Canon EOS Camera Non Canon Non Dedicated Flash
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.
Any trigger circuits which requires more than 6 volts could possibly damage the X-Sync contact of the camera, the shutter units or connecting wire. Damage might not be immediate and may result over a period of time. Furthermore the high voltage passing through the Camera connecting wire might also generate electro magnetic "noise" resulting in unwanted adverse effects on the camera. Errors can occur with metering, shutter speed, aperture size etc depending on the camera models and which part of the circuit layout is affected.
To test a Flash trigger circuit voltage level, you just need a simple voltmeter. This can be purchased at any Radio Shack stores. Just connect the positive lead to the positive of the PC contact of the sync cord and the negative lead to the ground of the PC sync cord. For those Hot Shoe mounted flash units, the positive lead should be connected to the middle of the shoe mount while the negative should be connected to the ground contact on the side of the lock nut. All Multimeters or Voltmeters have different setting for you to test the DC voltages. If you do not know the voltage, then it is best to start testing in the high range downwards.
You can actually fire a Studio Flash unit safely without a Sync cord. To do so, just use a Speedlite 420EZ or 430EZ at 1/32 power setting under manual flash mode. Make sure the optical slave trigger is turned on before firing. What you are actually doing is utilizing the bounce features of the Speedlite 420EZ or 430EZ to divert the flash light to the optical slave trigger. On the other hand, you can use slave triggers which are linked by radio signals to fire the Studio flash. These radio transmitters and receivers, which are connected to the Camera's PC contact and the Flash power packs, are manufactured by companies like Lindahl and Quantum Instruments.
If the Studio flash does not work with the Canon EOS Camera, you have to check on 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. The flash units polarities might be reversed. This can occur because of a diode which is connected to the camera X-Sync point to protect the Camera internal flash unit. To get by this problem, reverse the polarities of the Sync cord.
(3) If the above two solution still do not work, then the best way is to use the methods described above to fire studio flash safely.
