How can I accurately micro-adjust autofocus for a back-focusing lens?
Asked 11/5/2012
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I’m using a Nikon D7000 and most of my Nikon lenses focus correctly, but a recently purchased Tamron 28-75 appears to focus behind the subject. I’ve tried changing the camera’s AF fine-tune setting experimentally, but I’m not sure how to determine the correct value.
Is there a reliable way to test whether a lens is front- or back-focusing and set the proper autofocus micro-adjustment?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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Place a ruler flat on a table, raise one end with an object to create a slope.
Erect an object that is thin and tall, a pencil maybe, at the edge of the ruler with readings, remember the position where the pencil touches the ruler(5cm for example)
Line up your camera so that :
The pencil is perpendicular to the lens
the ruler is in parallel with the lens barrel
Focus on the object, the reading (5cm) should be in focus.
Using a tripod may help.
If 4.5mm turned out to be sharp, the lens need to have its focus adjusted forward. If 5.4mm is sharp, adjust it backward.
This way you know if it is focusing in front/behind of the object, and you know roughly by how much (in mm), so you can adjust it accordingly (if the camera has such function).
Originally by user6745. Source · Licensed CC BY-SA 4.0
user6745
13y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. A simple way is to test focus with a slanted ruler and a clear focus target.
Set a ruler on a table at an angle by raising one end. Put a thin vertical object, such as a pencil, at a known mark on the ruler. Position the camera so the pencil is perpendicular to the lens, and the ruler runs away from it at an angle. Use a tripod if possible.
Focus on the pencil, then check which ruler marking is actually sharpest in the photo. If the sharpest point is in front of the pencil’s mark, the lens is front-focusing; if it is behind, the lens is back-focusing.
Then adjust the camera’s AF fine-tune setting and repeat until the pencil’s mark is the sharpest point. This gives you a practical way to find the correct micro-adjustment.
Depth of field extends in front of and behind the focus plane, but the point of best focus should still land on the target itself when autofocus is calibrated correctly.
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