Specifications

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HD-CCTV SYSTEM
Zoom performance comparison using actual cameras
If we compare the legibility among cameras through the formula of “Focal-length at Tele-end x Resolution Factor = Virtual
focal-length at tele-end”
From the above results, camera 2 shows similar legibility to 29x (137.9mm/4.7mm), analog zoom camera, and camera 3 shows similar legibility
to 49x (230.3mm/4.7mm) analog zoom camera. In other words, judging the zoom performance of HD-SDI and analog camera by simply their
zoom magnication may bring wrong result.
That is, even through camera’s “Focal length at Tele-End” is same, the actual legibility shows dierence according to camera’s resolution.
Camera1
Analog 35x zoom camera (410K pixels, 720 x 480)
Focal length : 3.4mm ~ 119mm
119mm x 1 = 119mm
Camera2
HD-CCTV 18x zoom camera (720p, 1,280 x 720)
Focal length : 4.7mm ~ 84.6mm
84.6mm x 1.63 = 137.9mm
Camera3
HD-CCTV 20x zoom camera (1080p, 1920 x 1080)
Focal length : 4.7mm ~ 94mm
94mm x 2.45 = 230.3mm
Legibility of HD-SDI zoom camera (vs. analog camera)
To get the optical performance of lens, we may simply compare the focal-length of lenses. But, it is somewhat risky to judge
the zoom performance only based on the zoom magnication which is calculated by the focal-length ratio of Tele-end and
Wide-end. Several factors like resolution of lens itself and light transmittance aect the actual legibility of zoom camera.
In the following case, zoom performance of two 35x and 37x camera is almost same, but actually 35x zoom camera will show
better zoom performance. In other words, the higher zoom magnication does not mean the better legibility.
Legibility comparison between analog and HD-CCTV camera based on resolution
You may consider 20x HD-CCTV camera may have lower legibility if it compared with 35x analog camera because it has lower
zoom magnication, but it it not true. Because HD-CCTV camera is using 2 megapixel image sensor, it provides much greater
information than analog camera which uses 410Kpixel image sensor. Moreover, HD-CCTV is using digital video transmission
method so, it prevents the drop of video quality during transmission, and it keeps relatively higher legibility.
More technically, let’s compare the pixel quantity between HD-CCTV camera and analog camera. NTSC video can be convert-
ed to digital video, and its maximum size is as follows.
Many conventional zoom camera and speed dome customers had been judged zoom performance based on focal-length
at Tele-End, and zoom magnication. But, if we compare the HD-CCTV camera with conventional analog camera, we need
more deep study. Because HD-CCTV camera has much higher resolution than analog camera, it is not suitable only to use lens
magnication to compare the legibility between the videos.
Therefore, HD-CCTV’s total pixel is exactly 6 times bigger than analog’s one. Because √6=2.45, it means HD-CCTV camera has
same eect as using a zoom lens which has 2.45 times better performance compared to an analog camera.
· Camera A : 35x optical zoom (f=3.4 ~ 119mm)
· Camera B : 37x optical zoom (f=3.2 ~ 118.4mm)
· Resolution of HD-CCTV camera : 1920 x 1080 = 2,073,600 pixels (HD1080p)
· Resolution of Analog camera : 720 x 480 = 345,600 pixels (NTSC)
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