The Sunpak 28SR Thyrister flash is both powerful and versatile. It has two auto ranges as well as manual power settings from full to 1/32 strength.
If you leave the attached short PC connecting cord bedded in it’s groove it has a hotshoe foot connection to sync with the camera. As soon as you remove the cord from the groove the hotshoe connection is disconnected (to prevent possible shorts through the foot if the camera’s accessory shoe is all metal).
I really like the accessory foot can be rotated from facing one side through in-line with the body to facing the other side. Combined with the flash head being able to rotate through 180º and there are a lot of combinations. You would probably decide which combination of foot direction and reflector angle works best for you and stay with it, but you could take advantage of reflective walls and ceilings for varied flash results when the possibility presents itself.
The flash takes four AA-size batteries in a captive lid battery compartment. It took some playing with the battery contacts to get the flash to power up. There was evidence of battery leakage, so a battle was anticipated.
The on/off switch seems a trifle vague too. As soon as the on/off switch decided to work a large auto signal green light turns on. Some time later the ready/test light will glow orange. Pressing the ready/test button well down into the body will fire the flash. I gather—if the M/A white/A green switch is in one of the “A’s”— if the green auto signal stays on you have successfully illuminated the subject. While on the subject of Auto ranges if you have the ASA setting at 400 the A-white range is clearly shown from 2.3 to 17 feet at f/11. Switching to the A-green setting the f/stop is now f/5.6 and the range is from 4.6 feet to 33 feet.
There is a cover located under the auto signal light that might be a power input for an AC power supply or possibly an accessory battery supply—but the cover is really firmly bedded into the flash body. Rather than shear it open and then have to glue it back I am just going to leave it alone.
On the manual setting as you change the power setting from full to 1/32 the feet scale slides down. At full power at ASA 400 the closest you could shoot at f/32 is 6 feet. Then the closest distance falls at the reduced power output so you get 4 feet at ½ power, 3 feet at ¼ power, 2 feet at ⅛ power, 2 feet at f/22 at 1/16 power and finally 2 feet at f/16 at 1/32 power.
At the other end of the range at full power you reach out 66 feet at f2.8 at ASA 400.
The hotshoe is very, very plain. It has a single blade style contact balanced with metal contacts for the accessory shoe on both sides of the foot. The sync voltage on this flash's hotshoe contacts is 170 VDC. The flash with batteries installed weighs close to a pound.
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