AF fine tuning

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AF fine tuning

Postby Stany Buyle » Mon 30 May 2011 08:45

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:!: :!: :!: :!: Important note before reading further this topic: :!: :!: :!:

Legal disclaimer: The information written in this article are findings of a user, they are not meant as an official tutorial by any means.
The owner of this website nor the author of this topic have any responsability in possible problems, OOF images or loss of data you may encounter while using this method.

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:arrow: related topic on this forum: Lens AF-finetuning: Do YOU finetune your lenses and how?
:arrow: related topic on this forum: Very impressed with old version 28-75 F2.8 tamron on my D700 (after AF fine-tuning)
:arrow: related topic on this forum: My D700 AF fine tuning method, step by step... :idea: (*)
:arrow: related topic on this forum: Lens align from rawworkflow.com...




AF fine tuning was introduced at Nikon since D3 and it's an incredible feature. Once you master a good method, some lenses who seem to be garbage can turn into a lens that renders tack sharp images even wide open. My tamron that I bought for a bargain price together with a second hand fuji S5pro was a good example of what fine tuning can do ...

Recently I bought a Nikon D7000 with 18-105 kit and initially it produced quite soft images and even very soft when shot wide open. After fine tuning the 18-105 and my 105AF-S VR to -10 it renders perfectly sharp images.
Under while my AF fine tuning method has changed and improved though. I do not use the 45° focus chart anymore(*) while I found out it can fool the camera AF system and result in flawed conclusions.
The new method I use is done on a flat focusing target as expained here below with sample pictures.

step 1: Before doing anything else I double check if it is sure the camera or lens I'm examinating has a back-front focusing issue:
  • I put my camera with lens mounted perfectly aligned in height and paralel to the sensor surface to the target.
  • Switch to MF
  • Set your camera to aperture setting (A) and set the lens to the largest possible aperture for the most shallow DOF (lowest F-value).
  • Switch on LV and focus manually until you see the image perfectly sharp (while using maximum magnification in LV you can see better if it's sharp).
  • Switch on AF
  • Press the shutter half to see what the camera AF does...
    If you notice the AF module reacts by adjusting the perfectly obtained sharpness in MF, there might be a severe back or front focusing issue.

step 2: take test images from a very contrasty flat target which is perfectly aligned in height and paralel to the focal plane and sensor of your camera while using tripod, self timer and exposure delay mode.
take test shots at -20; -15; -10; -5; 0; +5; +10; +15 and + 20 AF fine tuning value(don't forget to save after every value) while re-focusing every time (I always force re-focusing by holding my hand in front of the lens and press AF button)

step 3: Compare the shots in Capture NX, bridge or any other image viewer or photo program
choose the AF fine-tune value which seems to give the sharpest image
Image


Step 4: Do another series of testshots while refining to 1 step each (f.i. -5; -6; -7; -8; -9; -10; -11)
Compare the shots in Capture NX, bridge or any other image viewer or photo program
choose the AF fine-tune value which seems to give the sharpest image

Step 5: save that value for that specific lens. Your camera will automatically recognise that specific lens when you mount it later again and apply the saved value.

Done.

Be aware that there might be subtle differences among test done in daylight and artificial light or flash. I always do bothg tests but the differences are subtle to none.

Even though professional developed tools for focus calbiration like lens align are easier to use and give more options, a simple bussiness card can serve perfectly as a test target for autofocus fine tuning:
(test images were taken while in camera sharpening set to 2 and "neutral" shooting mode)

A screenshot of a 100% crop of an image with D7000 and 16-85 without AF-fine tuning (value 0)
Image

And a screenshot of a 100% crop of an image with D7000 and 16-85 with AF-fine tuning value set to -17
Image



...
This topic will be continued....
kindest regards,

Stany
I like better one good shot in a day than 10 bad ones in a second...
http://www.nikonuser.info
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