In this image, the photographer attempted to reveal the movement of the helicopter’s rotor blades by
leaving the shutter open long enough to create a motion blur. However, it also allowed more light to
fall on the image sensor, resulting in an overexposed picture. This photo was taken from the ground.
and your image is still coming out
underexposed, your only option is to
add more light by waiting for a sunny
day, changing the position of your
subject relative to the sun, or using
Most larger, purpose-built cameras—
unlike those you find on cellphones
and prosumer-level drones—give you
another option of opening up the
aperture. Aperture is a fancy word for
the opening in the lens where light
comes through. Make it bigger and you
let more light fall onto the sensor.
The size of the hole is reflected by
the f-stop of the lens, with f/2 being
a big hole, and f/22 being a tiny hole.
However, adjusting the f-stop of the lens
involves another set of tradeoffs and isn’t
an option on most drone cameras, unless
you’re flying a professional-grade aerial
cinema rig. In that case, you became
bored and stopped reading a few
Take My Temperature
Another concept to be aware of is
color temperature, which is closely
related to white balance. It will not
surprise anyone who has ever hung a
string of holiday lights to learn that
light comes in different colors such
as red, blue, green, yellow, and so on.
However, what is considerably less
obvious to the casual observer is that
you encounter different colors of light
every day as you go about your life.
For example, the light shining
down from the sun on a clear day
is a different color than on a cloudy
day, and incandescent bulbs are
different from fluorescent tubes. These
differences are categorized by color
temperature and are measured in
degrees Kelvin (K). This has nothing to
do with the actual temperature you feel
on your skin—only the hue of the light
falling onto it.
As an example, a candle flame falls
at approximately 1,850 K, which is the
same as a sunset or sunrise. A standard
incandescent bulb is approximately
2,400 K, and a typical fluorescent tube
gives off light at approximately 5,000 K.
The light coming down from an overcast
sky is close to 6,500 K.
Of course, the color of the light falling
on an object affects how that object
appears, which is how we arrive at the
concept of white balance. A sheet of
white paper will appear to be green if
it’s lit by a green light; therefore, if you
want it to appear white, you need to
recalibrate the camera to take that
102 Model Aviation JULY 2017 www.ModelAviation.com
ADVANCED FLIGHT TECHNOLOGIES