You can build this DSLR Camera old Flash Adapter for a few dollars and still use your old trusty camera flashes on your new gear. Looks like a nice simple and robust circuit.

"This instructable shows you how to make a really easy and simple circuit, that protects your new camera from high trigger voltages in old flashes. It is completely safe and will not damage the cameras circuits! It is better than those slave adapters that "look" for a flash, and then quickly activate the flash, since those adapters can be set off by other cameras. If you’re at a party, that can be quite annoying.

what you need:

- general soldering equiptment
- a sense of electronics
- an Optocoupler with triac output (i.e. MOC3062)
- 2 capacitors ( 10 µF )
- 3 resistors ( 500, 1M, 30…80 ohms)
- a casing (optional, I got mine on ebay)
- a battery"