D-Link DCS-1100 - mydlink-enabled Wired Network Camera Uživatelský manuál stáhnout pdf (Strana 27)

105

F-Number & Exposure

 F-Number, also known as focal ratio, define light-gathering ability of a lens –

the amount of light allowed to pass through the lens.

 F-Number, f/#, is the ratio of lens’ focus length to diameter of the lens

aperture.

f/# = N = f/D

f is focal length, and D is diameter of lens’ aperture. Common F-number on

a lens are f/1, f/2, f/4, f/8, etc.

 The lower the f-number, the more light can pass through the lens. This kind

of lens perform better and produce higher quality image in low-light situation

compared to lens with higher f-number.

IP Surveillance Essential

• Lens Elements

F-number f1.0 f1.2 f1.4 f1.7 f2.8 f4.0 f5.6

% of light passed 20% 14.14% 10% 7.07% 2.5% 1.25% 0.625%

106

Manual or Automatic Iris

 In camera, a diaphragm is an opaque structure with an aperture in its center

to limit the amount of light that passes through the lens. Most of modern

cameras use adjustable diaphragm called an iris diaphragm or often

referred as an iris.

 Manual Iris

• Lens with manual iris usually provides either a ring for users to manually adjust

the iris, or the iris is fixed at a specific f-number.

• Manual iris lens is most suitable for environments with constant light level such

as indoor environments.

 Automatic Iris

• Lens with automatic iris, the aperture of the iris is automatically adjusted and

controlled by the camera processor to maintain optimum light level to the image

sensor. Generally, camera processor controls the automatic iris via direct current

(DC) thus automatic iris is also known as DC-iris.

• Automatic iris lens is most suitable for outdoor environment where the light level

is constantly changing.

IP Surveillance Essential

• Lens Elements

107

CCD Technology

 CCD (Charge-Coupled Device) sensor is a mature sensor technology that

has been used in cameras.

 Special process is used in CCDs manufacturing to create the ability of CCD

to transmit charge across the chip without distortion thus CCD has better

light sensitivity and produces less noise image than CMOS sensors.

 CCD complex process consumes a lot more power, as much as 100 times

more power than CMOS sensor.

IP Surveillance Essential

• Image Sensors

108

CMOS Technology

 Compared to CCD sensors, CMOS (Complementary Metal Oxide Semiconductor)

sensors offers more integration and functionality on the chip, with lower power

dissipation at chip level, and faster readout, which are important advantages for

producing high quality image.

 CMOS is cheaper as compared to CCD sensor because the chip can be fabricated

on almost any standard silicon production line.

 Light sensitivity of CMOS sensors is lower than CCD sensors because each pixel on

a CMOS sensor has several transistors located next to it, thus many of the photos hit

the transistors instead of the photodiode.

IP Surveillance Essential

• Image Sensors

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