The technological differences between DSLRs and mirrorless cameras has just been narrowed with Nikon’s new AF Fine Tune feature, which is available at the moment only on the Nikon D5 and D500.
Ever since Minolta introduced integrated autofocus to the wider world with the MAXXUM 7000 back in February 1985, photographers have noted that occasionally their lenses aren’t focusing perfectly with specific bodies.
The problem is either identified as an front-focusing or back-focusing issue, meaning that there’s often a miniscule miscalibration between the lens and the camera. Previously on less powerful cameras the difference might not have been so obvious. But nowadays when photographers have access to 50-MP bodies and fast lenses with extremely shallow depth-of-fields, flaws are more evident.
DSLRs use a phase-detect system located under the mirror to achieve focus, and essentially the process is complex and involves a lot of variables. Any misalignments are immediately noticeable in this case, and will disturb autofocus performance.
While manufacturers of both DSLR bodies and lenses are extremely careful with their calibration tests, it’s inevitable that there are sometimes issues that occur. Hence most cameras have custom AF adjustments for individual lenses, although most photographers will have difficulty making these amendments themselves, as the calibration process requires absolute precision.
Mirrorless cameras don’t have this issue, since their autofocus information is drawn straight from the image sensor.
Nikon Auto AF Fine Tune
Nikon’s new Auto AF Fine Tune is so important because it makes calibration easy. Photographers don’t need any charts or external software to measure flaws in their lenses, and can simply let the cameras do all the work.
The Nikon D500 and D5 have contrast-detection autofocus systems for use with their Live View features, which are completely accurate. When the camera compares what their contrast-detection sensors measure versus their potentially inaccurate phase-detection sensors, they’ll note a discrepancy and offer an amendment.
DPReview have done a great video on this feature, which can be done with minimal effort.