The SU-4 is a small gadget with a powerful punch. More than just a simple slave unit, this SU-4 is a wireless remote TTL flash control. A relatively inexpensive unit that takes on the duties of a fully armed studio lightning system. Not only it is capable of receiving the signal to fire, but also the signal on when to stop. Effective up to 23 feet (in AUTO) from the triggering primary light source (131 feet in MANUAL mode), rotates 120 degrees, mounts on any mini tripod and "Look Ma, TTL with no wires!".
It even has a beep to audibly alert if it is going to work or not (for those with good hearing). At only 2 oz. it can be carried anywhere. Street price ~ USD75 brand new.
I just unpacked, got a mini tripod for one SU-4, mounted a wide angle on the camera on another tripod and bang away on Konica Centuria 200! These pictures below are the first trials!
another SB-28 mounted on the camera.
I can't wait to have the time to play with the two SU-4 I purchased, each with an SB-28 mounted and triggered with a SB-25 I still have around.
The SU-4 is powered by the batteries on the flash. So don't leave the flash mounted on it beyond your session.
It works perfectly on Matrix Balanced Fill Flash with the SB-28 as demonstrated above, with the SB-25 as I tested later, and with the SB-27, SB-26, SB-25, SB-24, SB-23, SB-22s, SB-22, SB-21B, SB-20, SB-16B and SB-15 speedlights according to the manual.
The not-recommended-for-interiors 3D Multi-Sensor Balanced Fill Flash mode asks for pre flashes of the main flash and these may trigger the SU-4 with secondary flash before it should.
For exteriors, in the above mentioned mode, to avoid pre triggering the secondary flash with pre flashes from the main one, just tilt or rotate the head of the main flash.
It also works triggered by any Nikon camera's built-in flash.
A recommended purchase.
Of course you don't need it -to some extent- if you own the SB-26, SB-50DX, SB-80DX or SB-30, because these speedlights have a slave function.
Have a great time