Unomat B24

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Unomat B24 was a family of popular electronic flashes made by West German company Unomat GmbH & Co. KG from 1980s to 2000s.


The family included initially three models:

  • B24 - basic manual model
  • B24 Auto - automatic exposure control
  • B24 TAC - thyristor exposure control

In the later period, two new flashes were added:

  • B24 Auto Servo - B24 Auto with built-in photocell
  • B24 TAC Servo - B24 TAC with built-in photocell


The B24 is a very compact unit powered by two AA (R6) size cells, with guide number of 24 m for 100 ISO speed. The flash head can be rotated both vertically (from 0 to 90 deg. upwards) and horizontally (180 deg. to the right and 150 deg. to the left) - a very unusual feature for such a compact flash. A hot shoe is provided for flash sync and a detachable PC cord can be connected by a standard micro jack socket at the body side.
All B24 models were also supplied with a wide angle diffuser, as well as with three coloured plastic filters (blue, green and red), which can be mounted at the front of the flash head.
Except of the basic B24 variant, offering full power flashes only, the B24 Auto and B24 TAC are equipped with automatic exposure control. Two automatic settings are available, for distances up to 4.3 m and 8.5 m (apertures 1:5.6 and 1:2.8 for 100 ISO respectively). The difference between Auto and TAC models is in the automatic circuit type - the TAC uses a thyristor circuit, saving capacitor energy not consumed for a proper exposure, thus allowing shorter recycling times and longer battery life. The automatic models are also equipped with auto check feature, confirming correct exposure.
It should be also noted that B24 flashes deliver high trigger voltage (in excess of 70 V)[1] and may not be safe for modern electronic cameras.

As far as the basic B24 is an excellent, robust and reliable flash, there's however a certain problem with automatic models. The sensor controlling exposure is placed at the front of the flash body, under a clear plastic dome - a generally unusual feature, but common for many automatic Unomat flashes. Even if the measuring angle is given as 15 degrees by the user's manual, such an exposed sensor catches a lot of stray light from beyond that angle. This design flaw results in drastically underexposed pictures when the flash is bounced from a wall or a ceiling, or when the wide angle diffuser or coloured filters are used, as the sensor is fooled by bright light coming from a side (reflecting surface or a lower edge of the diffuser or filter), outside of its intended measuring angle. To avoid such a problem, the sensor has at least to be shaded with a hand, or have some kind of a shroud added. Automatic exposure is, on the other hand, correct with direct illumination without the diffuser or filters, and there are - of course - absolutely no problems in the manual mode.


  • Guide number: 24 m / 80 ft
  • Flash energy: 36 Ws
  • Flash duration, manual: 1/1000 s
  • Flash duration, automatic: 1/1000 - 1/25 000 s
  • Colour temperature: 5600 K
  • Angle of illumination: 60x45 deg.
  • Flash head rotation vertically: 0 to +90 deg.
  • Flash head rotation horizontally: -150 to + 180 deg.
  • Auto stops: 2 (Auto and TAC models only)
  • Power source: 2x AA
  • Charging time, manual and Auto: 8 s
  • Charging time, TAC: 0.4 - 8 s
  • Battery life (manual, Auto): 200 flashes
  • Battery life (TAC): 200 - 2000 flashes
  • Dimensions: 95x65x40 mm (without mounting foot)
  • Weight: 400 g (without batteries)


  1. Value measured by camera-wiki editor Grzesio


  • Unomat B24 / B24 Auto / B24 TAC instruction manual.