<p>Speaking of optical slaves for Vivitar flashes, I have been using Sonia brand units I bought from FlashZebra.com several years ago. They are made specifically for Vivitar flashes including the 283 and 285. They plug into the sync cable port on the side of the flash instead of the hot shoe. They are small and relatively inexpensive at about $12 apiece and seem pretty rugged. I have been using them off and on for several years in combination with radio triggered flashes or as a supplement to the small on-camera flash on my Fuji X-20 (set to manual flash) and have had no problems with them.</p>