Golden Rule Loc: Washington State

I am going to do the f/stop exercise and see how each shot looks.

autofocus Loc: North Central Connecticut

it's really two separate issues, addressing DOF with a smaller aperture will not solve a lens that won't focus correctly

ABJanes Loc: Jersey Boy now Virginia

Here is what the DoF Calculator reports for a D750

85MM f/8 focused at 15' has acceptable focus 1'11.3" in front and 2'7.5" in the rear.
85MM f/8 focused at 20' has acceptable focus 3'3.9" in front and 4'11.9" in the rear.

85MM f/11 focused at 15' has acceptable focus 2'7.3" in front and 4'0.1" in the rear.
85MM f/11 focused at 20' has acceptable focus 4'4.8" in front and 7'10.4" in the rear.

Do you own an iPhone? If so, the calculator is on the iTunes Website (App for $1.99 as I recall)

There are alternative DoF Calculators for Android phones.

I think moving up through the f/stops will help you find a look that you will be happy with. Others can share on how to's for PP sharpening techniques. Olympus had a recent article on their website about photographing pets, you may want to search it out. I will see if I can find it.

ABJanes Loc: Jersey Boy now Virginia

Yup....and f/8 & f/11 should prove that out.

ABJanes Loc: Jersey Boy now Virginia

Here is the Olympus article.......http://www.getolympus.com/us/en/learn_center/epic-dog-shots?utm_medium=CustomContent&utm_source=Adlucent&utm_campaign=OMDLow&utm_content=Pet&gclid=Cj0KCQjwtOLVBRCZARIsADPLtJ1hIClPUR8xkHvpbKdhHh8jAS9iCL2hlA-Nt-JO3qv2ikppUEaWYvoaApqUEALw_wcB&kwid=297877821556x52012368717x1045106324

TriX Loc: Raleigh, NC

The OP has repeatedly stated that he wants to isolate the dog, especially the head, from the background. He should be able to do that somewhere between f2.0 and f3.5-f4, but if he chooses the larger aperture, his AF will need to be spot on, and if it isn’t (and he doesn’t want to manually focus, which can be tough with a moving animal), then making sure the lens’ AF is not front or back focusing and caling as necessary is the first step. Simply moving the fstop up to increase the DOF just hides any AF problem. If your AF is spot on, you can isolate the subject with a wide aperture, and that is why I carefully calibrate all my lenses. For example, a 200mm on a FF at f3.5 and 35 feet to subject yields just under 2 feet or 1.5 feet at f2.8 - plenty to both insure sharp focus on the entire face and good subject/background isolation IF the focus point is correct AND the AF is correct. Very similar results if you choose 100mm, same apertures and 15-20 feet to subject, or f2.8 at 85mm and 15 feet yields 1.6 feet DOF - more than enough. On the other hand, f2 or below is cutting it a bit close.

autofocus Loc: North Central Connecticut

if you, or the camera lens combo misses tack sharp focus, f/8 or f/11 will not solve it. So, in that case, you can have deep DOF, yet still have a soft eye, or target area. But let me go back to some of the basics I eluded to earlier. All lenses have sweet spots both in apertures, and in focal lengths for zooms. Some lenses just won't yield sharp critical focus at certain F/stops no matter what you do...you just have to live with it, fix it, or get a different lens. Edges of many lenses are typically softer than the center. So, if your subject happens to be near the edge, they will appear softer. Higher ISO's will degradate clarity, and it will be very noticeable when zooming in BUT, most people aren't viewing photos or enlargements at 100% magnification. The op has indicated he wants tack sharp clarity while getting soft decoupled backgrounds. He will not get that look very well shooting with an 85 at f/8 or f/11...remember, he wants to shoot at around f/2, and still have sharp eye focus, and with that lens there's no reason why he can't have that (with a properly adjusted lens and a proper shooting style,) so why are we telling him to shoot at f/8? That simply does not address his problem.

autofocus Loc: North Central Connecticut

looks like we're playing off the same song sheet :)

TriX Loc: Raleigh, NC

Indeed we are.

autofocus Loc: North Central Connecticut

problems can often be easily addressed, mindsets, well, that's another thing :)

cjc2 Loc: Hellertown PA

FYI, my copy of this lens was tack sharp out of the box. You may have an issue with yours. I use it all the time wide open and the focus speed and accuracy is exceptional but the DOF can be very thin. You might want to consider returning it for another sample or trying it on another camera. Best of luck.

SteveR Loc: Michigan

I went to Arlington Camera with my daughter a week ago Saturday to buy a D7500 for her. I took a 35-80 lens with me. I have used the same Nikon salesman for years, who is also a photographer. He took a photo of my daughter with my lens and the 7500 focusing on her eyes and determined that it had focused behind her eyes. He fine tuned the the camera for the lens on the spot and it was much sharper (as shown on a large Apple monitor). My suggestion....take a photo focusing on eyes and then determine where the focus point is. Is it spot on, behind, or in front of the eyes? Then fine tune accordingly.

SteveR Loc: Michigan

I went to Arlington Camera with my daughter a week ago Saturday to buy a D7500 for her. I took a 35-80 lens with me. I have used the same Nikon salesman for years, who is also a photographer. He took a photo of my daughter with my lens and the 7500 focusing on her eyes and determined that it had focused behind her eyes. He fine tuned the the camera for the lens on the spot and it was much sharper (as shown on a large Apple monitor). My suggestion....take a photo focusing on eyes and then determine where the focus point is. Is it spot on, behind, or in front of the eyes? Then fine tune accordingly.

ABJanes Loc: Jersey Boy now Virginia

I re-read all of the posts and I am here to apologize. Going to fast and I misunderstood the requirement. What I have observed is that many do not use some helpful tools to be more accurate in how DoF varies relative to the lens, f/stop and distance. The DoF Calculator for the iPhone is one such tool. Bracketing the f/stops would be a quick check to see the problem as the DoF increases, f/8-f/11 should be very forgiving and if it too is out of focus the problem is identified "proof perfect". Many also do not compose, move the focal point, auto focus and then take the shot when shooting with fast lenses wide open. When the DoF is extremely shallow, moving the camera can change the plane.

(Download)

JPL

I think the OP should carefully read the posts so far and check possible issues with his gear.
It is a nonsense to use a f/1.4 lens at f/8 to get useable pictures. This lens will deliver sharp pictures even at f/1.4. But the OP is trying to get sharp pics at f/2.0 That is easy.

I have not seen any response to instructions about checking the camera firmware and upgrade to the latest version. The D750 is known to have misaligned focus points. That was corrected in firmware upgrade. It is also known to need fine tuning with this particular lens to get sharp results. And then there is the possibility of low contrast and larger focus points then indicated in the viewfinder disturbing the focus system. Some or all of those are the most likely causes of the problem the OP is facing. The problem will continue as long as those basic and obvious solutions are ignored.