Canon 600EXII-RT Instruction Manual page 43

Calculating the Shutter Speed
To ensure that the shutter stays open until the end of the continuous
flashes for stroboscopic flash, set the camera with a shutter speed
calculated with the following equation.
Number of flashes
For example, if the number of flashes is set to 10 (times) and flash
frequency to 5 (Hz), set the shutter speed to 2 sec. or longer.
To avoid degrading and damaging the flash head due to overheating, set
repeated shooting with stroboscopic flash to 30 times or less. After
shooting 30 times, allow a rest time of at least 10 min.
If you shoot repeatedly more than 30 times, the safety function may
activate and restrict flash firing. If this happens, allow a rest time of at
least 40 min.
When performing stroboscopic flash, combining a highly reflective
subject with a dark background is most effective.
Using a tripod, remote switch, and Compact Battery Pack CP-E4N (sold
separately/p.123) is recommended.
Neither 1/1 power nor 1/2 power flash can be set.
You can also perform stroboscopic flash even when the camera's
shooting mode is set to <bulb(B)> (bulb shooting).
When the number of flashes is displayed as "----", flashes are fired
continuously until the shutter closes or the charge runs out. The
maximum number of continuous flashes is shown in the table on the next
page.
High-speed sync (p.31) cannot be set during stroboscopic flash.
÷
Flash frequency = Shutter speed
?: Stroboscopic FlashN
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