I have an OLD Sunpak Canon dedicated flash and I want to use it on my 'new' Sony DSC-D770 digicam. is this possible? the flash has three contacts on the bottom, but the hotshoe on the digicam only has the center contact. The Sunpak is a good flash with a guide number of 160. If I can't use this, what flash should I purchase? I need a minimum guide number of 120. thanks.