Image Processing Reference
In-Depth Information
This is when you might use your frame grabbing and comparison capability
from the computer. You can shoot a frame with the working light on to see
where the stand and star are in the frame, turn off the working light, perform
and shoot the light painting, turn the working light back on to place the
stand and star in the next position, compare the new placement with the
old working light stand and star placement, turn off the light to perform
and shoot the next light painting, and so forth. The working light has to be
off during the shooting. You need only about eight frames of the rising star
before it bursts, so that is the only period that you may need the working
light setup to measure the placement of the star and stand. If you are using a
program like Dragon to control and shoot your frames, then you can eliminate
the working-light shots from the sequence later in postproduction. This
whole process can be done without the frame comparison capability and no
computer. If you choose to just shoot on a flash card in the camera, then think
about other means of tracking the star guide placement. This could be by eye
or tape on the floor or markings on your stand to guide it as it rises into frame.
The problem with the computer is that it emits light in the dark, which can
reveal more than you want. This can be resolved by putting a cloth over the
screen for each exposure. Programs like Dragon have a “blackout” feature that
darkens the screen during the exposure. I leave this option up to you.
When you place the star on the stand in each position for each frame, you
need to light paint. You must have a light source, and that should be a small
LED flashlight. You can add or tape a colored gel on the front of the flashlight
if you want color. Some small LED lights have color built into them, and that
might be your best choice for colored light. Each time the shutter is open for
the exposure you need to quickly and precisely (as you can) trace the outline
of the star from behind the star allowing for some of the light to spill over and
shine into the camera. It is worth practicing this a few times to see how long it
takes to trace out the star. That time should be your ultimate exposure shutter
speed. You need to take some practice shots to find the proper settings for
your camera and make sure you have the right overall exposure for the light.
I should say that this exercise is best executed by two people, although you
could do it yourself using the self-timer option on your camera or a wireless
remote. Your shutter speed should end up being somewhere between 3 and 5
seconds long with an adjusted aperture to compensate for the long exposure.
Once the star hits its zenith in the frame, you need to remove the stand and
star from the frame for the next shot, which is the beginning of the burst.
You need a memory of where in space the star was in its last position (if you
are not using a frame grabber). When you are ready to shoot the beginning
of the star burst, think about how the light from your LED flashlight should
disperse and work from that central point of the last star's placement. The
first explosion could be a bright powerful beam that you point directly at the
camera, and the sequential frames are the dispersing light trails. You could use
different colored lights for a fireworks effect as the lights get farther out in the
composition for each shot.
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