fast growing plants or flowers opening = 2 minutes
dark skies with stars = 20-30sec
midday sun = 20sec
cirrus clouds at sunset = 10sec
quickly moving cumulus clouds = 2-5secs
people walking 1-2secs
number of exposures needed
video clip duration in secs x video frame rate (eg. 24fps)
tricks to avoid flicker
flicker is generally caused by the camera changing the lens diaphragm between shots - even if the “same” aperture is used for each shot, small variations will cause some flicker
use the wide open aperture with a ND filter, or,
consider using a de-coupled lens, such as:
a legacy lens without electronic coupling
an “incorrectly” mounted electronic lens
set focus and aperture, then press and hold the DOF preview button while you partly dismount the lens slightly so that the aperture reading in the camera is zero
camera settings
manual mode or aperture priority is usually best for consistent images shot-to-shot
set a white balance - do NOT use auto WB, especially if shooting jpegs, although less important if shooting RAW
avoid auto ISO as cameras will generally increase ISO before slowing shutter speeds at these speeds
shoot RAW if possible
set max. shutter speed to twice the planned video frame rate (ie. for 24fps, use 1/50th sec or slower) to give a natural looking motion blur and avoid stuttered motion look of the video clip 1)
set manual focus
ensure you have plenty of battery life, especially in cold environments