Concepts and overview


2003: The birth of a new Olympus SLR System
In 2002, the same year in which the Olympus OM manual focus, film-based SLR system was terminated, a whole new system and lens mount standard was announced: the digital E-System, based on the open "Four Thirds" lens mount standard. It came on the market in 2003, featuring the E-1 camera body, and a relatively small (at least compared to the OM System) set of lenses and accessories. In between Olympus didn't have any SLR system. It had Point & Shoot Cameras and a couple of Zoom Lens Reflex (ZLR) Cameras: the film-based iS-5000 and iS-500 (see the iS/L Series Page for the ZLR concept), and the digital Camedia E-10, E-20(N) and E-100RS. These last three models were, despite their "E" names, not part of the E-System. First, E-System camera bodies don't carry the Camedia designation. Second, ZLR cameras have a built-on non-exchangeable lens and therefore can't be true System Cameras. The Camedia E-10 (introduced in 2000) and Camedia E-20(N) (introduced in 2001) were reflex cameras, with an optical Through The Lens (TTL) viewfinder; the Camedia E-100RS had an electronic viewfinder. The E-10 and E-20(N) could be considered as predecessors of the E-System - they supported the external FL-20 and FL-40 flashes which are compatible with the E-System bodies; vice versa the new FL-36 and FL-50 flashes can be used on these cameras. 

One might wonder why Olympus terminated the OM System and created a whole new system and lens standard. Would it not have been easier to make a digital AF OM-mount compatible body and  reintroduce some of the AF lenses for the only AF OM body Olympus ever made, the OM-707 AF? After all, Nikon and Canon did the same - they kept the existing analogue lens mount standards and built digital bodies for them. The answer from Olympus was that lenses designed for film based photography are not optimized for digital photography. When a lens designed for analogue photography is used, light falls onto the sensor under an angle, which reduces sharpness, especially in the corners, especially for wide angle lenses.

Four Thirds
The Four Thirds lens standard was designed by Olympus and Kodak as an open standard, meaning that any company may adapt it and create bodies or lenses for it. The standard describes the mount size, sensor size, mount-to-sensor distance and electronic communications between lens and camera. The idea alone of an open standard lens mount is revolutionary - until then every SLR camera manufacturer had its own standard.  
The term Four Thirds comes way back from the 1950's when it described the outside diameter of vacuum valves for video recording, called Vidicon. This  was four / thirds of an inch (33.87 mm); this is also the outside diameter of the Kodak sensor KAF-5101CE featured in the E-1. The rectangular sensor has an inner diagonal of 22.3 mm, measuring 18 x 13.5 mm. This diagonal is roughly the half of 35 mm film (dimensions 36 x 24mm, diagonal 43.3 mm). 

This size means that focal lengths for Four Thirds lenses are also the half of the 35 mm lenses.
This, in combination with the relatively large diameter of the lens mount, makes it possible to design fast lenses that are much smaller and lighter as corresponding 35mm film lenses, and even to design lenses that are faster than 35mm film lens design would allow. A 300mm/F2 lens, 600mm/F2.8 lens or 2.5-3x zoom lenses as bright as F2 are examples of this; such lenses would be impossible to design for 35mm (or else they would be huge,  heavy and extremely expensive) - they do exist in the E-System!
Compare, for instance, the digital Zuiko  ED 150mm/F2 (corresponding to 300mm/F2 for 35mm film) to the longest F2 lens ever made for 35mm, the Zuiko 250mm/F2 for the OM System. The first has a length of 150mm and weighs only 1610g. The latter had a length of 246mm and weighted 3900g! And its focal length was shorter too. There's also an interesting difference in price: the first costs 2000 Euros, the latter cost in 2001 13.450 Euros...

Telecentric design
All digital Zuiko lenses feature a telecentric design. This means that light strikes the sensor at a right angle for all focal lengths. This improves image quality since photo sensors can't handle light that hit them under an angle other than 90 degree very well. This is especially the case when wide angle lenses designed for 35mm photography are mounted on a digital camera. Blurring and shading may occur with such lenses.

Supersonic Dust Filter
Another novelty that was introduced in the E-System was the Supersonic Dust Filter  - placed between the shutter and the sensor, it is activated when the camera is turned on. It vibrates a high speed and removes any dust from the sensor. Dust is a major problem with digital SLR cameras, since it's difficult to avoid when changing lenses in rough conditions, difficult to remove by the user and can have serious impact on image quality. 


page under construction; last update: september 24, 2005