The flash and multflash commands take the length of the preflash in the place where the exposure-time would go for run et al. The integration is effectively the length of the preflash, and the shutter is not opened.
flash [<camera>] <time> ["<title>"]
multflash [<camera>] <n-obs> <time> ["<title>"]where time is the length of preflash for one cycle in seconds and n-obs is the number of cycles in multflash. The title-string must be enclosed in double quotes. The default title is "Preflash only".
The shortest-possible preflash time is one millisecond. The longest preflash allowed is 7.5 seconds. Typical flash times are less than one second.
All cameras have a default duration of preflash that is applied to all observations. The flash and multflash commands override this for one observation or one series of observations respectively. After flash or multflash completes, the next observation goes back to the default preflash.
At present, none of ING's CCD cameras use a preflash in normal operation. The default preflash is always zero seconds.