NB: This series of posts will convey my understanding of flash photography. While I hope it serves a useful purpose, I by no means describe this series as a be-all, end-all resource on flash photography. As ever, if you feel I have made a factual error, please correct me.
This week, I’ve decided to try and show three flash modes which I use now and then: high speed sync, stroboscopic, and trailing curtain sync. Brief summaries of each will follow pairs of pictures showing the difference the flash mode makes to the picture.
High speed sync allows syncing with shutter speeds above the nominal flash speed, but sacrifices a lot of flash power in the process; it’s not uncommon for me to drop to 1/64th power or less, especially against strong backlighting.
Stroboscopic mode allows control over the frequency and number of flashes, giving a similar effect to the strobe light on a dance floor (unless I’m imaging the existence of such a thing). This is quite handy for motion studies and similar applications. Like high speed sync, you lose flash power (the samples here were taken at 1/64 power). However, due to the cumulative effect of having multiple flashes, I find the exposure is a bit difficult to get right first time. This situation is exacerbated by forgetting how to use a flash meter for multiple flashes… It always pays to read the manual thoroughly!
Trailing curtain sync is applicable (and more noticeable) in long exposures. Rather than synchronising the flash with the opening of the first of the two shutter curtains, the flash is synchronised with the closing of the second shutter curtain. This freezes the object at the end of its travel; the motion blur from a slow shutter speed follows the subject, rather than leading the subject. Overall, this lends a more natural appearance, and minimises ghosting. Ghosting occurs when a subject is stationary long enough to be exposed by available light, such as at the end of its travel. When I’m doing anything with movement and flash, this is the method I usually use.