I have Sunpak 622 Super Pro Handle Mount TTL Flash. Would it be compatible with a Pentax K50?
Before you attach it to your camera you must check the trigger voltage first, never use an old flash unit until you check the trigger voltage with a multimeter, most old flash units have a huge trigger voltage that will damage your camera.
Very simple to check the voltage on that Sunpak 622, turn on your volt meter and set it to about 200 volts DC, turn on your Sunpak flash and apply the RED lead to the bottom contact, apply the Black lead to the side of the hot shoe and look for the ground, usually a small metal piece on the side. Now look at the meter, if it shows a voltage of 6 volts or less then it is safe to use on your camera, if voltage is higher, say 12 volts or more, don't use it. A high trigger voltage will certainly mess up your camera in the long run. Even if it has a safe voltage of 6 volts or less, you will only be able to use that flash in Manual Mode, the newer cameras will not sync or recognize an old flash unit.
I have an old Vivitar flash unit that I can safely use on my Canon XTI because the old vivitar has a trigger voltage of 5 volts, safe for all newer digital cameras.