USING CCD CAMERAS
 
Interfacing CCD Cameras is fairly straightforward,connections are usually flying leads or manufacturer supplied inline connectors with PC board cameras. 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 and when hand wiring these units make sure to 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.
 
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. Low light focusing can be checked in sunlight by using a #10 welding filter over the lensIn 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 usually best for IR and very 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. With very sharp lenses, 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.

 

TECHNICAL INDEX

 

NORTH COUNTRY RADIO
PO Box 200, Hartford NY 12838-0200
EMAIL: support@northcountryradio.com            Tel 518-854-9280           Internet http://www.northcountryradio.com