Check the listing for details. Wein HSD Digital Optical Slave for electronic flash. Condition: Used. Listed at 50.00 USD. This listing is for a used Wein HSD Optical Slave. It attaches to the foot of your electronic flash and fires it when it senses the light from another flash. The D in the name stands for digital. Digital slaves have circuitry that is designed to ignore the pre-flashes used by many digital cameras to help set flash exposure, and will only fire with the main flash that fires during the exposure. This will allow the photographer to use older, or simpler electronic flashes which lack an S2 mode with a camera that uses pre-flash. I have tested it with Camtraptions F1 and Z1, as well as Flashpoint Zoom Li-ON R2, (basically a rebranded Godox V860 sold by Adorama), and it works perfectly with all of them. Please note, it will NOT trigger a modern Nikon system flash.