Four Thirds 101

A Brief Introduction to Four Thirds

This article introduces some of the concepts behind the Four Thirds standard, its history and explores some of its strengths and weaknesses.

What is Four Thirds?

Four Thirds is the collective name for the camera system comprising compatible DSLR camera bodies, interchangeable lenses, accessories, and software. Originally conceived by Olympus, in the form of its unique, designed-for-digital E-System, launched in 2003 with the Olympus E-1 semi-professional specification camera, Olympus found it difficult to meet the monumental challenge of establishing the brand new E-System as a successful alternative to other camera manufacturers, including Canon, Nikon, Pentax, Sigma Fujifilm, Kodak, and others who simply, and relatively inexpensively, adapted their 35mm film camera systems to digital.

Olympus had all but quit the mass-market 35mm film SLR market in the early 90s after deciding not to upgrade its manual-focus OM-system for the market demand of autofocus SLR cameras. Therefore, Olympus had the advantage of launching into the up and coming digital SLR age with a clean sheet. The result was the E-System, with Kodak supplying sensor chips and both Fujifilm and Sanyo signed up as technology partners.

Right from the start, Olympus realised that it would need key partners to ensure the success of its E-System platform and the Four Thirds brand, which Olympus declared as an open standard, was used from the start. Sanyo is a major independent manufacturer of cameras and has been an OEM manufacturer for many of the top Japanese brands. Fujifilm's involvement in Four Thirds has always been difficult to pinpoint.

Later, Panasonic was signed up to Four Thirds, providing a massive technological and marketing boost for Four Thirds, further underlined by the addition of commitment from lens and flash system manufacturer, Sigma.

Panasonic has now replaced Kodak as the primary supplier of sensor chips for Four Thirds cameras, and Panasonic has also introduced its own Four Thirds camera model, the Lumix DMC-L1. Under the skin, this was a joint development between Panasonic and Olympus, both using Panasonic's new MOS-technology sensor. Olympus produced the visually very different and much more affordable, but technically closely-related E-330, which made history by being the first digital SLR camera to offer a live, through the lens, view for accurate composition and critical focus, using its colour LCD screen. Introduced after the E-330, Panasonic's DMC-L1 also offers live view and is sold with a Leica-branded but Panasonic designed and manufactured lens standard zoom lens, incorporating optical image stabilisation. The DMC-L1 was proof of further development of Panasonic Lumix's close digital camera design relationship with Leica Camera AG. Leica now sells a slightly-redesigned version of the Panasonic DMC-L1, called the Leica Digilux 3.

Meanwhile, Sigma, while persevering with its own proprietary SLR system, started to produce Four Thirds-compatible versions of its more popular lenses, providing additional choice for Olympus, Panasonic and Leica Four Thirds camera users.

What does Four Thirds actually mean?

Instead of preserving the film SLR tradition of an image frame with the aspect ration of 3:2 (width:height) Olympus decided that the 4:3 aspect ratio as used in the vast majority compact digital cameras was the way to go. However, this is a confusing red-herring when it comes to the true meaning of 'Four Thirds'. The term actually relates to the size of the sensor that lies at the heart of the Four Thirds standard. The chip that Olympus settled on is categorised using a video tube sizing standard as 4/3rds inches. In fact, the physical area of Four Thirds sensors used to date is roughly a quarter of the old 35mm film frame, using a frame diagonal half that of the 135 film 'full' frame. This has one benefit if making it very easy to calculate the equivalent 135 full frame focal lengths that matched the field of view of Four Thirds lenses. You just need to double the actual focal length of a Four Thirds focal length, so a 14mm Four Thirds lens had the same angle of view as a 28mm lens for full frame 135 format cameras.

What advantages does Four Thirds offer?

Four Thirds is still the only DSLR system standard designed from scratch to be a thoroughbred digital platform. In relation to the size of the sensor, the Four Thirds lens mount is huge, enabling a large diameter rear lens element to cover the sensor area and minimise a significant issue experienced with lenses designed for film when used on digital sensors. With lenses like these, designed with relatively under-sized rear elements, sometimes too close to the sensor, the physical characteristics of the surface of a digital sensor, made up of millions of microscopic light sensitive pits, reduced light collecting efficiency towards the corners of the frame ushered in a new term: corner shading. Besides darkening in the corners, lenses not optimised for digital sensors could also cause reduced sharpness and chromatic aberration, or fringeing. Olympus knew about these issues and formulated the Four Thirds lens mount diameter, sensor size and distance between mount and sensor to minimise corner shading.

Even with the inherently reduced risk of corner shading, Four Thirds uses a sophisticated communications protocol between CPUs in the lens and body that. among other things, can theoretically communicate information about the corner shading characteristics of the lens and so enable the camera body to compensate accordingly.

It looks like all future Four Thirds camera models will feature live view mode, which is still a rarity in rival models.

All Four Thirds cameras manufactured to-date incorporate an Olympus innovation called a Supersonic Wave Filter that literally shakes dust particles off a clear filter in front of the camera's sensor using a high-frequency vibration that effectively ripples the filter, flinging the dust off its surface. According to independent tests, the Supersonic Wave Filter is more effective than other 'shaker' systems.

The Four Thirds sensor is the smallest of all current DSLR platforms.This enables lenses of equivalent viewing 'power' and brightness to be as little as half the size and weight as respective lenses designed for full frame cameras. Olympus has also used the same size advantages to produce the smallest DSLRs to date, the diminutive E-400 and E-410 models.

Ironically, despite a relatively limited choice of camera body specifications, Four Thirds users enjoy a healthy selection of high quality lenses from Olympus, Sigma and Leica, with more in the pipeline. Most are of above average optical quality and several are pro-spec., with weather-proof sealing and robust construction. It should be noted that many of the high-specification lenses on offer aren't cheap!

Mechnical refinement is a traditional, consistent, plus in Four Thirds camera models. Compared to some key rival brand models, shutter and mirror action is smooth and quiet.

Finally, Olympus and Panasonic are always innovating. Some of these innovations work better than others, but arguably there have been more DSLRs innovations through Four Thirds, especially in the consumer end of the market, than any other system.

What are the perceived disadvantages of Four Thirds?

With the smallest DSLR sensor size and a history of below-average noise performance, Four Thirds has earned criticism that the sensor size is fundamentally too small. Technically speaking, that's nonsense because the Four Thirds sensor size is only marginally smaller than Canon's APS-C DSLR sensor, used in its EF-S compatible camera models and these cameras have a reputation for particularly good noise performance. In reality, until recently, perhaps inherently noisy sensors or relatively unsophisticated in-camera image data processing, or a combination of the two, can explain the historic linking of Four Thirds with noisy images at higher ISO levels, but Olympus and Panasonic have progressively improved their sensor technology and the latest models are now substantially improved in this respect. High ISO noise is now on a par with Four Thirds rivals.

With its smaller sensor size and lenses, the view through optical through the lens viewfinders in Four Thirds cameras is smaller than you may be used to. The view could be made larger, but at the cost of brightness. Most people don't find the viewfinder a problem once they get used to it.

Autofocus performance and sophistication is not a Four Thirds strength and neither is its flash system. AF has, to date, been limited to just three points and although most Four Thirds lenses have quiet in-lens AF motors, they haven't been as fast, precise and quiet as ultrasonic motor AF systems, in particular Canon's USM technology. But the good news is that sonic technology will be introduced by Olympus in selected lenses later this year. The Four Thirds flash system is competent enough, but lacks advanced features taken for granted by Nikon, Canon and Sony users, like multi-unit wireless slave support.

Although the Four Thirds system was launched with a semi-professional model, the Olympus E-1, this model is now obsolete and there have been no professional-standard models since, to replace it. There is a pent up demand for a new model featuring robust, weather-sealed construction and fast shooting rates, with extended portrait mode grip designs. There have been plenty of rumours that Olympus will soon meet this demand, but until those rumours are realised, the Four Thirds choice remains entry-level to mid-range in terms of price and sophistication.

One advanced feature of most Four Thirds lenses is the implementation of fly-by-wire manual focusing. The focus ring is not mechanically connected to the lens mechanism, so the AF motor is electronically controlled instead. Why is this feature included in a list of perceived disadvantages? Well, not everyone finds this as positive to use as a good mechanical manual focusing arrangement. It works better on some lenses than others, it has to be said and, conversely, there are plenty examples of modern AF lenses that offer a poor manual focus option. It's not possible to find closest focus or infinity by 'feel', though the user can choose which direction to focus towards infinity or closest focus. All Olympus and Leica Four Thirds lenses use electronically controlled manual focusing, but until now all of Sigma's Four Thirds compatible lenses use a mechanical arrangement.