mrnews

I am thinking of doing almost the same thing with my D40 and an old Vivitar 253 flash. E-mailed Nikon on this, and they cited the 250 volt maximum figure. Another website shows that someone who tested a Model 253 found the trigger voltage at 200v. I have e-mailed Vivitar requesting the trigger voltage spec on this model, but will be suprised if they actually provide any data. Preparing to borrow a neighbor's voltage meter and test the unit myself...

Yes it is true that you might damage the camera electronics and/or the flash with high (or negative) voltage. Thus it's worthwhile to investigate thoroughly before using a non-OEM speedlight.