I do not use Nikon equipment but there are reasons why a photo is sharp or nor regardless of the brand used. You do not give out two important pieces of information, one camera used and shutter speed. a low shutter speed will not give a clean photo on a tripod unless you use a cable remote or timer to trigger the shutter. If your camera does not have a F8 focal point, most FF cameras do but some crop sensor cameras do not, the converter will change an F5.6 aperture to an F8 and your camera may not be able to focus properly. Last F8 on a long telephoto does not give a large DOF and your subject may not be in the proper focal plane. What is the MP count of your camera if it is not high enough and you do a heavy crop your photo will not be sharp. Last tip for people that photograph these birds as I do, I photograph from a 14 ft long Kayak wide enough to give stability when using a Pentax K5ii and a Sigma 120-400 mm lense. or look for a NWR that has a auto rout that you can drive through to photograph wildlife.

I just received a Nikon 200-500 and a Nikon 1.4 teleconverter and tested them today on a extremely long distance shot of a Great Blue Heron. Using a tripod I took one series of photos without the teleconverter and another set with it. Camera settings on both were f/8 and both were taken at approximately the same time, under the same lighting using a tripod. The only pp done was a small amount of color correction and a heavy 1:1 crop. Then I enlarged the photo that was taken without the teleconverter to 140% in photoshop (a 1.4 software enlargement) to make the subjects same size in both photos.

Can anyone guess which was done using the teleconverter?

Vision can make a mundane image spectacular. Even though Ansel Adams was a major proponent of straight out of the camera images and unmanipulated contact prints made from large negatives, and devised an entire exposure control system to enable this, all of his work seems to have been manipulated.

The other things that happens is that what you envision today may be totally different if you interpret the image 5 yrs from now. In fact this image below has had many iterations though the years, to the point that he took his only negative of this scene and re-processed it to further enhance the contrast.

Like the work of many SOOC advocates - the first image below is an excellent exposure but not a memorable image, But it is a good exposure since it has all the elements necessary to "create" an image based on his vision. To my eye, given the tools currently available (camera/lens, software, techniques), most SOOC images leave lots of "money on the table" as far as impact is concerned. Put another way, I have yet to see a single SOOC image that could not be improved upon with skillful application of post processing. Even images taken in a studio where there is 100% control over lighting, can be improved.