What Is Autofocus Micro Adjustment? When Can It Help a DSLR?
What is autofocus micro adjustment?
Autofocus Micro Adjustment, often called AFMA, is a feature found on some cameras that lets the user make a small calibration adjustment to autofocus for a particular lens.
It is most relevant to DSLR phase-detection autofocus systems, where small alignment differences between the camera, lens and focusing system can affect where focus lands.
What are front focus and back focus?
Front focus means the camera consistently focuses slightly in front of the intended subject, while back focus means the focus lands slightly behind it.
The important word is consistently. One missed frame does not prove that a lens needs calibration. Subject movement, low contrast, shutter speed and autofocus mode can all cause apparent focus errors.
When can AFMA help?
If a compatible DSLR and lens combination repeatedly shows a consistent focus offset under controlled conditions, a small AFMA adjustment can sometimes improve accuracy.
Calibration may be useful for shallow-depth-of-field photography where even a small focus error is obvious, such as portraits with wide apertures.
When should you not use it?
Do not use AFMA as a first response to every blurry photograph. First check shutter speed, autofocus point selection, subject movement, lens condition and camera technique.
Also remember that some cameras use different autofocus systems in live view. A calibration setting designed for one focusing method may not solve every focusing issue.
What about mirrorless cameras?
Many mirrorless cameras use on-sensor autofocus systems that do not have the same front- and back-focus calibration issue associated with traditional DSLR phase-detection systems. The exact features vary by model.
If you are comparing a DSLR and mirrorless camera, check the specific autofocus architecture and calibration options rather than assuming AFMA is required.
Used-camera testing
When buying a used DSLR, consistent autofocus performance should be tested with the actual lens you plan to use. If a camera appears to need an extreme correction, investigate the body, lens and test method before assuming calibration is the answer.
A properly tested used camera should be evaluated across more than one subject and focus distance.
Final takeaway
AF micro adjustment is a specialised calibration tool, not a general autofocus fix. Use it only when controlled testing shows a repeatable focus offset on a compatible camera and lens combination.
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