SteveR Loc: Michigan

Jerry....we all know how much you've sunk into camera equipment.....I have an idea you couldn't be happy with a Brownie!!

BigDaddy Loc: Pittsburgh, PA

After 6 Years And 720,000 Attempts, Photographer Finally Takes Perfect Shot Of Kingfisher
http://www.boredpanda.com/perfect-kingfisher-dive-photo-wildlife-photography-alan-mcfadyen/

I remember years ago looking at spectacular hummingbird photos by a guy that did mostly hummingbird photos. When asked about how he got such great photo's he said only a few he considered great, out of like 70,000 photos he considered 2, maybe 3 as great. His idea of "great" was much, much, much more exclusive than mine.

I often read in the hog people complaining about folks taking too many pics, they should learn to shoot one or two good ones... like they did in film days. Plenty of awesome photographers would disagree.

I have incredible trouble getting sharp as a tack photo's. I blame it on my lenses, but I occasionally get one that is sharp enough, so perhaps it's just really difficult with some setups.

Meives Loc: FORT LAUDERDALE

It is important to post with "store original" when asking a question like this. The download is much better, and the camera settings may tell a story.

Djedi

OK, enlarged, I now see what you mean. It almost looks as if this was cropped from from a larger photo and the original was shot at ISO2400 and had noise reduction applied.
I owned the Nikkor 300mm f4 (Non-stabilized) and it was an extremely sharp lens, with fabulous micro-contrast. That is what I believe is missing in this photo and could happen if shot at too high an ISO. It could also happen if the camera was shaken when the photo was taken, or if slightly out of focus.
But, after looking at the specs on your photo, I see it was shot at 800 which should present NO problem for the D500, and you should not be losing sharpness to noise reduction.
Soooo....
Looking very closely, I do not see the typical "shaken" look with faint, off axis secondary or tertiary images, so I would rule that out as well.
That leaves us only one possibility- focus.
It looks to me like there is nothing directly behind the owl (fabulous specimen, BTW) that IS actually in focus, but, the feather just in front and below the owl, and some of the brambles seem to be in better focus than our main subject (though not totally clear either).
Soooo...
I would vote for a front-focus issue, possibly combined with poor light (no sunlight on the owl).
I might even check if the same issue happens with other lenses (a camera mount mis-alignment issue) or maybe even a poorly aligned lens element.
Resolution:
My first, quick solution would be to rent another quality 300mm lens and see if the issue persists. If the shots are sharp, replace your lens. If they are still OOF, send the lens and D500 to nikon.
w

Charles 46277 Loc: Fulton County, KY

"Sharp as a tack" refers to mental capacity, I think, and for that a tack is pretty sharp. A surgeon's mind might be sharp as a scalpel, though. A wasp's sharpness is in the other end, in my experience. Application to photographs is metaphorical.

"How sharper than a serpent's tooth it is. To have a thankless child.—Away, away!" (King Lear, Act 1, sc. 4, p.13). Perhaps the thankless child can be improved in post processing. Or not.

Dorothy Parker said the first things she did when she got up in the morning were to brush her teeth and sharpen her tongue.

https://www.britannica.com/topic/Algonquin-Round-Table
https://www.goodreads.com/author/quotes/24956.Dorothy_Parker

She also said, "It was all my own fault--I should never have put all my eggs in one bastard."

Charles 46277 Loc: Fulton County, KY

Yes--getting closer or using longer lens improves picture quality by avoiding cropping--larger sensor could also be mentioned (or larger film), and so could adding light if possible (higher ISO, shutter, aperture). These all permit bigger enlargements as well. The maxim is that greater magnification is better done when shooting the picture than when making the print. Of course, longer lenses have their own problems--cost, sharpness, and difficulty to use (weight, shake, expensive filters, slower speeds).