Before deciding to use Non canon non dedicated flashes with Canon EOS cameras, you will need to be aware of its trigger voltage. Canon Speedlites flashes uses no more than 6 volts in their trigger circuits. As such you have to ensure that the non canon Flashes should also comply within this tolerance. The Canon EOS cameras like the EOS-1,A2/A2E,10s,630,Elan,RT and Rebel are all designed to operate with no more than 6 volts passing through their trigger circuits.

Those triggers which use more than 6 volts can damage the electrical circuitry of the camera. The connecting wires, the X-Sync contact point and the shutters are most prone to damages. The damage might not be obvious but will happen gradually over time. Beside from the likelihood of circuitry damages, electro magnetic noises generated by the high voltages will cause interference with the Camera operation. The metering system, aperture settings and shutter speed are just some of the possible effects of electro-magnetic noise on the circuit of the camera. Which function will be affected will depend ultimately on the circuits which is interfered with by the electromagnetic noise.

Testing the voltages of the flash triggering circuit is a simple task. Just use a voltmeter which is available at any Radio Shack stores. Connect the positive lead to the positive point of Sync Cord. The Negative lead should be connected to the ground of the Sync cord. With shoe mounted flash, just connect the positive lead to the center point of the mount. The negative lead has to be connected to the grounding point of the camera located at the side of the lock nut. Voltmeters have different setting which you can use. If you are unaware of the voltage of the Flash unit, just use the highest setting on the voltmeter than work your way downwards.

To fire a Studio flash safely without a sync cord, use a Speedlite 420EZ or 430EZ with 1/32 power under manual flash mode. Ensure that the flash’s optical slave trigger is activated before firing. You are actually using the bounce feature of the Speedlite 420EZ or 430EZ to direct the light to optical slave trigger. Alternatively, you can use radio slave triggers to fire the studio flash. Companies like Lindahl and Quantum Instruments sell radio transmitters that connect to the PC contact of the camera and a receiver to connect to studio flash power pack.

If the Studio Flash is not firing through the EOS Camera, you should check the following listed below:

(1) That the third party PC socket adapter do not have a metal shoes. This will result in a short circuit in the trigger circuit. The remedy is use Canon PC socket adapter which is made from plastic.

2. Make sure that the flash units polarities are in the correct order with the X-Sync of the camera contact point. The reversed polarities are normally caused by a diode which is coupled to the camera’s X-Sync contact for the protection of the camera internal flash. To correct this problem, simply reverse the polarity of the Sync Cord.

3. If after having tired these two suggested solution and the Flash still wont fire, then just adopt the method described above to fire the Flash without the use of the Sync cord.