Focus issues in a Nikon 24-70 f/2.8 lens

Question

I have a Nikon 24-70mm f/2.8 (without VR) and the pictures taken with it are not sharp and crisp as I think they should be. I use it with a Nikon D7200 that works perfectly with a Nikon 70-200mm f/2.8 VRII and a Nikon 18-140mm f/3.5-5.6 VR. I made some home tests and provide the results below. In addition to back-focus, what is happening? Which is the reason for the lack of detail ? Is this normal?

Edit:

I did some tests with basic material. I used My D7200, D3100, the kit lens 18-140mm f/3.5-5.6, the 70-200mm f/2.8 and the 24-70, with Live View, Manual Focus, a tripod with a level in the camera and the settings below. I used a diagonal test chart and a perpendicular one which you can see here or download here. The JPGs are the conversion in Darktable of the NEFs without any adjustment. There are also the NEFs in the link.

The settings:

• Diagonal test chart
  • D7200
    • 1A _ 24-70mm f/2.8 _ 70mm, f/2.8, 1/500, ISO 100
    • 1B _ 24-70mm f/2.8 _ 70mm, f/2.8, 1/500, ISO 100 _ +20 AF Fine tune
    • 1C _ 18-140mm f/3.5-5.6 VR _ 70mm, f/5, 1/125, ISO 100
    • 1D _ 70-200mm f/2.8 VRII _ 70mm, f/2.8, 1/250, ISO 100
  • D3100
    • 2A _ 24-70mm f/2.8 _ 70mm, f/2.8, 1/800, ISO 400
    • 2B _ 18-140mm f/3.5-5.6 VR _ 75mm, f/5, 1/250, ISO 400
• Perpendicular test chart
  • D7200
    • 3A _ 24-70mm f/2.8 _ 70mm, f/2.8, 1/125, ISO 400
    • 3B _ 24-70mm f/2.8 _ 70mm, f/4, 1/60, ISO 400 (this for a bigger depth of fild)

It also has a back-focus issue that I tried to fix without success. One of the tests is purposely +20 and presents no difference.

Answer 1

All of the linked images appear to have camera motion as a factor in the overall sharpness of the image. They also seem to demonstrate the result of fairly aggressive noise reduction which can reduce the detail in an image. What shutter speeds were being used? What ISO setting was selected? Was the camera on a stable mount or being handheld? It appears the camera is changing positions slightly in each frame with each lens.

To accurately measure lens sharpness you should have the camera locked down and manually focused (i.e. via Live View at 10x magnification) on a flat target parallel to the camera's image sensor and perpendicular to the optical axis of the lens. This eliminates motion and focusing errors as the cause of any blurriness. You also need to conduct lens tests in plenty of light to reduce the effect of noise in the test images. "Locked down" means mounted on a tripod or other stable structure. It also means using a remote release or timed shutter release and either using a shutter time faster than about 1/200 second or using mirror lockup to eliminate internal vibrations in the camera.

To properly measure and calibrate AF performance you should also have the camera locked down and aimed at a well lit target perpendicular to the lens' optical axis with the tilted scale(s) to the side(s) of the target. Attempting to focus on a tilted target is susceptible to targeting errors. Hint: Those little squares in the viewfinder are not the total area covered by each AF point. The camera will attempt to focus on the area of highest contrast anywhere within the active area(s) of the AF system. And all other things (i.e. contrast) being equal, it will almost always focus on the nearest thing within the active focus area. That's why tilted targets are useless for calibrating AF. You think the camera is trying to focus on the bullseye in the middle when it is actually focusing on a spot closer to the camera.

For more about calibrating your AF system please see:
How can lens cause consistent front or back focus?
Which offers better results: FoCal or LensAlign Pro?
How can AF adjustment be inconsistent across lenses?

More about lens variation and manufacturing tolerances:
This lens is soft and other myths
When a lens and camera are callibrated together, which is changed, and might other lenses be adversely affected?

More about how (fast) lenses tend to be softest at their widest aperture:
Will using a lens at max aperture ("wide open") result in poor images?
Why are images with my Nikon D7000 and 70-200mm lens soft?

General techniques to obtain sharp images:
Why are my photos not crisp?
How can I hold my camera steady?
Focus problem vs. motion blur vs. camera shake - how to tell the difference?