Axis 2400+ Manuale Utente Scaricare il pdf (Pagina 26)

• CS-mount. The distance between the sensor and the

lens should be 12.5 mm

• C-mount. The distance between the sensor and the

lens should be 17.5 mm. A 5 mm spacer (C/CS adapter

ring) can be used to convert a C-mount lens to a CS-

mount lens

Sensor size

The lens must make an image large enough for the

sensor. The larger the sensor, the more expensive the

lens will be. A lens made for 1/2” will work for 1/2”,

1/3” and 1/4” sensors, but not for a 2/3” sensor. If you

use a lens made for a smaller sensor on a bigger sensor,

the image will get black corners.

Focal length

The focal length combined with the sensor size gives the

viewing angle. A small focal length gives a wide-angle

view. A large focal length gives a narrow telephoto view.

Wide-angle lenses have a better depth of ﬁ eld than

telephoto lenses. This means you can focus close up to

the camera as well as at a distance. Telephoto lenses

require a more precise focus adjustment.

Three main types of lenses

• Mono-focal. The focal length is ﬁ xed, e.g. 4 mm

• Zoom. The focal length can be adjusted within a

range, e.g. 4 to 10 mm. Focus stays when the focal

length is changed

• Varifocal zoom. This is a lower cost zoom lens.

When the focal length is changed, the lens has to be

refocused. The most common type is 3.5-8 mm

Example

What width of objects will you be able to see at 10 ft if you

have a camera with a 1/4” CCD sensor and a 4 mm lens?

H = D x h / f = 10 x 3.6 /4 = 9 ft

Choosing the right lens

There are two main mounting standards. They both have a 1” thread and

they look the same. If you ﬁ nd it impossible to focus your camera, then you

probably have the wrong type of lens.

The ﬁ gure shows a schematic drawing of a lens. A lens usually has 4-10 lens

elements.

f =h D

1/4" Sensor: h=3.6 mm

1/3" Sensor: h=4.8 mm

1/2"Sensor: h=6.4 mm

f =Focal length

Here you see the formula for calculating focal length.

C AMERA BASICS

FOCAL LENGTH

MOUNT IRIS

SENSOR SIZE

1/4", 1/3", 1/2", 2/3"

WIDE ANGLE

TELE

f = h

1/4" Sensor: h=3.6 mm

1/3" Sensor: h=4.8 mm

1/2" Sensor: h=6.4 mm

f = Focal length

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Axis 2400+ Manuale Utente Pagina 26

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