FREQUENTLY ASKED QUESTIONS - F
Focal Length - the distance from the surface of the lens and its focal point.
A full frame of video is the combination of two image fields interlaced together. A frame is one basic screen capture taken by a camera. 30 frames are displayed in one second of real time video for NTSC format. PAL format is phased at a rate of 25 frames per second for real time.
Frames per Second (FPS)
Frames per Second (FPS) describes the number of full video frames displayed or recorded within one second. True real time video consists of 30 frames/sec. for NTSC format and 25 frames / sec. for PAL format. Be sure not to confuse frames per second with "fields per second" or "images per second". A complete frame of video is compiled of two separate images (or fields), so the number of fields in one second is always twice the number of frames per second.
FPS Display Rate (a.k.a. screen refresh rate)
FPS Display Rate (a.k.a. screen refresh rate) indicates the number of frames per second a VCR or DVR recorder will display on a monitor for simultaneous viewing. This shouldn’t be confused with FPS Record / Playback Rate. The rate at which each camera is displayed is often NOT the same as the number of frames per second the recorder captures for playback. Many DVR sellers flash "real time display rate" or "30 frames/sec. display rate" but do not in fact offer real time playback of recorded video.
FPS Record Rate
FPS Record Rate describes exactly how many frames per second a video recorder can actually capture. Analog recorders like VCRs can easily record in real time (30 frames / sec. for standard NTSC) or time lapse (fewer than 30 frames/sec. for NTSC). Many digital DVR recorders, can record actual real time video. For most situations, recording rate is the spec to pay attention to. (Specifications for digital video equipment are not the only numbers to rely on. In fact, many DVR recorders outperform their specifications upon real world testing while other low quality units often record at a much slower rate than their specs claim).
Frequency is the number of competed cycles of an electronic signal that occur in a given length of time. Frequency is usually measured in cycles per second (Hertz, Hz). For most CCTV industry equipment, frequency is used to describe the RF radio frequency at which wireless equipment operates. Frequency can also be used to describe the cycles of electrical current for the signal system.