other apertures softness is very pronounced and can often look very much like poor focusing.