A bit of history

Let's go back to 1972, when Olympus unveiled their new SLR camera, the M-1. It was smaller and lighter than other SLRs of the time, as the reduced size was one of the chief aims of the design team. It caused quite a stir, especially with the people at Leica, who objected to the M-1 and M System name. After all, they had been producing Ms for years. So, not long afterwards, the name was changed to OM. By then, quite a few M-1 cameras had left the factory - 52000 according to Olympus, and today any with that name on are worth quite a bit more than the OM-1 models which followed. Having said that, I saw one go on eBay for just £75 a few weeks ago, so you never know... 

Of course, a few unscrupulous people might try to pass an OM-1 off as a rare M-1 - switch or alter the top plate and it's done. So a couple of things to check are the base plate, which should only have a battery compartment and no motor drive door, and the pressure plate inside the back, which was only about 50mm long at first, going up to 60mm later.

 

The slightly more elusive M-1

As far as I can tell, the serial number, found on the bottom plate, started at 100000, but let me know if I have got that wrong. I have never seen one with a number less than that, and the early M-1s I have seen have all started with a 1. But having said that, it seems that the bottom plates were produced in large quantities, and used at random, so the serial number is not a reliable way to estimate the age of these cameras.

The early models had to have their bottom plate modified to take a motor drive, but in 1974 the plate was changed to give access to the motor drive mechanism inside. A small "MD" badge was added to the front of the camera, although some do turn up with the motor drive access but no badge.

Things stayed much the same until 1979, when the OM-1N appeared. It was pretty much the same as the OM-1, but with a slightly different film advance lever, and the ability to communicate with the Olympus T-series flash units. 

Production of the basic OM-1 ended in 1979, with the OM-1N going on until 1987.

By the time the original OM-1 was withdrawn, they had launched the OM-2 (1975, with added aperture priority auto mode, off-the-film metering, and electronic shutter), the OM-2N (1979, same changes as the OM-1N), and the OM-10 (1979, their first consumer-grade OM camera, with aperture priority auto and an optional adapter for full manual mode)

One thing to look out for when you are buying these early models is the state of the foam around the prism. When the OM-1 was first produced, some foam was added around the prism, to stop light leaking into the camera body. Some time later, apparently around the time of the serial number 1100000, the foam was left out, as it was thought to be unecessary. But it was re-introduced with the OM-1N, and remained to the end. The problem is, it rots, and attacks the silvering on the prism. The only solution is to remove the top of the camera, clean it out, and if necessary, replace the prism. If the rot has started to eat away at the silver, it will show in the viewfinder as dark patches, usually along the bottom of the image. Sellers will often say if they have removed/replaced the foam or prism, but others may not even know about the issue. If you can check the serial number and find it is greater than 1100000, you may be in luck and not have to worry.

For the OM-2, the story is much the same, with the serial numbers after 500000 being the foam-less models, but once again it came back for the OM-2N.

Further OM series models followed, both in the "professional" and "consumer" ranges, but I won't go into all of those. Needless to say, more features were added along the way, and the final OM-4 was produced in 2002. They were all fine cameras in their way, but for me the simplicity of the OM-1 wins.