By adding a night
vision module to a digital SLR camera, night
turns into day. Follow these guidelines to
assure the best possible image quality.
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Today's digital
SLR cameras offer the photographer full control
of aperture, shutter speed and ISO settings enabling
the capture of excellent usable images in low light
that were not otherwise possible. However, in many
situations such as photographing scenes at night
with very little ambient light, or telephoto photography
at night at a distance, even the best digital SLR
cameras simply do not have sufficient sensitivity
to capture adequate images. In these situations,
night vision modules such as those described here
are the ideal accessory. This article provides
important guidelines for producing awesome night-time
photos when using a night vision module-enabled digital
SLR camera.
Because of the increased availability
of high performance digital SLR cameras, capturing
excellent photographs at night is now easier than
ever. With full control of aperture and shutter speed
settings as well as electronic gain (ISO), the photographer
has the opportunity to capture images in low light
that were not otherwise possible.
However, in
many low-light and night-time situations, digital
SLR cameras simply do not have sufficient sensitivity
to capture adequate images. For one thing, with
the ever-decreasing size of pixels, it’s
remarkable that light sensitivity has not substantially worsened with
each new generation of camera (since light sensitivity
is directly proportional to detector pixel area).
But, fortunately, there’s been a lot of camera
development on noise reduction so sensitivity has
kept pace if not improved slightly with the decreasing
pixel area. Regardless of these changes, it remains
that a sufficiently long exposure time cannot be
used because either there is movement in the scene
or the camera is moving (by being handheld or on
a vehicle in motion) so long exposure times would
result in blurring. For situations such as photographing
scenes at night with very little ambient light,
or telephoto photography at night at a distance,
even the best digital SLR camera will be unable
to produce adequate photographs without blur.
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In
these situations, a night vision module such as
those described here are the ideal accessory (www.nightvisioncameras.com). Such
a device fits between the SLR objective lens and
the camera body and amplifies the light that is
captured by the objective lens, projecting an amplified
(but entirely green) image onto the digital camera’s
image sensor. The result is up to 10 F-stops of
improvement, a dramatic change enabling many applications
that are otherwise impossible to photograph. The
module transforms moonlit or starlit scenes into
bright, high resolution images that are easily
photographed. (See box below on
How Night Vision Works).
Below are some guidelines to help
assure that the Night Vision digital photos are
the best possible.
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Exposure Mode
 Select
Manual exposure mode (“M”). Not “Automatic”, “Aperture
Priority”, “Shutter Priority”, “Program” or
any of the other special modes. In low light,
you'll want to manually open the lens
iris to permit the most light to fall on the
night vision module's sensitive photo
cathode.
Shutter Speed Setting
You'll want to set the
camera's shutter speed so that it is
just long enough that there will be no blur
due to motion, usually about 1/30th second.
Longer exposure times will usually result in
blur (for handheld applications). Shorter exposure
times may provide some improvement if excessive
motion is a concern but could unnecessarily
darken the image due to the reduction of light
being acquired from the night vision module's
image intensifier. While the output brightness
from an image intensifier increases with increasing
scene illumination, at higher scene illuminations,
the image intensifier's output brightness
reaches a maximum value and remains constant
as shown in the accompanying chart. (The limitation
on the output brightness protects troops wearing
night vision goggles from being blinded when
viewing a bright light). Since this maximum
brightness is not very bright (about 2 foot
lumens), it is unlikely that the digital camera's
sensor will be saturated as a result. So, faster
shutter speeds are not necessary as a method
to limit the light accumulation.
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ISO Setting
 While
back in the days of photographic film, ISO was a characteristic that described film sensitivity to light, today, ISO is related to electronic gain of the digital camera's sensor. Since increasing the gain will amplify the low light level images, even with a night vision module, lower light scenes will become visible. However, there are disadvantages to setting the ISO too high. As with all electronic circuits at high gain, image noise can degrade image quality. As such, set the camera's ISO to a value as high as you can while still acceptable image noise levels. Usually, the minimum value would be 800, but some cameras deliver perfectly usable images at ISO 1600, 3200 or even 6400 (on some recent Nikons).
Manual Focus
 When using a night vision module, select Manual Focus mode (usually a small lever switch on or near the objective lens mount). Manual focus gives you greater control over how the focus appears. Since night vision modules are generally grainy, the image grain can confuse the SLR camera's focus sensors. Also, realize that these focus sensors will be staring at the output of the night vision module so the grainy artifacts will not be affected by the focus position of the objective lens (which is located on the front of the night vision module).
Use Stabilized Lenses
 A camera's image stabilization feature permits the photographer to use slower shutter
speeds without resulting in blur due to camera
shake. Note that there are two primary techniques
for image stabilization: optical stabilization
(where a small element inside the lens moves
in order to stabilize the image projected on
the camera's detector) and digital stabilization
(which take advantage of extra rows and columns
on the perimeter of the detector, shift the
image an appropriate amount to stabilize certain
types of motion). Normally, the optical image
stabilizers, though more expensive, are preferable
since they better remove the blur component
of the motion. When using a night vision module,
the main disadvantage of the digital stabilization
is that the image is blurred on the input of
the night vision module resulting in some blur
on the intensified output image. So, optical
stabilization is preferred.
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Lens Aperture
The basics still apply for night
vision intensified low-light photography. In
low-light situations, you’ll want to
select the fastest objective lens set to the
lowest F-stop setting. (The lowest F-stop value
indicates that the iris is opened up fully
and will gather the most ambient light possible
for that lens).
| Nikon and Canon offer
fast stabilized telephoto objective lenses
that are ideal for night vision applications. |
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Infrared Illuminator
Sometimes, even with a night
vision module, it’s simply too dark to
obtain a good quality photograph at night.
A dark and cloudy night with no ambient light
is one example. Since the night vision module
is merely a light amplifier, if there is no
light from the stars and sky or from city lights
reflecting from clouds, the night vision module
will not be effective. In order to photograph
without the use of a flash or visible light
source, a near-infrared light source can be
used that emits light that can be seen by the
night vision module but is invisible to the
naked eye. Unlike some digital camera sensors
which have some near-infrared response, night
vision modules are most sensitive to the near
infrared wavelength range and consequently
these light sources can significantly enhance
the night-time image and render night photography
possible despite the lack of sufficient visible
illumination.
Invisible near infrared
illumination can be used to brighten scenes
that are otherwise too dark.
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Image Cropping
 Because
image intensifiers have automatic electronic
gain features to maintain a constant light
output, the presence of bright lights in the
field-of-view (such as headlights or street
lamps) may have the affect of decreasing the
unit’s overall light gain. This is similar
to back-illuminated scenes for un-intensified
photography, but even more important because
of the significant impact on light gain that
could result. This affect may cause the other
regions in the image to darken to an unacceptable
level. If possible, do your best to exclude
non-important bright lights from the field
of view.
Turn-off All Camera Visible/Audible
Functions
For covert night vision photography,
don’t forget to disable all camera lighting
and sound functions. (For example: disable
flash, any red eye reduction mechanisms, auto
focus assist, LCD preview, and all audible
signals).
Use a Tripod
When handheld use is not required,
select an exposure time long enough that the
movement of objects under observation does
not result in image blur. As with un-intensified
photography, long exposures require that you
hold your camera perfectly still to avoid blurring.
A tripod is a perfect accessory. If one is
not available, try bracing your camera against
a stationary object like a tree or wall. In
order to avoid the blur that results from finger
pressing the camera shutter release (which
can cause enough movement to blur a photo),
use the camera’s timer.
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AstroScope
transforms dark scenes into bright, high
resolution images that can be easily photographed
without the need for additional lighting
or longer exposure times. The objective
lens focuses the minute amounts of available
light onto the faceplate of its internal
central intensification unit that converts
the photons to electrons. The internal
electron flux is then amplified and the
electrons are accelerated so that when
they impinge on the output phosphor, a
bright green image is created. The image
is then focused onto the internal detector
of the digital SLR camera. 
