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In providing the
information below, we're assuming that the reader is already familiar
with the fundamental techniques of high-speed flash photography. For more information, see this pdf document: "High-Speed
Flash Photography for Amateur Photographers."
For an activity-based tutorial, see the Activities
section of HiViz. For information on using still digital and video
cameras, see the Camera
section.
Materials
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Camera with manual
focus, aperture, and shutter speed settings
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Flash unit
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Photogate trigger
-
Synchronizing
delay unit
-
Funnel with stopcock to control release of drops
Setup
and Photography
Set up the
equipment so that the funnel's mouth is above the
photogate beam. Thus, drops released from the funnel will
break the beam as they pass. Direct the flash unit toward the
location where the splash will occur, and position the camera as close as possible to that same location.
The camera needs to be close, since the splashes are small.
Use close up attachments (lens or extension tubes), if available, in
order to enlarge the image.
Connect
the photogate to the input of the delay unit and the flash unit to the
output of the delay unit. This allows one to adjust the amount
of time between the drop's breaking the photogate beam and the flash
discharging. For falls of half a meter or less, a time delay of
up to about half a second is needed.
Place
a ruler or other object in the plane where
the drop will fall to create a splash. Focus the camera on
that object. Set the camera on its bulb setting and adjust
the lens aperture. Turn the room
lights off and open the camera shutter. Let a drop fall and make a splash. When the flash fires,
the drop or splash will be caught on film. Close the
shutter and turn the room lights on.
Try
changing the delay to capture the splash in different stages.
Also try making the delay very small in order to examine the drop as
it breaks off from the funnel.
Splashes
offer a particular photographic challenge if one is to obtain good
results. The splashes are small, and one generally needs to use
close up attachments to magnify the image on the film. In order
to have sufficient depth-of-field under these conditions, the smallest
possible aperture is needed. In order to maintain sufficient
exposure, one has several options: 1) use faster film, 2) place
the flash unit closer, 3) intensify the light from the flash using a
focusing lens such as a Fresnel lens, 4) use multiple flash units set
to discharge simultaneously, 5) increase the flash duration. If
using the latter method, one must be careful not to increase the
duration to the point where blur is seen in the splash.
Information on adjusting flash duration is provided in the links given
at the top of this page.
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