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I use a Sony A7S. Recently, I bought two old Panasonic PE-20s'.
I've used it a couple times through the hotshoe without fail but recently I read up on how high flash trigger voltages can fry your camera.
I'm a little worried now. I think the Panasonic's trigger voltage is 6.2 and my Sony A7s is rated for a max of 6v.
Should I be worried?
In general, be worried.
Specifically, read on ...
Added: Just found the A7S compatible FA-CS1M Sony adaptor, presumably with high voltage protection (as their prior models have).
ebay
B&H $39
legion
Some cameras are more easily damaged by excess flash input voltages and reading users comments only there is some suggestion that Sony cameras may be more sensitive to voltage damage than others. This is largely a matter of manufacturing philosophy on the manufacturer's part - Sony are perfectly capable of making the flash input as voltage tolerant as they wish.
You can measure the flash's terminal voltage with a DMM (digital multimeter). Set the meter to a suitable volts range - probably 20V. Measure the voltage between every combination of 2 contacts. (I'm not conversant with the 7S hotshoe but eg a 4 contact show has 3+2+1 = 6 combinations. )Polarity doesn't matter. Once you find the 2 contacts with highest voltage between them measure again with the meter on a higher voltage range. eg if it read about 6V on the 20V range make sure it still reads 6V on the 200V range. (Modern DMMs tend to have constant input resistance on all voltage ranges but some load the circuit less on higher voltage ranges).
So measure and report back. 'Inquiring minds want to know'.
If a camera spec said it was rated at 6V max and actual was 7 or 8V I would expect it to still be safe BUT I would alos be nervous and not trust it.
If the voltage is slightly above spec- say 7.5V when the camera spec says 5V max, you could try loading the flash terminal down with a resistor or zener diode. In some cases a flash with 7.5V say open circuit could be loaded down to maybe 1V to 2V before it triggered, so loading it to 5V may be acceptable. There is a small chance of this not triggering the flash bur causing some secondary effect but this is unlikely.
Some flashes use over 20 V on the output. Some mention 24V max. And older flashes can have several hundred volts on the trigger contacts.
Long ago I damaged a digital camera by connecting a flash that was allegedly compatible with the camera brand - but in fact wasn't. So - it can happen.
It is possible to buy adaptors that reduced voltage - at suitably excessive process, and it would be trivially easy to design an adaptor circuit that does this at low cost. How to mechanically connect the camera-interface-flash is harder than designing an electrical interface.
Checking trigger voltage step by step how-to
User discussion nothing definitive, but may be useful.
@Inkista added an answer with a useful Sony reference but then deleted the answer - I don't know why - here is the reference that Inkista provided. Sam knows this but it will be of value to others . Amongst other things it says.
WARNING: Be cautious when using third-party flash accessories with your a (alpha) camera. An external flash or studio-type strobe may not operate correctly if the trigger voltage of the flash/strobe is higher than 6 Volts. In addition, using an external flash or studio-type strobe with a trigger voltage higher than 6 Volts and an accessory shoe adapter without a built-in protection circuit for high voltage can damage the camera. Damage to the camera resulting from the use of a third-party accessory is not covered under the Sony® limited warranty.
To attach a third-party flash that conforms to the ISO 518 standard, use the ADP-AMA hot shoe adapter. Using the ADP-AMA shoe adapter, it is also possible to use a Pocket Wizard® remote flash.
In addition, the Sony FA-ST1AM accessory provides a PC Sync (remote flash) terminal helpful for wired triggering of off-camera lighting systems with many DSLR and SLT camera models. It has a built-in protection circuit and slides onto the accessory shoe of the camera, while the external flash/strobe is connected to the FA-ST1AM using a standard PC-type sync cable. The external flash/strobe itself does not mount to the camera - this allows flexibility for using the flash or strobe in any off-camera position.
IMPORTANT: The FA-ST1AM is not necessary for cameras that have a built-in remote flash terminal.
Also note this Sony warning re using remote adapters
Sony also made (obsolete?) an adaptor for Alpha cameras with high voltage protection. Rather dear for what it does (IMHO). FA-ST1AM images with links
Interesting more for what it does than direct use here
http://www.bhphotovideo.com/c/product/521345-REG/Sony_FA_ST1AM_FA_ST1AM_Sync_Terminal_Adapter.html
The components for an over voltage immune trigger interface cost under $US1. Mounting and interfacing them is the challenge.
