Yashica Twin Lens Reflex Guide - Focal Press January 1964
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FLASH PHOTOGRAPHY
Flash is an efficient light source where no or insufficient daylight is available, such as at night, indoors, etc. In the
flashlight you carry your own private "sun" with which you can illuminate your subject or scene at any time and place.
THE FLASH BULB is similar to a small electric bulb. However, when current passes through it, it lights up in an intense
flash lasting usually about¼0 to 1/60 sec. Each bulb will flash only once and has to be discarded afterwards.
The flash bulb is inserted in a flash gun and the current of the battery fires the bulb, while a reflector fixed behind the bulb
makes sure that all the light is directed towards the subject. Most flash guns incorporate a capacitor unit which increases
the reliability of firing, even when the battery is nearly exhausted. The shutter speed, provided it is slower than 1/50 sec.,
has no effect on exposure, since the flash is shorter than the exposure time.
Most flash bulbs are available with a clear glass bulb (for black-and-white and negative colour film and for type F reversal
colour film) or with a blue-tinted bulb (for daylight type reversal colour films). The blue bulbs can also be used for fill-in
lighting by daylight with any type of colour film.
ELECTRONIC FLASH UNITS utilize the discharge of a high-tension capacitor through a flash tube. The power is
derived from an accumulator or battery (there are also models working from the mains electricity supply). The electronic
flash outfit is rather bigger and heavier than the flash bulb outfit. Its light output is about equal to that of a small flash bulb
and its initial cost is higher than that of a battery-capacitor gun. On the other hand, anything from 10,000 to 25,000 flashes
are obtained from one tube. The flash duration is extremely short (1/700 to½000 sec.) and will arrest the fastest
movements. The cost of an individual exposure is negligible.
Electronic flash is suitable for black-and-white and negative colour film and also for daylight type, reversal colour films. It
can also be used for fill-in lighting by daylight.
How to use Flash
The Yashica reflex camera shutters (except A models) are internally synchronized for use with flash bulbs and electronic
flash. The cable from the flash gun is plugged into the flash socket of the camera. On releasing the shutter, an electric
circuit is automatically closed through the flash socket, setting off the flash at this moment.
The shutter of the Yashica A models have a nonadjustable flash contact which has the characteristics of the X-
synchronization described below. On all other shutters the synchronizing lever can be set to X or M.
WITH THE SYNCHRONIZING LEVER SET TO X the shutter closes the flash circuit at the moment when the blades are
fully open. Therefore, electronic flash is synchronized at any shutter speed to 1/300 or 1/500 sec. This setting may also be
used with flash bulbs with short firing delay (i.e. bulbs which require only 4-6 milliseconds - thousands of a second) to
reach the peak of their light output with the shutter set to 1/60 sec. With other bulbs, the fastest usable speed is 1/30 sec.
WITH THE SYNCHRONIZING LEVER SET TO M the shutter closes the flash circuit 16-18 milliseconds before the
shutter blades open to allow for the firing delay of most average flash bulbs. This setting is suitable for normal flash bulbs
at all speeds up to 1/300 or 1/500 sec. The M-setting will not synchronize electronic flash or short-delay bulbs.
Exposure Guide Numbers
There is a convenient way of working out exposures with flash and this is by means of a guide number. When you buy
flash bulbs you will always find the guide number for any speed of film printed on the packet.
To find the correct aperture to use, divide the guide number by the distance between the flash and the subject. For
instance, Suppose You find that the guide number of the bulb with he film in use is 160. If you then want to take a
photograph tat a distance of 10 ft. from the subject, divide 160 by 10 = 16. Therefore, the correct aperture to use is f 16.
Alternatively, if you want to use an aperture of f8 for any reason, then the correct flash distance is 160 / 8 = 20. So the
flash must be 20 ft. from the subject.
