0

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.

  • 2
    It looks like the focus target in your first image is not fully perpendicular to the film plane, as the left side is noticeably softer than the right. It is less likely that this is a lens fault than positioning error, though the former is certainly possible. – HamishKL Apr 13 '16 at 6:20
  • 1
    Was the camera on a stable mount or being handheld? It appears the camera is changing positions slightly in each frame with each lens. – Michael C Apr 13 '16 at 11:24
  • The machine is resting on the table with a book under the lens. I know that the target is not perpendicular, but even when I point directly to the letters at the same level, the result is identical. The 70-200, under the same conditions, shows best results. Anyway, I will repeat the tests in decent conditions, as soon as I return to base. Thank you. – Sardinha Apr 13 '16 at 22:31
  • On your edit and samples: with your diagonal test chart, there's no clear target to focus on. The actual area of the focus sensor is much larger than that of the focus point indicator light (and "point" is definitely a misnomer). You need a separate target, as used in for example the lensalign. In any case, with that or with the perpendicular target, can you try focusing with contrast-detect in live view as a comparison? – mattdm Apr 23 '16 at 22:50
  • 1
    All of the links are dead. – Michael C Mar 14 '17 at 7:52
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?

  • The machine is resting on the table with a book under the lens. It is true that the conditions are not good, but the results in the field are identical. If you point directly to the white area of the target, it keeps hunting and doesn't lock, so it will most likely use the area between white and black. I will repeat the tests, in decent conditions, soon I have the opportunity. I'll have to override the variables that you mention. Thanks for the readings and the answer. – Sardinha Apr 13 '16 at 22:57
  • Here are 2 shots I taked at dinner, before work, with ISO 1600, 48mm, f/2.8, 1/125 and f/4, 1/60, Noise Reduction off. The focus is in the border of the left glass. Hand helded. dropbox.com/sh/an3x5lqpf5s0imj/AABc95giAWIhd1sYVXsC4Pp3a?dl=0 – Sardinha Apr 13 '16 at 23:52
  • 2
    You need to take your test shots under enough light that you cans shoot at ISO 100-200 and at shutter speeds above 1/400 second so you can eliminate other contributing factors. – Michael C Apr 14 '16 at 4:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.