First you should read the How to buy a low cost flash article.
Then there are 3 ways to use the flash with your DSLR:
- connected to the DSLR shoe or via a hotshoe adapter
- connected to the PC-Sync socket of your DSLR if any
- wireless connected (optical or radio).
Only the 2 first are in the scope of this article. The 3rd is completely safe.
If you plan to connect the flash to the shoe of the camera then read your camera user manual for the maximun input voltage that can be applied on the shoe. It may be different and lower than the voltage accepted on the PC-Sync socket if any.
On my Sony Alpha 700, the maximum voltage accepted on the pin of the shoe is 6 volts (not to exceed) while it is 400 volts (not to exceed) on the PC-Sync port.
Then it is very simple to measure the input voltage:
On this sample, I have a hotshoe (not voltage save i.e. no internal circuitry) mounted on an old Braun 340 flash.
Notice the 2 pins (sync & ground) on the rear of the Minolta hotshoe adapter. The missing pins would correspond to TTL OK and flash OK signal.
This is where to measure the voltage.
Then set your multimeter to high voltage range (continuous) and power on the flash. When the flash ready led is OK, the multimeter will show the voltage.
Change the multimeter range for a more accurate measurement.
Here this flash (Braun 340) will apply 3.55 volts on the shoe of the camera.
If you have got an ISO shoe (not a Minolta one like on these pictures) the method is the same, but between central plot and side of the shoe.
If your flash do not have a shoe (hammer head) or you plan to connect the flash with a PC-sync cord, you can use the same method with a hot shoe adapter (not a voltage safe one) just for the measurement:
Then you will know the voltage that will be be applied to your PC-sync port.
