The Sunpak 522 is a professional studio flash. It feature the most accurate and reliable metering I could imagine when used in auto mode. The weakness is the poor ergonomics.
The Sunpak 522 is also known as Sunpak 3600 (I think it was the European version)
I purchased the Sunpak 522 after being disappointed by the Braun BVC 420. When I received it I noticed that I did not realized that the Sunpak 522 was so huge and unbalanced compared to the Braun hammerhead flashguns. The reason is in the battery location: 6 AA batteries located in the head for the Sunpak 522 and 4 AA batteries located on the hand-grip of the Braun. So the gravity center is to high to be well balanced on the Sunpak 522.
My model was using a 6 cells battery will most of Sunpak 522 are available with a 6 AA batterie holder. If you are intereted in purchasing this model on the after market you should be carefull on this point: the 6 cells batteries was to old (leaks) and I had to rebuild it using and soldering 6 AA NiMh batteries in the old battery case. This operation is not easy.
The Sunpak 522 can also be powered by external power supply or by external high power battery pack.
My model came with a Canon dedicated remote light sensor: RS CA-5
This sensor has a battery compartement. Maybe this battery was used when using this flash in Canon TTL dedicated mode but in normal (AUTO) mode this battery is useless. So I removed it. This sensor features the same settings as the flash himself except an optical setting for the front lens of the ligh sensor. There are 2 settings : N (Narrow) and T (Tele) to adjust the metering area. The light sensor of the remote sensor is the bigger I have ever seen:
This flash is very versatile thanks to it wide setting scale starting from F 2.0 when iso is set on 100 (to be compared to F4.0 for the excellent Braun bvc 370) going to F64 ! by increments of 1/3 F/stop. So you have no limits.
For use in manual mode, power reductions availables are Full power, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64 but there are 2 intermediate more settings bettween each of the previous listed values! So the power reduction mecanism is very sofisticated.
The next picture shows the size of the Sunpak 522 mounted on the Sony A700 DSLR. This is a very heavy equipment.
The ergonomics of the Sunpak 522 is the main weakness (with the weigh). The head does not rotate smoothly at all. You are afraid to break it each time ou turn the head while it is very robust!
An other weakness compared to Braun BVC hammerhead : it is very unstable due to the massive screw thumb wheel under the bracket. See next picture:
Concerning the metering when used in auto mode, as I said it is 100% accurate and 100% reliable using or not the remote sensor. It is true in direct light or in indirect light (bounced). It is incredible to figure out how this analogical electronics can be more accurate than modern numeric one particularly when used bounced.
I measured 5.6 volts applied on the hotshoe pins with the remote sensor. So it is safe with the shoe of the Sony DSLR which is limited to 6V.
(The PC-Sync socket of the Sony Alpha 700 accept 400 volts)