4/3 system, size, lenses and implications
The 4/3" type sensor measures 18.0 x 13.5 mm, just slightly smaller than the size of the CMOS sensors Canon have used in their EOS-D30, EOS-D60 and EOS-10D digital SLR's. That may come as a surprise to some as it can be difficult to visualize the size of a sensor. The diagram below shows the relative sizes of various sensors compared to a normal 35 mm film negative. Indeed what's interesting is that the 4/3 sensor is exactly half the width of a 35 mm negative, vertically the measurement is different because of the different aspect ratio.

The use of a smaller sensor means that you don't need such a large imaging circle (as would be produced by a 35 mm lens), this means you can make the lenses smaller and lighter, it also means that you can build lenses tailor made for the purpose, lenses which should perform better at wide angles.


(Diagram shown to scale but much larger than in real life)

What's probably more startling is the relatively minute size of the 2/3" type sensor used in the two previous digital ZLR cameras, the E-10 and E-20. The other implication of a larger sensor is larger photodiode sizes (larger pixel pitch - a measurement of the distance from the top corner of one pixel to the next). Larger photodiode size makes for lower noise and higher sensitivity, and looking at the table below we can see that the E-1's sensor has a photodiode size twice the size of the E-20 and just smaller than the sensor used on the EOS-10D.

Camera Sensor Total pixels Pixel pitch Sensor size
Olympus C-4040 Zoom 1/1.8" CCD 4.1 million 3.1 x 3.1 µm 7.2 x 5.3 mm
Olympus C-5050 Zoom 1/1.8" CCD 5.2 million 2.8 x 2.8 µm 7.2 x 5.3 mm
Olympus E-20 2/3" CCD 5.2 million 3.4 x 3.4 µm 8.8 x 6.6 mm
Olympus E-1 4/3" CCD 5.6 million 6.8 x 6.8 µm 18.0 x 13.5 mm
Canon EOS-10D CMOS 6.5 million 7.4 x 7.4 µm 22.7 x 15.1 mm
Canon EOS-1Ds CMOS 11.4 million 8.8 x 8.8 µm 36 x 24 mm
Kodak DCS-14n CMOS 13.8 million 7.9 x 7.9 µm 36 x 24 mm

Interesting note for the future: if Kodak could produce a 4/3 type sensor with a 2.8 µm pixel pitch it would have 31 million pixels, so there is plenty of scope for expansion at this sensor size.

Lenses and the lens mount
The other thing that the four thirds standard defines is the lens mount, communication protocol and other details relating to lens, zoom and focus. This is perhaps even more important, it means that in theory a Kodak four thirds camera could use Olympus lenses and that we may see third party manufacturers such as Sigma and Tamron producing their own four thirds lenses. Acceptance and wide ranger use of this open lens mount standard is vital to the survival of the four thirds system.

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