You probably enjoy opening your lens to its widest aperture sometimes subject-isolating depth of field and that smooth bokeh. Of course, with that thin depth of field comes a thin margin of error for focus. If you’ve been careful about your focus points, you have good light and your technique is sound, but you still have a lot of out of focus shots, your lens and body might need an autofocus microadjustment.
Often, a camera body and lens will focus precisely, but not accurately. This means there is a consistent error in which the lens focuses too far forward of the subject or too far behind (i.e., the lens front focuses or back focuses). The key that allows us to correct for this error is that it is consistent; if we can measure its size and which direction it falls in, we can compensate for it by applying an equal and opposite correction. This becomes particularly important at wide apertures, where depth of field is so small that an error of a few centimeters in either direction can be the difference between making a shot and making a mess. Autofocus microadjustment (AFMA) allows us to make that correction by programming your camera body to consistently apply a compensation whenever that lens is attached.
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