Welcome to Nikonians! Here is a link that has flash triggering voltage listed: http://www.botzilla.com/photo/strobeVolts.html Unfortunatly the Vivitar 225 is not listed, though the other models with a similar vintage exceed the safe triggering voltage by a wide margin. You should verify the triggering voltage with a volt meter and or use a Wein SafeSync: http://www.adorama.com/WNSSHSHS.html?kbid=64628&searchinfo=Wein+SafeSync to be safe. Call it cheap insurance. Of course you will be limited to using the camera set in Manual exposure mode with the Flash in (non-TTL) Auto flash mode or Manual flash mode. Good Luck and Enjoy your Nikons!