Light Sensitive Resistors for Switching

How about a photocell relay?

How quickly does the secondary flash need to fire?

The circuit is easy using a (little) relay for the trigger, but relays aren't very fast. Solid state would be a lot faster, but we'd need to know more detail of what was being switched.

If slow-ish is OK, come back with some typical shutter speeds, otherwise more detail of what has to be switched.

Adorama is the place I bought a slave flash for around 25.oo US. it works well and survives long enough to put somewhere and turn on for ready, they will typically sit on idle for hours and using rechargable batterys offsets the small drain while on but not used, typically a slave for fill or two to illuminate for close up is all you would need, new digital cameras are getting really sensative but I still like film for those important shots, guess I don't trust electrons as much as silver chemistry. adrorama.com
Mitch , retrired Peugeot mechanic

Any good photographic shop should be able to sell you one for around £10.

If you really want to build your own http://circuitwiringdiagram.com/2010/02/circuit-diagram-slave-flash-light-control-using-three-components-only/

I have some problems with that link...

(1) The item on the left is labeled BT1, which to me indicates a battery, and the symbol shown is that of a battery. The text talks about a solar cell, so I guess that must be what is indicated by the battery symbol, but the symbol or the label, or both, should be changed to indicate that it is a solar cell, not a battery.

(2) The inductor is a direct short across BT1. This would rapidly drain a battery, and would pull the voltage of a solar cell down to near zero, except for very rapid changes in cell voltage, which is clearly the intention. The author indicates that the inductor is 'huge'. He doesn't say whether that refers to the inductance or the physical size/weight. An inductor that large has significant weight! An appropriate capacitor in series with the photocell would provide the same function at greatly reduced weight, cost, and physical size. A resistor of the order of 10kΩ between the SCR trigger and ground would reduce false triggers, if necessary.

(3) Photocells are not known for rapid response. If you are indeed using shutter speeds below 1/100 sec, this circuit may work for objects that are not moving. For higher shutter speeds, a phototransistor with a 3V button cell would probably be better. I have NOT actually tried it...

(4) I have some problems with the text, but since it appears that English is not the first language of the author, I'll refrain from any specifics...

If you enjoy building your own stuff, try several options! Otherwise just buy them...

Thank you for your responses.

Not in any particular order:

The flash guns only require a closed switch - neither voltage nor current are required,

Shutter speeds are generally around 1/100 second or slower,

I will investigate photocell relays (not had much need to know of them previously)

visit to the local photoshop planned.

the circuit diagram shows a 68 mH choke - is this a standard value - I will answer this myself!

Tony

A photocell relay will be to slow. The triggering flash will have been and gone before the photocell relay operated. The shop bought ones are cheap, cheerful and reliable. I've fired up to 10 units from them at a time. A mixture of Metz and Bowens units totalling 4K Joules all from a tiny camera mounted flash.

It's not worth the hassle of building your own.

TonyS,

Thank you. I will pursue the camera shop route

Tony

http://www.google.ca/#hl=en&expIds=17259,26714,26781,26805&xhr=t&q=photography+%2B%22slave+trigger%22&cp=27&pf=p&sclient=psy&safe=off&aq=f&aqi=g4g-o1&aql=&oq=photography+%2B%22slave+trigger&gs_rfai=&pbx=1&fp=45594ad3fad1e662

Use a good quality photo cell as a trigger. No need to power them. The output can be given to an Op Amp. Many types of Op Amps available in the market.

The Output of the Op Amp then can be used to trigger a power transistor (for low out put, say 10 to 20 watt short distance flash, one step power transistor circuit should be enough. For higher output, two or three stages shall be needed). The output then can be given to a flash bulb (solo or set, as per your choice).

This whole thing shall cost about 200 Rs. in India. In UK however, it might cost you about 5 to 7 Pounds (or 8 to 10 Euros may be).

And for my advices there are no charges. But time should be convenient (India afternoon best, around 5 hours earlier than your afternoon).

Ashok Shukla

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A flash unit doesn't need an output.

We're talking of firing xenon tubes of may be 5 to 50K Joule (5 to 50,000 watt/seconds) with a burn duration of less than 1/60^th of a second. 10 watts would be useless.
I did tests on a Bowen Quad 1000B at full 1000J output, the burn time was 400^th of a second 400A @ 600V for a single xenon tube.

PS Don't put phone Nos. in posts

Check this site: http://www.discovercircuits.com/index.htm

What about an array of reflective mylar (or whatever)? It doesn't need electricity & can be adjusted for intensity (proximity, sq.footage & angle). Thanks Carlos