600 mm f/4G ED sharpness issue

[Vagabondvern1]

Hey all, I'm having some sharpness issues with my Nikon 600 mm f/4G ED, I thought I would reach out to people way smarter than I am for some help. Let me explain, I have it mounted to my Nikon Z9, the images are completely unusable, and it's hard to describe what the issue is. they seem noisy, blurry and hazy. Now this lens was tack sharp and performed beautifully on my D850, but since upgrading to the Z9 is when my troubles started. I can mount my 400mm 4.5 S to the Z9 and the images are tack sharp as well as my F-mount 70-200mm, it just seem as if the 600 f/4 and the Z9 are not communicating. I had the 600 Z9 combo calibrated, and everything was fine there. Any ideas on what the issue might be? I have attached 2 untouched pictures of the 600mm and the 400mm. sideways cow is 600mm strait on cow is 400mm, same distance, same settings same rest (bean bag window shot)

 

[StefanSC]

Find a straight brick wall.
Put Z9 and 600mm f4G on a tripod at a reasonable distance.
Focus manually for maximum sharpness and take picture. Disable VR.
Rotate lens 180 degrees on it's tripod collar (you will be shooting with your camera upside down).

Compare pictures to see if they are similar. If not, you might have a decentering in lens or some sort of misalignment in your FTZ adapter.

 

[Vagabondvern1]

Find a straight brick wall.
Put Z9 and 600mm f4G on a tripod at a reasonable distance.
Focus manually for maximum sharpness and take picture. Disable VR.
Rotate lens 180 degrees on it's tripod collar (you will be shooting with your camera upside down).

Compare pictures to see if they are similar. If not, you might have a decentering in lens or some sort of misalignment in your FTZ adapter.

Thanks Stefan, I will try this first thing tomorrow morning.

 

[Marcepan]

Maybe what wrong with FTZ adapter?

 

[Len Shepherd]

You seem to have eliminated the camera body as it works as it should with another lens.

Are these the only photos taken with the 600mm?

If yes were you using animal detection - in which case I wold expect better unless perhaps if using pinpoint AF.

If you were not using AI subject detection there is little detail in the white or black part of the face of the subject - a hard task for most AF systems - including your D850 - for the AF to accurately detect the subject. When this happens I find AF can hunt for about half a second - and then gives up - often out of focus.

Testing with another subject should provide more information.
A brick wall I consider "only OK" as the Z9 without AI only focuses only on vertical lines in a wall. You will get enough information as to whether the image is sharp as distinct from critically sharp.

 

[Rassie]

In the 600mm image, the focus is on the top of the cow's back. The hair there is in better focus than the face itself. The focus was not on the eyes of the cow but behind the head.
Try again and make sure you focus exactly on the eyes. If the camera has difficulty with that with autofocus, then focus manually using the focus peaking highlights in the Z9. Once the focus is where it should be we can evaluate lens sharpness again.

Please also report camera and lens settings (aperture, shutter speed, ISO, etc.). Was VR on or off?

 

[DRwyoming]

Good advice above but FWIW, when I have concerns over a lens and potential softness issues I shoot a fixed target and test out best focus achieved manually as well as what the AF system can achieve and with a long and heavy lens I make sure I do that from a solid support like a good tripod at a high shutter speed in decent light.

IOW, rule out lens issues with some careful testing and if that all checks out then think about all the other potential factors like focus area mode, shutter speed in real life situations, whether you have sufficient support or good long lens techniques to go along with such a long and heavy lens and the like.

I agree with @Rassie's post above that the photos you posted appear to be back focused and the hairs on the cow's back are sharper than the eyes which could just be an AF subject detect issue as black eyes against black fur can confuse automated focus modes and subject detection. So it might just be choosing a different AF approach for that kind of subject but if you're worried about the lens itself, break it down and rule out lens issues with some careful testing on static subjects.

 

[EricBowles]

Like DR, when I have a question about lens performance, I go back and do simple testing with a good AF target. Something like the cow in the photos above can present AF challenges. It's not a flat surface, the eye may not present as the easiest target, and there are lots of alternative targets. I've had similar challenges with owl photography where there are long feathers in front of the eyes on the bridge of the nose, so I have to be very precise with focus technique.

I'd set up a proper flat target and do some more testing. Part of that is to confirm the lens is operating properly and is capable of sharp and accurate focus.

For difficult AF targets, I often fall back to Dynamic, Single, or even Pinpoint AF. I have Pinpoint included in my AF Area options, and it only shows up when I change to AF-S. I also have a Fn button programmed to zoom to 100%. This gives me the ability to check focus if needed before the shot, or check focus on playback. It's also very useful when birding to let me look at a subject closely for identification or to check focus when I am shooting through obstructing twigs or grasses.