USING CCD CAMERAS
Connections & Interfacing
Video out is generally BNC with cased cameras. Use only 75 ohm cable and
make sure equipment to interface with takes 1V p-p neg sync video. Note
that unless otherwise specified, a camera supplies only baseband video
and audio. You CANNOT connect the camera directly to the cable input or
antenna terminals of a TV set and expect a picture. A VIDEO INPUT jack is
required as well as an AUDIO INPUT jack. Many TV sets have these inputs,
as do VCRs and Camcorders. They are usually standard RCA type jacks. A
shielded cable with RCA male connectors can be used for audio, but the
video will need a BNC male (UG88) at one end and an RCA male at the other
end. For short runs <10 ft. you can use shielded audio cable with two
male RCA plugs and a BNC-RCA adapter but 75 ohm coax is to be preferred for
longer runs. The video cable should be matched to avoid reflections
and ghosting. DC is 12-14 volts CLEAN with little ripple and noise. Case
is generally negative and center pin is positive.
Board cameras usually come with flying color coded leads with connectors
to mate with the PC board. Follow wiring diagrams exactly.
Precautions: Cased cameras and board cameras
If your camera uses it, USE ONLY supplied wall transformer, NO OTHER, or
the camera may be damaged. Many wall transformers are poorly regulated and
produce 50% to 75% more voltage under light load conditions. This may
destroy your camera instantly beyond repair.
A battery pack may be used if an fuse is installed in series with the
hot (generally positive or +) supply lead. Fuse should be rated no more
than twice the camera current drain. A protection diode such as a 1N4007
should be installed in series with the battery supply to guard against
accidental reverse polarity due to incorrect wiring or transients from
other devices sharing the supply.
DO NOT reverse supply leads even momentarily as this will destroy the cir-
cuitry in the camera.
AVOID strong RF fields and static electricity. If used with a transmitter
bypass all leads and keep camera away from antenna. Ferrite beads and a
few 100 pf or 0.001 mfd disc capacitors can be used. Remember that the
video output impedance is 75 ohms and that a 470 pf disc capacitor will
have about this much reactance at 4.5 MHz, so keep video bypasses less
than about 220 pf. Also watch out for ferrite beads causing excessive loss
at higher video frequencies. Cameras can be enclosed in shields made from
cardboard or heavy paper covered with adhesive backed .0015" copper foil
if weight is a problem. This can be found at craft and hobby shops.
DO NOT point camera at very bright lights or the sun. Keep lens covered
when camera is not being used.
NEVER, NEVER attempt to clean CCD device or touch it with finger. It is
static sensitive. Keep body cap on lens opening when no lens is installed.
For cased cameras, DO NOT force lens threads as the aluminum housing has
a fine thread that strips very easily. Check for dirt or burrs before
installing lens. If resistance is encountered find out why. Again the lens
should turn effortlessly, DO NOT FORCE it, or you may jam the lens or strip
the threads. Treat the camera as you would a fine photographic camera and
you should have few if any problems.
Board cameras should be mounted with small hardware and should not have any
strain on the circuit board. Use nylon hardware if possible or use fiber
washers with metal hardware as a strain relief.
CCD camers using fixed lenses may be focused if necessary by using a fine
jewelers screwdriver to loosen the lens mounting screws, then sliding the
lens as needed, while monitoring the video on a monitor or oscilloscope,
adjusting lens for maximum detail(preferred method) or high frequency
content as seen on an oscilloscope. In most cases, CCD board cameras are
focused at the factory and need no adjustment.
Applications and hints for CCD cameras
Standard Wratten photo filters may be used over the lens for effects
B/W cameras have infrared sensitivity and a Wratten #87 filter can be used
to allow only infrared radiation to pass. Sensitivity is near IR region
out to about 1050-1100 nanometers.
A cyan or green filter will correct excessive red sensitivity to yield a
more "natural" tonal scale as the human eye would see. A Wratten #11,
#38, #58, or #61 filter can be obtained from a dealer in photographic
supplies, or a piece of transparent green plastic can be used, if it
is optically suitable. Optical suitability can be determined as follows
If it does not distort your vision in any way, and moving the plastic or
glass filter in front of the eye causes no movement, blurring, or any
distortion of an image to be noticed, it is probably OK for use. A #11
filter is a very common item and is recommended for general use. A coated
filter is best if available as it helps to reduce reflections. Tiffen
or B+W brands are recommended.
Color cameras have built in filtering to correct the high red and IR
sensitivity and therefore will show much less sensitivity to IR. This is
a necessary compromise for correct color rendition. B/W cameras are
therefore best for IR and low light work.
A standard camera tripod may be used as a mount. For cased cameras, thread
1/4-20 screw NO MORE than four threads (0.200 inches) into the camera body.
Light source can be anything handy, or available daylight. Flourescent
tends to be red light deficient and has little IR component, and may not be
as good in low light situations (<1 lux) as tungsten light. A standard 10
to 100 watt clear or frosted bulb is an excellent source for this camera.
For battery powered applications a 12V tungsten or quartz halogen lamp
can be used. Avoid contrasty situations for best results.
Cased cameras many times use C or CS mount lenses much like a 35 mm SLR
camera. This permits use of various lenses for different applications.
To adjust infinity focus for a lens, mount lens to be used. Connect up a
monitor and set up the camera to point at a distant object (> 20 ft).
Set the lens to infinity focus, with iris wide open (if applicable). On
back of camera typically there is a slotted shaft, knob, or other arrange-
ment. Turn with fine tip screwdriver or other suitable tool as needed until
image on monitor is sharpest with lens set at infinity. Check at near
distances to make sure near focus is OK. If needed, you can set this for
close focusing if infinity focus is not necessary. With short focus lenses
(4 or 6 mm) depth of field is tremendous, a few inches to infinity.
A T to C adapter can be used to mount other lenses. Also, a 1.25" adapter
can be used to connect this camera to an astronomical telescope.
Video Astronomy with CCD cameras
A CCD camera can be mounted at the prime focus of a telescope, either a
refractor or a reflector. A C mount to 1.25 inch adapter can be used with
cased cameras. For board cameras, the camera could be mounted in a housing
so that the assembly slips into the focusing tube in place of the eyepiece
and arranged so the CCD sensor is placed at the focal plane. The moon
shows up very well and depending on the telescope aperture, many stars can
be seen. The camera is quite sensitive and is useable for some video observations.
The same setup can be used for terrestrial observation and nature
studies or surveillance applications. A VCR, VTR, or camcorder may be used
to directly record observations if desired. Note that the image of a star
in a good telescope will be a fine point of light, and since a star cannot
be resolved into a disc, the optical quality, seeing conditions, and aperture
of the scope determine the size of the point. Better scopes produce smaller
points of light with little light present in the diffraction rings that
surround the star image. In this case, the amount of light picked up is
proportional to the aperture of the scope. It is possible that this point of
light could fall between pixels on the CCD sensor. This is not a problem
with finite size images as is the usual case, so do not expect the CCD to
perform as well with stars as with planetary or lunar images. Also keep in
mind the inherent red and IR sensitivity of the CCD. Still, excellent
astronomical views may still be had with appropriate optics.
If a TV set with no video input is all that is available, use a video modulator
such as cat # MODU between camera and set. The video and audio are
fed to the modulator and the modulator output connected to the ANTENNA
terminals of the TV set. The video will appear on VHF CH3 or CH4. Note that
the modulator needs DC power, typically 9V at 50 mA.
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