by Ian Burley
The new, larger, Four Thirds sensor from Panasonic makes wider format shooting more efficient
It may look very similar to a DMC-G1, but Panasonic's new DMC-GH1 has new, larger, Four Thirds sensor.
It's widely assumed that the Four Thirds image sensor size is fixed at 18x13.5mm. But the truth is that it can be any aspect ratio as long as the sensor diagonal, which is the same as the Four Thirds image circle, remains 22.5mm. By coincidence, Four Thirds has standardised on a 4:3 frame aspect ratio. The system name 'Four Thirds' does not relate to this at all. Instead, Four Thirds is a reference to the chip carrier size and, in turn, distantly relates to video camera tube sizes, four thirds inches, in the early days of video cameras.
The fact that you could implement a sensor chip of any aspect ratio for Four Thirds was something confirmed to me by Olympus engineers right at the beginning, when the first Four Thirds camera, the Olympus E-1, was launched. Later, when Panasonic replaced Kodak as the primary supplier of sensors for Four Thirds cameras, I soon discovered that Panasonic was keen to explore the possibility of a Four Thirds sensor that would enable user-selection of a variety of frame aspect ratios. I was asked to keep this under my hat, which I have done until now, because the new Lumix DMC-GH1 is the first (Micro) Four Thirds camera to deliver on the variable frame aspect ratio promise - without simply cropping a 4:3 frame. Panasonic has already produced the DMC-LX1 compact camera, the first compact camera to be fitted with a 16:9 'wide screen' CCD sensor.
A wider sensor is better
The Panasonic Lumix DMC G1 and Olympus' E-30 and E-620 models all offer different aspect ratio frames for the user to choose from, but non can be wider or taller than the basic 4:3 aspect ratio frame, which is representative of the actual sensor physical limits. However, the Lumix DMC-GH1 breaks out beyond those limits thanks to a new over-size Four Thirds compliant sensor. Proof is in the pixel dimensions of the various optional frame choices:
|1:1||N/A||3024x3024 9.1MP||2992x2992 9MP|
|4:3||4000x3000 12.0MP||4032x3024 12.2MP||4000x3000 12.0MP|
|3:2||4000x2672 10.7MP||4032x2688 10.8MP||4128x2752 11.4MP|
|16:9||4000x2248 9.1MP||4032x2272 9.2MP||4352x2448 10.7MP|
In all but the 1:1 aspect (square frame) choices, the Lumix G1 and Olympus E-30 and E-620 are limited to the maximum width of the 4:3 sensor area. But the Lumix GH1's sensor goes wider than the width of its 4:3 aspect frame for 16:9 and 3:2 frame formats.
The diagram above shows the Four Thirds image circle and how the typical Four Thirds 4:3 frame fits within it. Please note that the effective dimensions of a 4:3 Four Thirds frame are slightly smaller than 18x13.5mm, at 17.3x13mm.
In this diagram (above) the blue area shows a 16:9 frame on a Lumix DMC-GH1. The wider sensor enables the 16:9 format to fill the maximum area under the Four Thirds image circle.
Finally, the red area shows the limited area of a 16:9 frame that Lumix DMC-G1 and Olympus E-30 and E-620 users have to make do with compared to the unrestricted blue area thanks to the larger sensor of the GH1.
Panasonic has chosen not to publish any dimensions for the sensor in the GH1, but we can logically estimate it to have the width of the 16:9 format and the height of the 4:3 format frame areas, making it 4352x3000 pixels, or about 10:6.9 (about 18.8mm x 13mm), a total of 13.1 million available pixels, instead of 17.3x13mm and 12.1million available pixels..
The benefit at 16:9 is around 1.5 million pixels, and just over half a million pixels for 3:2 (35mm film frame format). It shouldn't cost much more to manufacture such a chip, so it's not unreasonable to expect it to be rolled out beyond the GH1, in future Panasonic models.
It would seem logical that Olympus should follow the Panasonic lead in employing this new, larger, Four Thirds sensor, at some time in the future, perhaps with the expected successor to the Olympus flagship E-3 DSLR, and with the forthcoming Olympus Micro Four Thirds cameras.
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