Old-timers like me will remember the days when none of these helpful accessories existed. Unless you could figure out a solution on your own, you were, well, on your own.
Basic mirror extenders for screw-in handlebar mirrors have been around for a while, but now it’s good to know that there are many other types available that can even fit bolt-on mirrors which are mounted on a fairing.
Note, however, that depending on your physical dimensions and the motorcycle, you probably won’t go from no rearward visibility at all to full visibility. A good example of that is these SW-Motech mirror extenders mounted on the F 800 S.
But at least I have some visibility to the rear; I had absolutely zero before.
These don’t come cheap, however. The going price for this type of extender for various motorcycles is $83.95 the pair. But since you couldn’t make a set that looks so “OE” unless you owned a fully-stocked machine shop, you don’t have much of a choice.