Detection Autofocus Catches Up with Phase Detection

Professional photographers have so far frowned upon Contrast Detection Autofocus (AF) used in compact and mirrorless cameras, but that maybe about to change.

Traditional DSLRs used by professional photographers use phase detection AF, which till recently was considerably faster than contrast detection AF, albeit more expensive to implement since it required finely engineered mechanical components.

Contrast detection AF is both simpler and cheaper to implement.

he introduction of mirrorless cameras in end 2008 by Panasonic and Olympus proved to be a game changer in AF technology.

Mirrorless DSLRs are compact camera sized but have large sensors like traditional DSLRs, because of which the quality of their photographs is as good as those of DSLRs.

Mirrorless DSLRs achieve reduction in physical size by doing away with the bulky mirror-box assembly and optical viewfinder of a traditional DSLRs. Without the mirror-box they cannot implement phase-detection and are stuck with contrast detection.

In order to make mirrorless DSLR cameras acceptable, before introducing them to the market companies like Panasonic put in a lot of effort to improve contrast detection AF, and the effort has since continued since then.

Pansonic brands its mirrorless DSLR cameras as Lumix G Micro Systems cameras.

Contrast Detection Beats Phase Detection in Accuracy and Speed

Some of the new cameras of the Lumix G range are claimed to implement contrast detection AF that is faster and more accurate than phase detection.

For example, Pansonic's DMC GH-2 is claimed to have a 0.1 sec contrast detection AF time, which is as faster than phase detection AF. Fast contrast AF is achieved in the camera by reducing the detection time for focusing by doubling the drive speed from 60 frames per second to 120 frames per second.

According to Panasonic, its contrast detection autofocus is also more accurate than Phase detection, even when shooting at small F values.

Phase detection AF system is susceptible to mechanical margin of error, whereas contrast detection AF is controlled by the image sensor so has no mechanical margin of errors.

However, it is unlikely the Pansonic claim is true for low light conditions when contrast detection is difficult.