I must admit that I didn’t know a great deal about Topcon as a camera manufacturer before I bought this camera, but it seems to be a better quality manufacturer than a lot of the more famous makers. The film advance lever has a real feel that you are connected with a piece of precision engineering rather than just pulling on a lever connected to some cogs! According to the invoice for this camera I paid in 1972 the Unirex had a list price of $129.79, but was on sale for $99.95.
In design this camera is different from any other 35mm SLR I own because of a few interesting features. For example, the shutter is not a focal plane shutter sitting just in front of the film, but a leaf shutter sitting just behind the lens in the back of the lens mount. The shutter speed control is fitted around the back of the lens barrel behind the point where the lens mounts on the camera.
The ISO speed setting for the exposure system also sits at the same point, and this is also a bit unusual because it has different set points for different lenses. This can be seen in the picture above: there are 4 setting points for f/2.0 up to f/5.6. This makes me wonder if the setting had to be changed every time the lens was changed? That would be quite an inconvenience.
In a nutshell, it's an open aperture TTL metering, shutter priority auto exposure SLR, with a leaf shutter. It advanced the Uni specification by offering average metering switchable to spot metering for more demanding lighting situations. The spot metering area appears as a slightly darkened rectangle, within the fine focusing ring, and I suspect this is merely consequential to the mirror based CdS metering cell, rather than a design feature. The metering pattern switch is at the base of the rewind knob (which incidentally, doesn't also function as a back release - there's a separate release catch). Fully manual operation is also an option, either using - or ignoring - the viewfinder meter, which shows f-stop information for any selected shutter speed.
In common with the Uni there is a lens calibration dial, which is set when a lens is first fitted to the camera body, and this “communicates” the maximum possible aperture of the lens to the camera's metering system. On the Unirex, this simply requires the film speed setting to be aligned with a maximum aperture setting - from f/2 to f/5.6.
There is a slight difference between the Unirex and Uni exposure event sequence. While on the Uni, the mirror blocks the passage of light when the camera is not taking a picture, the Unirex employs an additional skirted film blind which folds and un-folds as the lens diaphragm closes and opens. Film blinds were quite common in early reflex cameras with leaf shutters. Due to all the bits that open, close and move, there's a quite noticeable blackout of the viewfinder when the shutter is tripped. Compared to other SLR cameras, it's a bit weird to see.
The standard 50mm lens has 6 elements (in an unknown number of groups), and a shiny chrome finish, matching the camera body. The camera additionally came in an all-black finish, with a matching black lens body. There is also companion model - the Unirex EE - which was produced between 1972 and 1974. This lacks the spot metering function, and came with a ubiquitous all black lens.