Since writing this, I have made a review based on using the actual product.
Contrary to what some people say, I actually find this lens pretty interesting. Some say that Panasonic should rather spend the time developing "real" lenses. However, I think that this lens might have some real creative potential, and it also serves to bring more interest into the Micro Four Thirds system. So what's not to like?
Focal length
The lens is specified to have a focal length of 12.5mm. However, don't let that fool you into believing that this is a wide angle lens. Far from it. The two separate lenses project image circles that are smaller than the full sensor. Hence, there is an additional crop factor to take into consideration.
The field of view is comparable to a 65mm lens on traditional 35mm cameras, corresponding to 32.5mm on Four Thirds cameras. Hence, this is a long normal lens. Observing that 32.5 / 12.5 = 2.6, we can conclude that this lens has an additional crop factor of 2.6, beyond the crop factor of Four Thirds lenses, which is 2.
On the Panasonic Lumix GH2, the lens produces stereo images of 2048x1536 pixel resolution. With the GH2 having 4602x3456 pixels, this means that each of the two stereo images comprise 20% of the image sensor. Here is an illustration:
Aperture
With a fixed aperture of f/12, the lens gives a deep depth of focus. Which is good for a lot of applications. On the other hand, at f/12, you will need to push the ISO up unless being outside on a sunny day.
3D effect
Obviously, the 3D effect is achieved by having the two separate lenses seeing slightly different perspectives. The lenses appear to be very simple constructions, with four lens elements in three groups.
The stereo base, the offset between the two lenses, is 10mm, corresponding to about half of the sensor width. This looks like a very short distance, and I am unsure if any significant 3D effect can be achieved with this short lens offset. Perhaps the 3D effect can be boosted in post processing?
Usage on non-compatible cameras
When used with a 3D compatible Micro Four Thirds camera, you can probably use the lens in a seamless fashion. The viewfinder will probably not show a confusing picture like the illustration above, but rather one of the subsections, to make framing easier. Compatible cameras at the moment include Panasonic Lumix G2 and GH2.
With an older, non-compatible camera, like G1, GF1, etc, I'm guessing the lens can be used like all others, with the exception that the two lenses will not illuminate the whole sensor. You may need to set the autofocus point to somewhere off centre, for that reason. Perhaps you will also need to change the exposure mode, since parts of the sensor are not exposed.
Of course, if the lens is used with non-compatible camera, i.e., anything older than the G2 or GH2, then you must convert the image into 3D in post processing.
