I'm often amused when taking my camera into museums and galleries when they tell me
'You can't use flash!"
for the simple reason that my camera doesn't have a built in flash. On camera flash is anathema to serious photographers for the way that it flattens subjects to cardboard cut-outs surrounded by the outline of the dark shadow the light produces. Being able to move your light source enables you to move it and sculpt the subject as you'll see from many of the flash lit images on this site. I use speedlites, the term Canon gives to flash flash units which aren't integrated into the camera.
If the flash unit isn't part of the camera then you need a way to trigger it when you press the shutter button, and over the years I've used cables, infra-red, radio transmitters and other flashes to activate them. I've set the power levels using through the lens metering from my camera, or setting them manually and tweaking them until I achieved the results I wanted. I've fired them through grids, umbrellas, soft boxes, beauty dishes and coloured gels, but there was one use of my speedlites that I'd not explored. Multi-flash, or stroboscopy.
In simple terms this is a method for firing your flash multiple times during an exposure, so that if a subject is moving that movement is frozen each time that the flash illuminates the scene. If you're familiar with the work of Eadweard Muybridge you'll have some idea of what might be achieved.
Due to Covid lockdown I'm afraid I don't have access to people to demonstrate the effect, and even if I were to set up the equipment to trigger automatically I don't have the space indoors here to model dramatic movement myself, so I resorted to some smaller objects and a table top. The trick is in deciding on the interval between flashes and the number of flashes to use; the latter being important for deciding how many times each object is captured in the final image.
Looking at these examples you may wonder why I'm sharing these on my portrait photography site, but imagine using this with a dancer in motion, or a sportsperson in action.
I can't wait to try it when lockdown is over, so if you're interested drop me a line.
So another technique added to the armoury. I couldn't resist a little photoshop work too!