Olympus OM system
The camera included a full-aperture TTL Cadmium-sulphide (CdS) exposure meter, and a bayonet lens mount of relatively large diameter.
All the consumer-grade models were discontinued after 1992, since the market for manual-focus SLR cameras had declined greatly in favour of autofocus SLRs.
The Olympus OM-1 was a manually-operated 35 mm single-lens reflex camera forming the basis of the OM system in 1972.
It was designed by a team led by Yoshihisa Maitani with a through-the-lens exposure meter controlling a needle visible in the viewfinder.
One feature unique to the OM-1, compared to the rest of the OM system, was its mirror lock-up facility which made it ideal for astrophotography and macrophotography.
It boasted automatic through-the-lens (TTL) off-the-film (OTF) metering, and exposure was considered very accurate.
It used a horizontal cloth focal plane shutter with a speed range of 240s (in auto mode) to 1/2000s plus bulb, and flash X-sync of 1/60s.
The OM-4 featured a built-in spot meter [of a narrow acceptance angle, see Canon FTb] (2% of view; 3.3˚ with 50 mm lens) and was the first camera capable of measuring eight individual areas and averaging them.
The light meter used a dual-concentric segmented silicon photo-diode to provide spot or centerweighted readings.
It used a graduated linear LCD for the shutter speed at the bottom of the viewfinder to precisely indicate its readings versus the actual camera settings.
The OM-20 (sold in the United States as the OM-G) was essentially a refinement of the OM-10, replacing that model's rather tricky mode switch with one that was easier to use.
The OM-20 also had a built-in shutter-speed dial, a mode display in the view finder and a much stronger winding mechanism which permitted it to be used at 5 frames per second on the OM Motor Drive 2.
When used with a motor drive or winder unit and the M-In Focus Trigger cord, the lens could be pre-focused on a specific point.
During development, the Olympus design team led by Yoshihisa Maitani worked on a completely modular set of units called the MDN (Maitani-Darkbox-Normal), which resembled a 35 mm Hasselblad.
A more conventional camera which integrated the shutter, film transport, mirror and viewfinder was called the MDS (Maitani-Darkbox-Simple).
[4] The OM Series lenses had the aperture control ring located at the front of the lens barrel.
This was done to move it away from the shutter speed control, which was a ring on the camera body concentric with the lens mount.
