Choosing Cameras for the PX101/PX201 series
? J. Kovacs, Nov 07, 2001
Note: With the introduction of our PXD series of advanced DSP based split screen controllers, genlock cameras are no longer required. The PXD series will work with most analog NTSC, PAL, EIA or CCIR video cameras.
The MicroImage PX101/PX201 video split screen/fader series is designed to accept two NTSC RS-170 composite video (PX101EX), S-video (PX201EX), or PAL-compatible composite (PX101EXP) inputs or S-Video (PX201EXP), either B&W or color. If using one of the NTSC models, both incoming signals need to be NTSC compatible. For the PAL models, all signals must likewise conform to PAL standards. In either case, ONE of the cameras must have full genlock capability.
The first camera or other RS-170 compatible video source connects to the CAMERA A input of the video fader. From this input it generates a composite genlock signal, which appears on the GENLOCK B output BNC connector, and separate horizontal drive (HD) and vertical drive (VD) pulses, which are available from the H/V DRIVE mini-DIN connector. The composite genlock signal is also routed to one of the pins of the mini-DIN.
The video source selected for the CAMERA A input does not need to be genlockable, but must conform to strict RS170 (for PAL, CCIR) specifications. This allows for the use of a wide variety of equipment, including older or less expensive cameras and other video signal sources. Since camera B derives its timing from the A source, its image stability is dependent on that of camera A.
Camera B MUST have genlock capability. One video cable must be connected from the B camera’s output to the CAMERA B input on the PX101/PX201. A second cable goes from the GENLOCK B output BNC connector on the PX101/201 to the genlock input of the B camera. In some cases, as when long cable runs are required between the PX and the cameras, better results may be obtained by running the genlock cable from a video output on camera A directly to the genlock input on camera B. As an alternative, if synchronization with other equipment is required, the genlock inputs of both video sources may be connected to an external sync generator. The PX will then derive its own synchronization from the A camera video signal.
For color applications, the B camera MUST also have a subcarrier (SC) phase control to match the colors between sources A and B. Since even a few feet of standard video cable produces enough phase shift to cause a noticeable color variation between cameras, this adjustment is essential. Many of the cameras which lack an SC phase control randomly lock to one of four phases on power-up, which makes color correction difficult or impossible. Typically, phase controls can shift the colors through a full 360 degrees. If the control does not have sufficient range in one direction, try rotating it in the opposite direction. A smaller number of cameras use switches for an SC phase coarse adjustment, or a combination of coarse and fine controls. Several of the newer cameras set phase adjustment through an on-screen menu. <SEE GENLOCK AP. NOTE>
In situations where there is no alternative other than to use a non-genlockable camera, a frame synchronizer or time base corrector may be able to break the video signal down into its constituent parts and reconstitute it in a usable, genlocked form.
Also see? AN005: An Overview of Genlock