Several years ago I picked up a used AF VR Nikkor 80-400 4.5 5.6D. Got enough of a deal, that based on an influential review, and in the face of some expert advice against, I bought it. Was supposed to be a problem solver, small enough with reasonable reach. From the beginning, it wasn't, because I'm all in on sharpness. Sometimes I would achieve very acceptable results (probably Luck & perfect conditions), others, just a bit fuzzy. Been on my To Do list - fix or unload. A bit overcast this afternoon, but had time so put it on the D750 and walked outside to wring it out a bit. The only bird I saw was one of my resident Flycatchers #1 - low end acceptable. Then a beat up butterfly #2-4 - I had half again as many outtakes as usual, but considering the overcast, low end, nearly o.k. . Finally, a little bee wrestling, #5. My question - I have not had to adjust AF on a Nikon lens, seems like a bit of a PITA. Based on lens tuning you have experienced, Do you think the process might improve sharpness enough to make the lens a keeper?

Looking at you images, quixdraw, I don’t think the problem is front or back focus. If you go to the areas that seem to be be in sharpest focus ( where the area in front and in back of it begin to blur more) that area is plainly not sharp, as TriX said above. There are several potential answers and a simple test to tell which one it is. Possible answers:

1 The lens is a gobbling turkey;
2 You are seeking to enlarge too tiny a portion of the frame
3 the combination of long focal length, slower shutter speed and enlargement make handholding a problem;
4 The lens was used wide open and is not sharp at that aperture.

There is a simple test for a calm day. Tape a test target (a magazine page with several sized fonts for example) to a shaded side window of your car or house.. Blue painters tape should not leave any residue. Tripod mount your camera and lens at a suitable distance. Stop down two stops from maximum aperture. Open live view and use a magnified view to manually focus and note the letter and word you are focusing on. Use a remote trigger. If the image is not acceptably sharp at the point of focus, then you have a gobbler

Irwin

I would not use the images you have posted for me to make any judgement on your lens performance with respect to 'sharpness'/'possible AF tuning'. They are too small, we have no idea where you 'actually' focused, whether they have been cropped or the speed/aperture/ISO you used.

I have the 80-400 and found I had to AF fine tune significantly 'only' for when used with a 1.4TX at 400mm because I needed to shoot specific subjects at max aperture. But that is likely only specific to my own lens.

With respect to perceived sharpness I wonder how you 'measure' this? For myself, I expect my lenses to produce stunning sharp animal hair when the image is un-cropped, sized at 1920 px wide and viewed on my monitor.

If I were you I would find a static 'hairy subject', put your lens on tripod with timed release and firstly confirm that it can produce 'sharp' results that you are happy with using your own measurement method.

If you find that the lens can produce consistent acceptable results then for anything not acceptable there has to be a reason, or a combination of reasons.

The next thing to do if it does produce acceptable sharpness is to check that the plane of acceptable sharpness is where you expect it to be.

Several years ago I picked up a used AF VR Nikkor 80-400 4.5 5.6D. Got enough of a deal, that based on an influential review, and in the face of some expert advice against, I bought it. Was supposed to be a problem solver, small enough with reasonable reach. From the beginning, it wasn't, because I'm all in on sharpness. Sometimes I would achieve very acceptable results (probably Luck & perfect conditions), others, just a bit fuzzy. Been on my To Do list - fix or unload. A bit overcast this afternoon, but had time so put it on the D750 and walked outside to wring it out a bit. The only bird I saw was one of my resident Flycatchers #1 - low end acceptable. Then a beat up butterfly #2-4 - I had half again as many outtakes as usual, but considering the overcast, low end, nearly o.k. . Finally, a little bee wrestling, #5. My question - I have not had to adjust AF on a Nikon lens, seems like a bit of a PITA. Based on lens tuning you have experienced, Do you think the process might improve sharpness enough to make the lens a keeper?