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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