I have just been trawling thru KEH. When they have the promotions like 20% off are the bodies generally snatched up before you get there? Like the 500CMs? Also re: the 503CX, it is TTL flash as I know does it take a battery, or else how does the TTL flash work then?
I have a RB67 but it is proving a bit large for overseas. Unless I go to my hotel and take it out for just that few hours.
The batteries in the flash control everything: the sensor in the camera tells the flash unit how much light has been received through the lens. That, along with the ISO setting, is used by the flash unit to determine when to quench the light.
There is a connecting cord to use and I can't remember the name hold on I will try to find out and be back. I myself never use it so I am not that familiar.
The TTL uses flash equipment that measures the light reflected off the film to determine the exposure. Follow the manual and use the correct flash equipment by Metz and other companies with the proper flash cords. I do not use the TTL when I use the Nikon SB 800.