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05-16-2012, 01:13 PM   #1
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K-r internal flash trigger voltage limit

I just ordered a an old Vivitar Thyristor 3500 flash unit to help me with macro photography. It has just come to my attention that some old flash units can damage modern SLRs...

I have seen the trigger voltage on the vivitar reported to be anywhere between 7-9 volts. What is the official limit for the my k-r? Has anyone ever actually damaged the flash trigger and it it an expensive fix?

05-16-2012, 03:33 PM   #2
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Here is a link to some reported voltages.

I have seen posts that say 24 volts is OK for Pentax but I tend to be conservative and go with 12 volts. Some flashes go well over 100 volts and those are the ones you need to stay clear of. The Vivitar 3500 is listed at 6v and also at 9.1 so some variability in individual flashes or testing method.

Yes, over voltage can damage the camera. No idea what the cost to repair would be but not cheap.

Do a search for "how to test flash voltage" and you will find ways to test your flash.
05-16-2012, 04:55 PM   #3
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If the flash has a trigger voltage of under 12v, you should be ok. Otherwise, I wouldn't chance it.
05-17-2012, 05:45 AM   #4
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If it's too high, you can add a Wein safesync (google it) or similar. I seem to recall that the Cactus triggers also have a protection circuit.

PS There is a user (I always forget the name) here who has used a 100V-or-so flash on a Pentax dSLR camera (not K-x).

05-17-2012, 08:42 AM   #5
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Pentax have said they are conform to the standard and the standard uses 24 volt.

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