[B][COLOR=darkgreen]No.6[/COLOR][/B]: What makes Four Thirds special?

I'm often asked why I have a special interest in Four Thirds. I must emphasise that my fundamental interest is in taking pictures and photography in general, regardless of brand or system platform. But ever since Olympus introduced the OM system in the mid-1970s, I have marvelled at how Olympus has applied its engineering in a re-inventive way. That philosophy remains as true today as it has been over the last 50 years.

Although Four Thirds is not limited to Olympus, it was conceived by Olympus. Panasonic Lumix is credited with adapting Four Thirds into Micro Four Thirds, and again we see a re-invention of the technology.

Apart from Four Thirds, all the main digital SLR systems are based on platforms originally designed for film. To quote an over-used slogan, Olympus designed Four Thirds to be 'designed for digital'. Olympus decided to start from scratch with its all-digital Four Thirds system, and avoid any compromise imposed by adapting a film system to digital.

[B][COLOR="DarkGreen"]Key aspects of Four Thirds:[/COLOR][/B]

[COLOR=darkgreen][B]1. Over-size lens mount:[/B][/COLOR] In order to provide the ideal illumination of a digital sensor, the exit pupil of a lens needs to be larger in relation to the size of the sensor than a film camera. This requires a much wider lens mount.

[B][COLOR=darkgreen]2. Designed for digital lenses right from the start:[/COLOR][/B] Many lenses from DSLR manufacturers are based on, or remain, old designs for their old film cameras. It's possible to use a wide variety of 'legacy' lenses on a Four Thirds camera via a mount adapter, and many users will attest that even those older lenses that were regarded as excellent for film often fall short when used on a digital body. The way a digital sensor captures light from a lens is different to that of film, especially the closer to the periphery of the frame. Lenses designed for digital, in conjunction with a wide lens mount, exhibit less vignetting, more consistent resolution into the corners, and less fringing. It's even claimed that as less light is reflected from the surface of the sensor, effects like ghosting can be reduced.

[COLOR=darkgreen][B]Size and weight:[/B][/COLOR] Four Thirds uses a sensor size that is around a quarter of the area of a 35mm film 'full frame'. More accurately, the image circle diameter is half that of full frame 35mm. This means you can halve the focal length of a lens and still have the same field of view as a 35mm format lens. Halve the focal length and you can, in theory, halve the size and weight of the lens. In reality, the size and weight saving is more like a third, but it's still substantial. Or, you can have a faster (brighter) lens for the same weight and size. The benefit extends to the size of the camera body, too, as demonstrated by the very compact E-400 series and the E-620.

[B][COLOR=darkgreen]Fly by wire manual focus:[/COLOR][/B] Another innovation we associate with Four Thirds is fly-by-wire manual focusing control. This is not universally loved, but it does avoid the perennial issue of cheaper lenses suffering from nasty mechanical manual focusing rings.

[B][COLOR=darkgreen]Open standard:[/COLOR][/B] Four Thirds is an open standard. This persuaded Panasonic Lumix to adopt the standard instead of inventing their own. The independent lens manufacturer, Sigma, is also a signatory to the standard. Other names linked with Four Thirds, if not actively in recent times, include Sanyo, Kodak, and Fujifilm. Leica even sold a re-branded Panasonic Lumix Four Thirds DSLR, and its name continues to be a brand on certain Panasonic designed and manufactured Four Thirds lenses.

[COLOR=darkgreen][B]Super Sonic Wave Filter:[/B][/COLOR] All Four Thirds cameras are fitted with a very effective measure that deals with dust particles that might otherwise spoil images. Firstly, a filter is employed behind the reflex mirror of Four Thirds DSLRs to protect the sensor. This mirror is relatively far from the sensor plane, so any stubborn dust will usually be invisible as it won't be in focus. The filter is also subjected to high frequency vibrations, which induce a wave form in the filter, flinging the dust off its surface by focusing energy into the rippling wave action through the filter. This is the [COLOR=darkgreen][B]SSWF[/B][/COLOR], or Super Sonic Wave Filter. It's the most effective DSLR anti-dust system on the market.

Other innovations that are associated with Four Thirds cameras, if not precisely specified in the standard itself, include the introduction and evolution of [COLOR=darkgreen][B]DSLR live view[/B][/COLOR], and the adaptation of Four Thirds into a new platform for smaller and lighter cameras and interchangeable lenses, called Micro Four Thirds.

[COLOR=darkgreen][B]Negative perceptions:[/B][/COLOR] Four Thirds has not been enthusiastically embraced by everybody. To start with, it's not easy to persuade those that have invested heavily in existing rival systems to switch to a much newer one. Another perception is that the relatively small size of the Four Thirds sensor means image quality must surely be compromised. In truth, the area of a Four Thirds sensor is not radically smaller than an APS-C type sensor as used in most other low and mid-range DSLRs. Undeniably, Four Thirds has not enjoyed the cream of the crop in terms of sensor technology, though there are strong signs that the gap between Panasonic, which is now the main supplier of sensors for Four Thirds and Micro Four Thirds cameras, and the likes of sensor rivals Sony and Canon, is narrowing.
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[B][COLOR=darkgreen]Tomorrow:[/COLOR][/B] Selective focus tips for live view Olympus E-System users.