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Minox AG 1 Flash Unit for Minox A/IIIs
Since 1954, the Minox A/IIIs had a synchronized flash connection. However, a flash unit had to be purchased from a third-party manufacturer. A sync cable was required.
In 1960, Minox GmbH introduced the AG 1 flash unit, a small revolution in the realm of subminiature photography. Designed as the perfect companion to the iconic Minox A camera, this compact accessory combined technical sophistication with the precision synonymous with Minox. It greatly expanded the capabilities of the Minox A.
When the device came onto the market, it was probably the smallest flash unit in the world. At the same time, it has an impressive light output (flash guide number 39 with ISO 100, AG 3B bulb). When closed, no reflector disturbs its shape, which corresponds exactly to the Minox camera. There is also no need for a cable or separate clip-on shoe. The flash unit is plugged on the camera and is immediately ready for use.
The small reflector of the Minox flash unit has one major advantage: it provides a soft light.
The Minox A and Its Era
The Minox A, first launched after World War II and produced until 1969, was already a technical marvel. Measuring just 82 x 28 x 16 mm and weighing a mere 70 grams, it was an ideal camera for discreet, portable photography. Its Complan lens (1:3.5/15 mm) and shutter adjustable from 1/2 to 1/1000 seconds offered impressive flexibility. However, until 1954, it lacked a crucial feature: a flash synchronization contact. This was later added, and by 1960, the AG 1 flash unit arrived as a tailored solution.
Overview
The AG 1 flash unit was specifically engineered for the Minox A, utilizing the AG 1 flash bulbs (introduced 1958) – the smallest of their kind. In relation to their size, these flash bulbs have a high lighting power – even compared to modern electronic flashes. With a flat glass base and a guide number of approximately 12 to 14 (in m, at ISO 100), these bulbs provided a compact yet effective light source.
The flash unit was plugged directly onto the Minox’s sync contact, eliminating the need for a cable. This was, of course, more convenient, faster, and space-saving. The design was minimalist yet functional – quintessential Minox.
Operation
Operation is straightforward: Mount the device, insert a flash bulb, extend the reflector and set the camera to a shutter speed of 1/20 second:
Caution: only trigger the flash when the reflector is extended! It also serves as a protective shield for your face against the enormous heat of the flash.
Important: The flash bulb should only be inserted shortly before the flash is triggered to prevent the battery from slowly discharging. So do not store the flash with an unused bulb for a longer time.
Kasemeier1 gives the following distance recommendations for Minox (f3.5) with AG 1 bulbs:
| film speed | distance |
|---|---|
| ISO 13…14 | 1 … 4 m |
| ISO 40 | 1.5 … 6 m |
| ISO 100 | 2 … 8 m |
| ISO 200 | 3 … 12 m |
Technical Ingenuity of the Minox AG 1
The AG bulb
The photo above shows a new and a burnt-out AG 3B (“Blue”) flash bulb. You can clearly see the flammable filaments made of metal wire on the left. On the right you can see burning residues inside and the blue plastic layer surrounding the glass bulb, which has been blown up by the heat. The two contact wires for ignition can be seen on the glass bases.
Design
Flash bulbs feature a sealed glass enclosure housing either a slender wire or a thin sheet composed of zirconium. The interior of the enclosure is filled with oxygen at a reduced pressure. Electrical connections, or electrodes, are linked to the wire or sheet, enabling the passage of electrical current. To achieve maximum miniaturization, AG (“All Glass”) bulbs connected electrodes directly through the bottom glass, dispensing with the standard base. AG bulbs manufactured by General Electric were first sold in 1958.
Safety aspects
An unused, intact AG flash bulb can be recognized by the blue dot on the glass. It indicates that the bulb is still airtight. A key factor in light bulb explosions is air infiltration through a damaged base seal. This leads to elevated internal gas pressure, and the subsequent heat-induced expansion can cause the bulb to burst. To mitigate this risk, manufacturers employ a color-changing indicator, specifically a blue cobalt spot that turns pink upon air exposure. Any bulb displaying a pink spot should be considered defective and removed from service.
Types
There were different variants of the AG flash bulb type. They differ in color temperature and amount of light:
| type | light output | lighting time | color temperature | bulb color | flash guide number |
|---|---|---|---|---|---|
| AG 1 | 7500 | ? | 4000 | clear | 26 |
| AG 1B | 5500 | ? | 5500 | blue | 22 |
| AG 3B | 7500 | 15 | 5500 | blue | 26 |
Light output: lumen seconds
Lighting time: milliseconds
Color temperature: ° Kelvin
Flash guide number: ISO 50, 1/25 s, distance in m
Note the high flash guide numbers!
Synchronisation with the camera
Unlike modern electronic flashes, which fire almost instantaneously, flash bulbs have a “warm-up” period (typically 0.020 seconds). This warm-up time means the flash must be triggered before the shutter is fully open to ensure the maximum amount of light reaches the film during the exposure. The “M” in “M sync” stands for “medium,” indicating the medium burn time of flash bulbs. M synchronization is designed to trigger the flash within a specific time window before the shutter fully opens.
The flash is fired mechanically by the shutter in the camera using M synchronization. M synchronization is a flash synchronization method designed for cameras using leaf shutters, necessary because flash bulbs require a certain amount of time to reach their peak brightness. This only works with the Minox at 1/20 s shutter speed (or longer). This value must therefore be set.
The camera shutter has a built-in contact that triggers the flash, and these contacts are timed to fire the flash before the shutter opens. This aligns the time it takes for the flash bulb to reach its full brightness with the time the shutter is open.
Minox B, escapement partially removed.
In essence, M synchronization is a technology developed to compensate for the delay in flash bulbs and ensure proper exposure in cameras with leaf shutters.
The electrical circuit
In the 1950s, flash units for flashbulbs relied on a relatively simple circuit to generate the current required to ignite the bulb. The core components were a battery, a capacitor, and a trigger mechanism. The electronic circuitry of the Minox AG 1 flash unit followed a common concept at the time. It ensures that a sufficiently strong ignition current is always available, even when the battery is running low. Thanks to Rainer for the explanations in the Blende-und-Zeit-Forum.
H: AG 1 flash bulb, S: sync contact
As long as the switch S is open, a small current flows from the battery via the resistor R and the flash bulb H to the capacitor C and charges it. The current is so small that the flash bulb is not ignited. As soon as switch S is closed, the maximum current flows from the capacitor to the flash bulb and ignites it.
Battery: The power source was typically a 15 volts high-voltage dry cell battery. This battery provides the initial charge for the capacitor.
Today, you can easily make a replacement battery yourself using button cells. To do this, take 10 LR54 button cells and a spacer to achieve the required height. The whole thing is stabilized with shrink tube or adhesive tape, see photo above. I made the spacer from an empty button cell, the poles of which I bridged with solder wire.
The following explanation of the battery in a book on Minox cameras, which was very popular at the time, shows what has also changed in the image of women in the 69 years since this flash unit was introduced:
“The capacitor has a practically unlimited service life, but the battery has to be replaced from time to time. The battery is similar to a woman’s beauty: no one can guarantee how long it will last. The advantage of the battery is that it can be replaced when it gets old and weak. In general, you should buy a new one after two years at the latest.”
Kasemeier, R. (1957): Kleine Minox – Große Bilder, Heering-Verlag, pp. 150-151
Capacitor: A 100 µF electrolytic capacitor is used to buffer the electrical energy. When the capacitor is fully charged, it holds a significant amount of energy ready to be discharged through the flashbulb.
Charging Circuit: The charging circuit consists of the resistor R connected in series with the battery and the capacitor C. This 2 kΩ resistor limits the current flow to prevent the flash bulb from being ignited by the battery. The current of I = U/R = 15V/2kΩ = 7.5 mA is not sufficient for this, but charges the capacitor quickly.
As long as an unused flash bulb is inserted, current flows from the battery to the capacitor. Without a bulb, this circuit is interrupted. The bulb should therefore only be inserted shortly before the flash is triggered to prevent the battery from slowly discharging. After the flash is triggered, the circuit inside the bulb is interrupted. A used bulb can therefore remain in the device without the battery discharging.
Trigger Circuit: The trigger circuit controls the discharge of the capacitor through the flashbulb. It involved the sync contact S, mechanically linked to the camera’s shutter mechanism. When the shutter was released, the switch closed at the right moment, completing the circuit between the capacitor and the flashbulb.
Flashbulb Ignition: When the switch closed, the stored energy in the capacitor is rapidly discharged through the flashbulb. This sudden surge of current causes the thin wires inside the bulb to heat up and ignite the combustible material with the pure oxygen inside the bulb, producing a bright flash of light.
Synchronization: To synchronize the flash with the camera’s shutter, the trigger switch was designed to close at the appropriate moment during the shutter’s travel, see above. This ensured that the flash occurred when the shutter was fully open, capturing the image on the film.
Significance for Photography
Before the AG 1 flash unit, the Minox A was limited to daylight or well-lit scenes. This unit significantly broadened its scope – from evening snapshots to indoor photography. Users appreciated the ability to push the boundaries of their Minox A, capturing moments that were previously out of reach. The compact AG 1 bulbs perfectly complemented the camera’s portable ethos. Together, the camera and flash unit could still fit into a pocket – a convenience few systems of the time could match.
A Reflection of Its Time
In 1958, flash technology was evolving. While large bayonet-base bulbs (like the Osram XO) were still common, the AG 1 bulb ushered in a new era: smaller, more efficient, and more portable. It also reflected the transition from battery-powered flashes to capacitor-driven systems. For Minox, the AG 1 underscored their innovative spirit—a company that didn’t just craft cameras but built entire photographic ecosystems.
Today, the AG 1 flash unit is a coveted collector’s item. Its condition varies – many units bear signs of use, but fully functional examples in mint condition are rare and valuable. AG 1 bulbs are still available. For analog photography enthusiasts, it’s a tangible piece of history that brings the era of subminiature cameras to life.
Conclusion
The Minox AG 1 flash unit of 1960 was more than just an accessory – it was key to unlocking the Minox A’s versatility. It embodied the engineering prowess and inventive spirit that define Minox, illuminating new possibilities in photography. Whether for enthusiasts or everyday photographers, the small but powerful device completed the Minox A experience. Holding it today evokes the pulse of an era when technology and creativity went hand in hand – a small but brilliant chapter in photographic history.
- Kasemeier, R. (1957): Kleine Minox – Große Bilder, Heering-Verlag ↩︎
