Olympus Four Thirds dSLRs to remain with mirrors – and why it will be hard for Canon or Nikon to use existing lenses for a mirror-less system

Written by Gary on March 18th, 2010

Recently, a US-based Olympus representative suggested that the Four Thirds dSLR system may become mirror-less within 2-3 years.

However, this interview with an Olympus representative from Japan has negated this view and states that Olympus Four Thirds dSLRs will, by necessity, remain with the mirror dSLR and phase contrast detect AF system for quite some time yet.

The reason for this is the difficulty in getting current lenses, which are optimised for phase contrast AF, to work fast enough in a contrast detect AF (CDAF) system that is the ONLY AF system available to mirror-less cameras such as the Micro Four Thirds.

Certainly, current CDAF technology is not able to AF on fast moving subjects as can some phase contrast dSLRs – yet.

It would seem that for fast CDAF, the lens must have a small and light focusing group of lenses – and this implies that even bigger lenses such as those designed for Canon, Nikon, Sony, and Pentax dSLRs will have even more difficulty achieving fast CDAF.

It is logical then, that the smaller the sensor, the smaller the lens, the faster it is possible to make the CDAF – and this is one reason why I think Micro Four Thirds will have the advantage over APS-C sized mirror-less systems, in addition to smaller lenses, greater telephoto reach for size, greater versatility with lens adapters such as Leica M, tilt-shift adapters, AF-capable wide extender adapters, etc.

I am not sure I understand why he states that a CDAF-optimised lens needs to be wider and longer than a traditional phase-contrast AF optimised lens – I would have thought computerised design would be able to get around this.

Current Four Thirds lenses which are not CDAF-certified have very slow AF on Olympus Micro Four Thirds cameras and are manual focus only on Panasonic Micro Four Thirds camera.

I am not aware of any Canon or Nikon dSLR lenses which are optimised for CDAF and their cropped sensor lenses such as the EF-S ones are generally no where as good optically as Olympus equivalents which puts Canon and Nikon a long way behind the game in the fastest growing camera sector.

What he doesn’t mention though is if the Four Thirds mount will be modified to allow for the extra contacts of the Micro Four Thirds system to ensure future CDAF Four Thirds cameras and lenses would at least have a chance of having fast CDAF.

While they are at it, perhaps they should add in an extra contact so that one day they may design a power zoom for even better video capabilities.


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