So, I decided to check the calibration on my Nikon 35-70 today and found something weird.
I first tested it on the Df with the Live View feature. Tested all apertures from 2.8 through 8, at 35, 50, 70mm - all good.
I then switched over and did another series - same aperture progression.
Camera and lens were on a tripod.
When I reviewed the images, this time, f/2.8 and 4 looked good, but when it got to f/5.6 it was slightly blurry, out of focus. So I repeated the test multiple times and I keep getting the same result. This only happens when the lens is at 70mm. All other focal lengths look as they should.
I tried AF fine tuning, but nothing helped. I know, such a problem to have a lens that is sharper at f/2.8 than f/5.6, but I didn't expect this.
I put the lens on the D700. No problem. AF is spot on at every focal length and every aperture range tested.
OK...weird, I think...so I put the lens on the D500. Exact same issues with the AF @ 70mm and f/5.6.
My initial conclusion is that there must be some issue with the newer cameras AF systems. The D700 having the oldest AF system out of the bunch.
I'm not sure what I'm going to do with the lens as I got it primarily for use on the Df. I used to have an older 28-85/3.5-4.5 that worked great on the Df, so if I cannot resolve this issue with the 35-70, I'm thinking of going back to that lens or maybe looking into the 28-105 or similar for walkabout purposes.
Thanks in advance for any help or suggestions you might have.
My plan is:
1) I'm trying to understand the issue
2) Figure out if there is a fix for it
