Olympus and Panasonic make contrast AF interoperable
** UPDATED 12th November, 2008

Firmware update policy now means all* contrast AF lenses will work on Olympus and Panasonic bodies, including Micro Four Thirds

Yesterday it was announced that Sigma Four Thirds, Panasonic/Leica D, and Olympus Digital Zuiko lenses will be able to be firmware updated when attached to Olympus or Panasonic Lumix bodies. Until now, you had to attach an Olympus lens to an Olympus body, etc., and there was no clear cut method for updating Sigma lens firmware.

All this is welcome news, but there is another story lying within. It's been a curiosity that the latest generation of contrast AF enabled lenses from Panasonic/Leica and Olympus have not been fully interoperable. But that's all about to change and ensures that all Four Thirds contrast AF lenses will also autofocus on Micro Four Thirds bodies, like the forthcoming Panasonic Lumix G1, using an adapter.

What is a contrast AF compatible Four Thirds lens?

When Panasonic Lumix launched their L10 DSLR in the second half of 2007, they laid claim to having launched the world's first DSLR that could focus in live view mode using contrast detect AF. This means that in live view mode, where the reflex mirror is raised and the shutter opened to expose the camera's imaging sensor, autofocus is determined by that sensor by making contrast measurements. at peak contrast in the region of the focus point selected, the image will be in focus. This is called contrast autofocus detect (AF). It's also the way most compact digital cameras focus.

Conventional SLRs use an entirely different system, called phase-detect AF, which is a range-finding system employing beam splitters and secondary focus sensors, and during operation the camera's reflex mirror needs to be down, obscuring the shutter and main sensor. This is why phase detect AF can't be used when using the main imaging sensor for live view.

The problem with contrast detect AF is that the gearing and stepping of the motor that adjusts focus needs to be very different to that for an AF motor optimised for phase detect AF. This is because Phase detect systems can predict the direction to and point of true focus, so the lens can be accelerated to that point at high speed. Contrast detection requires repeated stop/start action to sample the contrast of the focus point. Making a lens optimised for phase detect work like this slows the focusing action down dramatically.

Being pioneers of DSLR live view, both Olympus and Panasonic decided to develop contrast-detect optimised lenses. To date, these are:

  • Leica D Vario Elmar 14-50mm f/3.8-5.6 (the Panasonic DMC-L10 standard zoom kit lens)
  • Leica D Vario Elmar 14-150mm f/3.5-5.6
  • Leica D Summilux 25mm f/1.4
  • Olympus Zuiko Digital 14-42mm f/3.5-5.6 (E-4x0 and E-5x0 standard zoom kit lens)
  • Olympus Zuiko Digital 40-150mm f/4-5.6
  • Olympus Zuiko Digital 25mm f/2.8
  • Olympus Zuiko Digital 9-18mm f/4-5.6

Note: Some examples of these lenses may require a firmware upgrade to work in contrast detect mode.

All the Leica D models (with latest firmware) have worked on the E-420 and E-520 (which support live view AF) in contrast AF mode. However, the Panasonic Lumix DMC-L10 has only operated, until now, in contrast AF mode with the three Leica D lenses listed above.

But from now on, after upgrading both bodies and lenses to the latest firmware, all seven lenses* above should be able to work in live view contrast AF mode on either the Olympus E-420/520 or the Panasonic Lumix DMC-L10.

Not only that, but Panasonic and Olympus have confirmed to me that all these lenses will also autofocus on the forthcoming Panasonic Lumix DMC-G1 Micro Four Thirds body, via the supplied Four Thirds lens adapter.

What about other Four Thirds lenses?

Both the Olympus E-420 and E-520 employ a 'hybrid' live view AF mode that enables a Four Thirds lens that is not optimised for contrast AF to be auto-focused in live view mode. This system makes such lenses a lot more usable in live view mode, but the cost is that accurate focus must be determined using phase-detection, with the mirror down, after the shutter is released, which means additional shutter response delay, or lag. Panasonic has not yet offered such a facility for the L10 and it's not likely to be featured on the Micro Four Thirds G1, either. This means that apart from the current seven Four Thirds lenses listed at the top of this page, no other current Four Thirds lens can be auto-focused on the G1. I have asked whether manual focus with focus point confirmation will be implemented on the G1 with Four Thirds lenses and will update this article once I get a definitive answer. I would expect Olympus to include hybrid live view AF when it brings out its promised Micro Four Thirds models.

*12th NOvember, 2008: We now know that the 9-18 is G1 compatible - we tried it for ourselves!

Olympus firmware release news page.

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