Welcome to the world of mechanical auto exposure, whose cameras are today both collectable and usable.
At the heart of a camera’s automatic exposure system lie three basic procedures. First came shutter priority, in which the photographer chose a shutter speed and the camera automatically set the correct aperture. Then came the more popular aperture priority, allowing the photographer to select an aperture, leaving it to the camera to set the correct shutter speed. Finally, both shutter speeds and apertures were automatically chosen and set with programme (or program) mode. All of which took off big time when battery-driven electronics hit film cameras in the 1970s.
What you might not know is that automatic exposure modes like these go back much further, to the days when meters were activated by selenium cells that didn’t need batteries to operate, and when automation relied on mechanical levers, rotating cogs, expanding and contracting springs and even compressed air. Welcome to the world of mechanical auto exposure, whose cameras are today both collectable and usable.
1938: Super Kodak Six-20
The first camera to incorporate an electronic exposure meter was the Zeiss Ikon Contaflex in 1935. But that meter only recommended correct apertures against shutter speeds that then needed to be set manually. The first camera to use a built-in exposure meter to actually activate an automatic exposure system was the Super Kodak Six-20.
The camera incorporated two doors that opened from the front of the body, allowing the panel holding the Kodak Anastigmat Special f/3.5 lens to self-erect on struts, coupled to a wide-base rangefinder. It shot eight pictures 6x9cm on 620 size roll film. A large selenium meter cell stretched across the top of the body. Shutter speeds ran 1-1/200sec. Light on the meter cell produced the current needed to move a needle. First pressure on the shutter release then locked the needle in a comb-like device, while a sensor connected to the aperture control moved, adjusting the aperture as it did so until stopped by the locked needle. In this way the correct aperture for the chosen shutter speed, as indicated on a body-mounted scale, was set and the exposure was made.
Variations on this trap-needle method of exposure control, invented by Kodak, were later utilised by some other manufacturers to automate their own camera exposure systems.
1956: Durst Automatica
The Italian Durst company was best known for making enlargers. Less familiar are four different types of camera produced by Durst, of which this one became known as the first aperture priority camera.
The Automatica was very stylish and the first camera from Durst to accept 35mm film in standard cassettes. The film wind lever lay flush with the top plate, rising above the body only when winding. The rewind knob was equally flush and popped up when the rewind button was pressed. With a 45mm f/2.8 lens and shutter speeds of 1-1/300sec, the camera could be used manually when a lever beside the lens was set to ‘O’. Resetting the same lever to ‘A’ then twisting the shutter ring to its ‘300 automat’ setting put the Automatica into automatic mode. Here’s how it worked.
First the film speed was set from 6-400 ASA (ISO in today’s terminology) on a ring around the lens. This locked in an aperture which could no longer be changed. A speed of 6 ASA corresponded to f/2.8, then it was 12 ASA for f/4, 25 ASA for f/5.6, 50 ASA for f/8, 100 ASA for f/11, 200 ASA for f/16 and 400 ASA for f/22. The shutter worked by pneumatic air. Pressing the shutter button activated a plunger which built up pressure inside a small tube. It also released a meter needle to move across a scale depending on the level of light measured by the selenium meter. At the same time this moved a valve at the mouth of the pneumatic tube where a plate containing a variable sized slit moved according to how far the needle advanced. The width of the slit when the plate came to a stop controlled the length of time it took for the air to escape from the tube and therefore how long the shutter remained open. Result: automatic exposure.
1958: Bell & Howell Electric Eye
What appears to be the all-important selenium cell around the lens on this camera was actually no more than a piece of bevelled plastic, there probably to make the camera look more technically advanced than it actually was. The real cell was hidden inside the viewfinder with a gap in its centre so that the photographer could look through it when held to the eye.
As with many of these early auto exposure cameras, the shutter speed of Electric Eye was fixed at about 1/50sec. Setting the film type on a body-mounted thumbwheel caused a mask to swing in front of the meter cell to compensate for two different film speeds. The automation kicked in when light reaching the meter cell generated a current that was fed to a miniature voltmeter. Instead of moving a needle in the usual way, this rotated a gear linked to two overlapping slotted discs situated between the lens’s two elements. Each of the slots was tapered from wide at one end to narrow at the other. Their movement coincided to produce an aperture through which the image was recorded on the film.
The Electric Eye, which was also known as the Infallible, accepted its own dedicated flashgun. To adjust apertures for flash photography, the nameplate cover on the front of the camera was flipped up to reveal a sliding control marked with two distance scales, according to which film speed had previously been set. Sliding the control to the appropriate camera-to-subject distance changed the aperture, although actual f-stops were not indicated. This slider could also be used as a crude kind of manual exposure control.
1959: Paxette Electromatic
Carl Braun Camerawerk in Germany made a lot of Paxette cameras, with and without coupled rangefinders, with fixed lenses, with interchangeable lenses and finally this model, initially advertised as the world’s first fully automatic 35mm camera.
The description was perhaps a little over-stated, since the first version of the camera had only one shutter speed of 1/40sec, one film speed setting of 40/50 ASA and a fixed focus lens. Exposure automation came by the Kodak-inspired trap-needle method in which the selenium meter caused a swinging needle to be halted when correct exposure had been measured and, as the shutter button was pressed, for the aperture to change until the needle obstructed its movement. Red and green warning flags in the viewfinder indicated when light levels were suitable for shooting.
Unfortunately, Agfa took exception to the Electromatic being claimed as the world’s first fully automatic camera, took Braun to court, won the case and Braun was forced to withdraw the description from its advertising.
1959: Agfa Optima
The reason for Agfa’s angst was the Optima, launched within weeks of Braun’s Electronica. The Optima boasted automatic control of both shutter speeds and apertures, making it the first camera with programmed automation.
Beside the lens, what Agfa referred to as the ‘Magic Lever’ was positioned for a left-hand index finger. If a red flag showed in the viewfinder when this was depressed, light levels were too low for shooting. If a green flag appeared, the shutter button on the top plate was pressed and the exposure made. Inside, the aperture was initially set at its widest f/3.9 setting, remaining constant while light levels measured by the meter changed shutter speeds between 1/30sec and 1/250sec. If the light level was still too high when exposure reached 1/250sec at f/3.9, then the shutter speed remained at a constant 1/250sec while the apertures began closing down until they reached f/22.
For flash exposures, a tiny milled wheel below the lens was rotated from its ‘A’ for automatic setting to one that displayed a flash symbol. This caused a cap at the top of the faceplate to slide aside and reveal a flash synch socket, the magic lever locked and the shutter speed was set to a constant 1/30sec. Rotating a ring around the rear of the lens turned off the automation and allowed apertures to be set manually.
1961: Savoyflex Automatic
After making a few folding and simple viewfinder cameras from 1949 onwards, the French Royer company made its first single lens reflex (SLR), the Savoyflex, in 1959, upgraded it with a Model II soon after and finally arrived at the Model III, otherwise known as the Savoyflex Automatic. It was the world’s first shutter priority SLR, using a selenium cell above the lens which activated the aforementioned trap-needle method of automating apertures.
The camera had several peculiarities. It was sold with a small pouch of perforated plastic strips with different sized gaps cut into them. These were used to adjust film speeds by slipping them in front of the meter cell to lessen or increase its sensitivity. Focusing was achieved by shifting the optics back and forth and also by rotating the front element of the lens. In this way, the camera focused down to 30cm. Film advance tensioned the shutter, opened it for viewing purposes and lowered the mirror. The chosen shutter speed was set on a ring around the lens. Then as the left-handed shutter release was pressed, six things happened:
- the shutter closed,
- a flap moved across the viewfinder to block stray light,
- the mirror was raised,
- the automatic system selected and set the correct aperture,
- a needle swung across a scale in a window on the front of the body to indicate the chosen aperture,
- the shutter was released.
1961: Agfa Optima Reflex
Two years after the Optima, Agfa transferred similar automation into this unusual 35mm twin lens reflex (TLR). It looked like a conventional 35mm camera of the day, apart from having two lenses one above the other. The lower lens shot the picture, the upper one reflected its image to a pentaprism eye-level viewfinder which had a selenium meter cell mounted on the front. As the focusing ring was turned, the two lenses moved in tandem.
A ring around the rear of the lens allowed apertures to be adjusted manually, or turned to its ‘A’ setting, when the automation kicked in. Like the original Optima, the Reflex had its own ‘Magic Lever’, but now it was combined with the shutter release. Film speeds were set on a top-mounted dial, then the automation worked in a similar, though not exactly the same, way to the Optima.
The shutter speed and aperture began by defaulting to 1/250sec at f/22. As light levels were measured by the meter cell above the lens, the shutter remained at 1/250sec while the apertures opened steplessly until they reached f/8. After that, shutter speeds and apertures automatically combined and changed to set the correct exposure until they reached 1/30sec at f/2.8.
1961: Voigtländer Ultramatic
The Ultramatic was a masterpiece of mechanical camera engineering. Speeds and apertures could be set manually with rings around the lens. As the aperture ring was turned, pointers automatically moved towards and away from each other around the focusing scale to indicate depth of field. With the aperture ring turned to its ‘A’ setting and a shutter speed from 1-1/500sec selected, the camera measured the light through a selenium cell above the lens and set the aperture automatically. The mechanics that made that happen were complicated.
Before exposure, the aperture was open by default at its widest setting – f/2 on the 50mm Septon lens or f/2.8 on an alternative Color Skopar lens.
The leaf shutter was also open and the reflex mirror blocked light to the film. When the front-mounted shutter release was pressed, the shutter closed, the mirror swung up, the aperture closed to its automatically selected position, the shutter opened and closed again to make the exposure, the mirror swung back down and the aperture reopened to its widest setting again. This use of an instant return mirror was unusual with leaf shutters at the time.
A range of interchangeable lenses from 35mm f/3.4 to 350mm f/5.6 was available for the Ultramatic, along with the 36-82mm Voigtländer Zoomar, the world’s first commercially successful zoom lens. It all added up to making the Ultramatic one of the most desirable cameras of its age.
1961: Yamotto Emitax
In the 1950s the Japanese Yamoto Koki Kogyo company made a small range of stylish and compact 35mm cameras that looked similar but with subtle differences in their spec, some with straight viewfinders, others with coupled rangefinders, and even with hot shoes on the later models. This camera came towards the end of the company’s life and, for export purposes, it was made under different names. Other than Emitax, the camera was also known as the Palmat Automatic, Mini-Electro 35, Mansfield Skylark and Kalimat.
The lens was a 40mm Emikon, slightly wide for the 35mm format. No f-stops were marked or adjustable manually, but the maximum aperture was probably about f/4. A setting on the lens was marked with numbers 2-6, which correlated with film speeds of 10-200 ASA, as indicated by a scale on the camera back. Choosing a number and therefore setting the film speed also selected a shutter speed, starting at about 1/30sec. So, once a film speed had been selected, the shutter speed could not be altered. Pressing a large lever on the side of the body then activated the automation, fed by a large selenium meter. It’s likely that this worked by Yamotto’s own version of the old Kodak trap-needle system.
1962: Edixa Electronica
The German Wirgin company made a vast variety of camera types, typified by its Edixa range which incorporated viewfinder models, subminiatures and, most famously, SLRs, of which the Electronica was the most unusual and technically sophisticated. When it was announced at Photokina, the huge German camera fair, in 1960, it caused a sensation. But political wrangling inside the Wirgin company, meant it didn’t reach the market until 1962.
The Electronica utilised an unusual form of program automation. After setting the shutter speed, a regulator button on the back was pressed, causing a meter needle, driven by a selenium cell on the front of the body, to swing across a window in the top plate. This was rapidly followed by another needle. When the two coincided, exposure was locked and a tiny motor, driven by batteries in the base plate, began to rotate the aperture ring until it reached the appropriate setting. If the correct exposure could not be achieved in this way, then the system switched to rotating the shutter speed dial until an accurate exposure had been attained.
The camera might still be used manually today. But for the wonders of the automation to be utilised it unfortunately needed five 1.35-volt Mallory RM-1 mercury batteries no longer available.
What to pay
Agfa Optima: £15-20
Agfa Optima Reflex: £30-70
Bell & Howell Electric Eye: £15-25
Durst Automatica: £50-80
Edixa Electronica: £120-180
Paxette Electromatic: £30-50
Savoyflex Automatic: £100-150
Super Kodak Six-20: £1,500-2,000
Voigtländer Ultramatic: £50-75
Yamotto Emitax: £35-50
Related reading
- Here’s why I ditched digital for analog film – and I’m not going back
- How to get started in film photography – a beginners guide
- How to check if a film camera works
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