Welcome
to the photo flash-section of Johan Brouwer
problems and solutions changing from
an analogue to a digital camera
part 1: electronics
November 2002
Problem description
With my new camera [Canon Powershot S40/ 4 Mpixels] I had no separate
flash contact, implying that I could not use my electronic flash
[Metz Mecablitz 45 CT-1].
Consequences:
- 1.) Low flash output.
consequence: the maximum range was
approximately 3 meters.
- 2.) Small distance lense - flash.
consequence: red eyes.
This is caused by reflection of the flash in the retina. The
smaller the angle flash/ eye/ lense, the worse. So if possible
reduce the distance to the person and increase the distance lense
to flash, which is not possible with a built-in flash.
More problems
The easiest would have been to use
my Metz as a slave flash to counter the output problem.
However a slave flash would NOT have resolved the second problem,
red eyes, since the built-in flash would be reflected anyhow in
the eyes of the person.
Note: a slave flash trigger unit is available as an option from Metz:
(Mecalux 11, Servo-flash release for the wireless remote
triggering of additional flash units. OrderNr. 00000011 2).
In addition to all this, my Metz has an 'old' high voltage
trigger circuit. There is voltage of approx. 250 V over the
contacts!
The solutions
Apart from the Metz accessory, there is no standard
solution from the photo industry.
Note: There is a Metz "34 CS
2" digital with a built-in servo/ slave flash function, but
the output is not as high as the 45 CT-1, the beam can only be
pointed forward and last but not least it uses two
non-rechargeable batteries of 8 Euro each!
Neither the 'electronic shops' could offer any solution, so I
decided to build the high voltage flash trigger myself and put
the data on the www since I will probably not be the only one
facing this problem.
On the www I found various circuits, but I found them too
complicated: too many components, separate power supply needed,
obscure feedback in the circuitry etc. until I found the
excellent site from Samuel M.
Goldwasser (thanks!).
Only seven components needed (plus a Sunday
afternoon). I modified his concept slightly to the following:
On the output side an electrolytic cap (2.2 uF) is charged
from the flash's trigger voltage to 6.3 V. This voltage is
limited by a zener diode. When triggered, the phototransistor
discharges the capacitor into the thyristor's gate and fires the
thyristor and thus the flash. Note: the base from the
phototransistor is not connected.
Notes:
1.) Initially I used a 1 M resistance which worked fine with the
Metz. The serial resistance of the Agfa flash circuit was so high
that the 1 M resistance caused a voltage collapse and hence it
did not work. Increasing it to 10 M it worked all right for my
Agfatronic 401CBS.
2.) Previously I used a BPW 14 phototransistor that worked fine
too. The BPY 62-3 is a more modern type.
3.) For a "conventional low voltage" circuit, the 10M Ohm resistor
should be replaced by a 10k Ohm resitor. (tested, works fine)
I built it for both my Metz Mecablitz 45 CT-1 and my Agfatronic 401CBS and it works very well.
 click to enlarge |
The housing can be made very
small For a suggested "3-contact-strip prefab
print" set up: |
| From the housing, two wires
emerge: - to the section with the phototransistor, i.e. to the camera (wire to separate mounting) - to the flash unit |
 click to enlarge |
Camera with flahs unit on a tripod. Please note that the flash trigger unit is not visible (dangling from its wires, I still need to find an elegant solution for this) |
 click to enlarge |
Clearly the
phototransistor's bottom can be seen. The wires
(collector/ emittor only) are soldered on the reverse
side. Two straps fix the cable to the plastic mounting. Please
note that I deliberately blocked the built-in flash, to
avoid the red eye effect!
|
 click to enlarge |
This concept has recently be adjusted for my new camera, a Canon Powershot S3IS. I adjusted the flash power to "minimal" and positioned the photo transistor into outer bounderies of the flash light. The "main flash" is not blocked; its output being negligible to the main flash. Settings: manual 1/125, diaphragm e.g. 8, iso e.g. 100.
|
More handy tips
Another handy circuit that combines both "slave flash" as well as "connect high-voltage flash units to modern electronic cameras" can be found here.
For those of you that do not feel comfortable putting the circuitry together, possibly this commercially available item - only for sale in the USA (?) - may be interesting.
The Metz uses 6 1.5 V batteries, generating a 9 V supply
voltage. From an old printer I had a separate power supply which
gave 15 ... 18 V, too much. So I put in a 9 V voltage stabiliser:
L7809V. Low cost, and
it saves lots of batteries!
 click to enlarge Note: photo shows voltage stabiliser without insulating material, which was added later. |
The wires from the power
supply go to mounting block, from which wires are
soldered to the L7809V. I fixed the L7809V to a piece of metal (aluminium, not ideal, copper would have been better) to allow its heat to be dissipated. |
