Baxall OSD Series Manual de usuario

Guide to Cameras and Lenses

PRODUCT SAFETY

WARNIN

• Installation and servicing of cameras is only to be carried out by suitably qualified and experienced

personnel.

• Mains cameras contain hazardous voltages

• Do not remove camera covers as there is a risk of injury or death by electric shock.

• Cameras connected to mains supplies must be earthed.

• Only power low voltage cameras from a class 2 isolated power supply.

Guide to Cameras and Lenses

Contents

Introduction .............................................................................................................................................................. 4

Colour Balance ......................................................................................................................................................... 5

Gamma .................................................................................................................................................................... 6

Automatic Gain Control (AGC) ................................................................................................................................. 6

Electronic Iris (EI) ..................................................................................................................................................... 6

Synchronising Cameras ........................................................................................................................................... 7

Linelock phase adjust (LL-PH) ................................................................................................................................. 8

Backlight Compensation (BLC) ................................................................................................................................ 8

Flickerless ................................................................................................................................................................ 9

Shutter Speeds ......................................................................................................................................................... 9

Sensitivity ............................................................................................................................................................... 10

Resolution ............................................................................................................................................................. 10

Peak White Inversion ............................................................................................................................................. 10

Common Lens terminology ..................................................................................................................................... 11

Choosing a lens ...................................................................................................................................................... 12

Focal Length .......................................................................................................................................................... 12

Fixed Focal Length ........................................................................................................................................... 12

Variable Focal Length ....................................................................................................................................... 13

Lens Formats ......................................................................................................................................................... 13

Lens Mounts ........................................................................................................................................................... 13

Lens Iris .................................................................................................................................................................. 14

Fixed Iris ........................................................................................................................................................... 14

Manual Iris......................................................................................................................................................... 14

Automatic Iris .................................................................................................................................................... 14

Peak / Average Adjustment for Automatic Iris Lenses ................................................................................. 15

Direct Drive DD ................................................................................................................................................. 15

Fitting a Direct Drive Lens Connector .......................................................................................................... 15

DD Lens Level Adjustment for Fixed and Zoom Lenses ..............................................................................16

Depth of Field ......................................................................................................................................................... 16

Adjusting the lens back focus ................................................................................................................................. 17

Camera Mounting ................................................................................................................................................... 18

Cables .................................................................................................................................................................... 18

Guide to Cameras and Lenses

INTRODUCTION

This short guide is aimed at trying to assist installers and engineers to correctly set up and understand the many

advanced features of Baxall cameras.

Almost all of Baxall’s cameras have similar features and functions whether they’re a monochrome or colour version.

Usually, the features are controlled using dip switches that are located under the hinged side door of the camera. A

label on the camera shows the settings for each function.

LL-

230V NOM.

50/60Hz

A.C.

MADE IN EU

POWER

CD9252

LENS

GENLOCK

VIDEO OUT

Function

switches

Genlock

Connector

AI Lens

Connector

Video

Connector

Power LED

Line-Lock

Phase Adjust

DD Lens level

adjustment DD lens

connector

Mounting bush

Back focus

adjustment

Typical Camera Layout

Some cameras in the Baxall range (OSD Series), are set up remotely by means of an on-screen menu system. All the

functions of these cameras can be changed or set via the video coaxial connection.

Guide to Cameras and Lenses

COLOUR BALANCE

As the name implies, this feature is common to colour cameras only. Cameras that have the colour balance feature

generally have four modes of use; Indoor, Outdoor, Fluorescent and Auto.

The white balance feature compensates for the temperature colour ‘casts’ that different light sources can cause.

Colour casts can make white appear with a slight hue under different light sources (e.g. tungsten and fluorescent). To

see the effects caused by different lighting conditions, point a camera set to auto colour mode out of a window. Allow

the camera ten seconds or so to balance to the outside lighting, then point the camera indoors at a room scene lit with

artificial lighting. Any white areas in the scene will show a definite colour tint. After a few seconds you will see the

camera compensate and the white areas will be rendered correctly.

The camera cannot do this unless the colour mode is set to auto colour balance. It will only correctly reproduce white

for the specific lighting type it is set for. Baxall set the three fixed colour modes on their cameras to compensate for

indoor (tungsten), outdoor (daylight) and fluorescent lighting types.

Because no single lighting type has a fixed colour temperature, accurate rendering of white cannot be guaranteed.

Colour compensation should only be used if the scene being viewed contains a number of different lighting types and

this causes the auto white balance circuit to ‘hunt’ as it tries to balance itself. For cameras fitted with this feature,

Baxall recommends that it is always set to Auto. Figure 1 below shows typical colour casts for everyday lighting

Fig. 1. Typical colour casts

Auto White Balance on Outdoor (natural) lighting

Fluorescent lighting Tungsten lighting

Guide to Cameras and Lenses

spectra.

GAMMA

The reproduction characteristics of most cameras and video displays are not linear. For example, imagine a scene lit

with low ambient lighting, a small change in the light level falling on the CCD will produce a given output signal.

However, the same change in light level within a scene lit with strong ambient lighting will not produce the same

magnitude of output signal. This non-linearity is known as gamma and it usually results in poor discrimination of grey

areas in the scene at low light levels.

To compensate for this and improve linearity of the system, Baxall cameras have a built-in gamma correction circuit

which normally has two settings. Usually specified as Normal (0.45) and Linear (1.0) (but sometimes High and Low

respectively), you can choose the optimum setting for the scene being viewed.

The Normal setting has the effect of stretching the camera’s response to the black and mid-grey components of the

scene whilst compressing the white copmonents. This makes it easier to see differences in those shades of grey that

are close to each other and is therefore useful when more visibility is required in darker areas of the scene. However,

the white compression can make it more difficult to differentiate shades of white in lighter areas of the scene. Compare

the grey bars in the two images (figure 2) and notice how the Normal setting seems to ‘reveal’ more of them.

Normal setting Linear setting

AUTOMATIC GAIN CONTROL (AGC)

Baxall cameras contain a video amplifier which applies gain to the video signal as required (up to a maximum of

28dB). The circuit is designed to compensate for fluctuations in scene illumination which would cause the video

output level to be too low. If the video level is adequate, the circuit will not apply any gain to the signal. As the video

level drops (e.g. the scene illumination level falls), more and more gain is applied by the AGC circuit to the video

signal. The camera only applies as much gain as is necessary to bring the video signal up to a reasonable level

(typically 1V peak to peak).

It should be understood that the AGC circuit cannot work miracles and some light must be present within the scene.

Note that as a consequence of amplifying a poor signal, the noise present in the signal is also amplified. Therefore a

poorly lit scene with a lot of gain applied to it will appear noisy or grainy. This is usually accepted in deference to the

alternative of having no picture at all. Obviously, the ideal solution is to provide adequate illumination for the scene

wherever possible.

It is recommended that the AGC feature is left permanently switched on since it will have no effect as long as the

scene illumination is adequate. When setting lens levels, switch the AGC off. This way you can be sure that the

picture you are seeing is not due to the effects of the AGC circuit. After the lens level has been set up, switch the AGC

back on.

ELECTRONIC IRIS (EI)

In contrast to the Automatic Gain Control, the Electronic Iris (EI) feature is used to compensate for increases in the

video level. Consider a camera fitted with a manual iris lens that is being used for low light surveillance. The iris has

to be left fully open so the camera’s performance is not degraded. However, in bright daylight conditions, the video

output level will be excessive and the resulting video display will be overexposed (white-out). The electronic iris can

overcome this problem. The electronic iris feature continuously varies the shutter speed between 1/50s and

Fig. 2

Guide to Cameras and Lenses

1/100,000s (1/60 and 1/100,000s for NTSC cameras) according to the light level. The ‘shutter’ in a CCTV camera

actually regulates the amount of time that light is allowed to fall onto the imaging CCD element. Shorter duration

shutter speeds allow the CCD less time to gather light (or charge) thus preventing overexposure. The EI circuit is

designed to ensure the camera’s video output level is maintained at the optimum value of 1V peak to peak.

Once again, the electronic iris feature has its limits. If too much light falls onto the CCD, it can result in the phenomena

of ‘smearing’. Usually the result of bright point sources of light such as car headlights, smearing appears as a bright

band above and below the highlight. The onset of smearing has reduced as CCD technology has improved, but it can

still occur when the CCD is overexposed.

SYNCHRONISING CAMERAS

There are many surveillance applications where more than one camera is used—to cover a large site for example.

Normally, some means of switching between cameras is employed. If the cameras are not synchronised correctly, the

image on the monitor will roll as the video switcher is used to select different cameras. This is because the video

output from each camera is essentially free running and frames arrive at the video switcher at different times. Baxall

cameras provide several features to ensure synchronisation. The first of these is Line Locking and is selected by a

switch on the side of the camera. When the camera is line-locked, it is synchronised using a fixed point on the A.C.

supply’s cycle—usually the point that the A.C. cycle passes through zero (figure 3). Setting all of the cameras to line

lock mode will ensure that they all output video frames at the same time relative to one another. Obviously, to utilise

this feature, cameras must be operating from an A.C. supply and be on the same mains supply phase.

NOTE: Cameras on different mains phases can still be synchronised (see LL-Phase Adjust below).

A camera set to Line Lock is synchronised

to the negative going zero volt crossing poin

A.C. C

cle

The other way to achieve synchronisation is to use Genlocking. Genlocking requires an externally generated

synchronisation signal which is sent to each camera via a separate coaxial connection. Many Baxall cameras are

fitted with a Genlock BNC to allow the connection of such a device. The generator produces an accurately clocked set

of video timing signals.

Although genlocking is the best way to synchronise cameras, it has obvious disadvantages such as the need for an

extra cable for each camera which can add significantly to the installation costs. In addition, the video generator will

need as many outputs as there are cameras in the system. Figure 4 shows a typical genlock setup.

Video Out

ync In

Sync Out

Sync In

Video Out Synchronising Generator

Video Out

Baxall cameras also have an internal oscillator which is selected using the Internal mode switch. This feature can be

especially useful where the camera is designed to run off a D.C. supply or if a camera designed to operate at 50Hz

(e.g. PAL standard), is installed in a country where the mains supply frequency is at 60Hz. Ordinarily the camera

would not be able to use the Line Lock mode. Setting it to synchronise to its internal oscillator will overcome this

Fig. 3

Fig. 4

Guide to Cameras and Lenses

problem. A side effect of such a setup however may be that the lighting in the scene seems to flicker. This is caused by

the discrepancy in the frequency of the camera (50Hz) and the frequency at which the lights are running (60Hz)

resulting in a mild strobing effect.

LINELOCK PHASE ADJUST (LL-PH)

Cameras can often be supplied from different A.C. phases especially when they are physically remote from one

another or because of the way the site’s A.C. supply is distributed. However, as we have already mentioned, it is still

possible to line-lock these cameras together. A dip switch on the side of the camera allows you to select between

Fixed or Adjustable. Either setting provides line-locking, however the Adjustable setting permits the point of

synchronisation on the A.C. supply cycle to be shifted. A potentiometer, (usually located on the rear panel of the

camera), provides up to 120Oof adjustment either side of the zero volt point. Since supply phases are 120Oout of

phase with one another, this control allows enough adjustment to enable accurate camera synchronisation (figure 5).

Trigger poin

3-phase A.C. C

cles are 120 apart

120

+120

Adjustment range

-120

BACKLIGHT COMPENSATION (BLC)

Backlight compensation is a feature that is often misunderstood or applied incorrectly. Situations frequently arise

where the brightest light in the scene is coming from behind the subject of interest. Imagine a camera monitoring a

doorway. In this example, the light outside the door is much brighter than the ambient light in the room where the

camera is located. The camera’s exposure system sets itself according to the average light level in the scene.

However as someone opens the door the exposure system reacts to the increased light level and as a result, anybody

entering the room is seen in silhouette. The backlight compensation feature can help to overcome this problem and

figures 6 and 7 serve to illustrate BLC control.

Fig. 6 Backlight Compensation off Fig. 7 Backlight Compensation on

Normally, the exposure circuit within the camera takes an average reading from the illumination present in the entire

scene and uses this to adjust the electronic iris (or the lens iris in the case of a motorised lens). Ideally, the camera

would calculate the exposure based on the light level in the part of the scene that is of interest to the viewer. The

backlight compensation feature uses a ‘window’ to set the exposure. Everything outside the window is ignored by the

exposure system.

Fig. 5

Guide to Cameras and Lenses

Indicates area used to calculate the exposure

Fig. 8 Fixed BLC window Fig. 9 User-selectable BLC windows

On most cameras, the exposure window is fixed to the central portion of the scene (figure 8). Some baxall cameras

allow you to choose several different windows (X series cameras); and some cameras allow you to completely control

the size/position of the window and the amount of exposure compensation applied to the selected area (OSD series

cameras). Figure 7 shows the range of selectable BLC windows available on Baxall X series cameras.

The window at the top right in figure 9 would be ideal where the surveillance target is a street scene. The bright sky

area would normally cause the camera to bias the exposure and the street would appear dark in comparison. Setting

a window that forces the camera to ignore the sky will ensure that detail in the street is retained. Note that because the

camera is calculating its exposure based on the lighting in a darker area of the scene, the lighter areas will overexpose

and, in some cases, ‘white out’ completely. This effect can be seen in the background of figure 7.

FLICKERLESS

In some lighting conditions, particularly fluorescent, the image can be seen to flicker. This is usually caused by the

interaction of the shutter with the A.C. frequency of the lighting. The Flickerless setting changes the shutter speed of

the camera to a value that will not cause flicker (1/120s for PAL system cameras; 1/100s for NTSC). The disadvantage

to fixing the shutter speed in this way is that the sensitivity of the camera will be reduced. This is because the

electronic iris feature has effectively been turned off and it will no longer control the optimum exposure setting for the

available light conditions.

SHUTTER SPEEDS

The electronic shutter available on Baxall cameras is analogous to the shutter in a conventional 35 mm camera. The

shutter speed is usually selected using a bank of dip switches located on the side of the camera. A faster (i.e. briefer)

shutter speed can arrest the motion of a fast moving object rendering it sharp. Fast shutter speeds allow less light to

fall on the CCD and can darken the image. If fast shutter speeds are required, ensure that there is adequate lighting.

Selecting a shutter speed manually will override features such as the electronic iris and flickerless settings.

Slow shutter speed Fast shutter speed

Fig. 10

Guide to Cameras and Lenses

SENSITIVITY

The sensitivity of a CCD camera, broadly speaking, is a measure of its performance in low light conditions. Baxall

quote the sensitivity levels of their cameras as the minimum scene illumination required at a given lens aperture to

provide a useable video output. A typical figure may be 0.1 lux @ f1.2. This means that at a lens aperture setting of

f1.2, the minimum scene illumination would need to be 0.1 lux (approximately equivalent to the full moon) in order to

provide a useable video output from the camera. Some manufacturers quote sensitivity figures that require expensive,

‘faster’ lenses (e.g. f1 or better) in order to achieve them. The table below shows some typical lux levels that can be

expected under common lighting conditions.

RESOLUTION

Resolution is the ability of a camera to discriminate fine detail in a scene. The resolution of a camera is usually

expressed in terms of horizontal TV Lines (TVL). Cameras specifications quote resolution based on the number of

horizontal elements that can be captured by the camera and, confusingly, this relates directly to the number of

vertical lines that can be discerned for an equivalent picture height. Typical video display devices have the proportions

of 4:3, therefore equivalent picture height means that only ¾ of the horizontal line is used to quote resolution. This is

done to preserve the natural proportions of the image.

In effect, a camera with a resolution of 570 TVL being is able to display ¾ of a single horizontal line as 570 individual

segments. The higher the number of segments used to display the line, the more fine detail can be resolved in the

image. Obviously the number of horizontal lines displayed vertically (i.e. the vertical resolution) in a given system is

fixed according to the CCTV standard in use (approximately 400 lines for PAL/CCIR; 330 lines for NTSC; etc.).

Cameras are often described as medium and high resolution. This typically equates to medium resolution of 330 TVL

and a high resolution of 480 TVL for colour cameras; and a medium resolution of 380 TVL and a high resolution of 570

TVL for monochrome cameras. If it is important to be able to resolve fine detail in an application, choose a camera

with an appropriate resolution.

PEAK WHITE INVERSION

Some surveillance applications naturally contain many point sources of light — one such being highway monitoring

during night-time where oncoming vehicles have their headlights on. This can cause the camera’s electronic iris, or

the iris of an automatic lens, such as a Direct Drive or Video Drive type, to react and close thereby losing detail in the

darker areas of the scene.

The Peak White Inversion feature found on Baxall OSD and CDX series cameras, can resolve this problem. It allows

the user to render selected areas of the scene above a certain predefined threshold level as black. This stops the

camera or lens reacting to the ‘peak’ white areas which would normally cause it to incorrectly control the iris mechanism

thus preventing underexposure of the scene. Figure 11 shows a typical application of the Peak White Inversion feature.

LIGHTING LUX LEVEL

Unobstructed sun 100,000

Sun with light cloud 70,000

Sun with heavy cloud 20,000

Home/office lighting 100 - 1000

Sunrise/sunset 500

Street lighting 1 - 10

Twilight 4

Full moon 0.2

Quarter moon 0.02

Overcast moon 0.007

Clear night sky 0.001

Average starlight 0.0007

Overcast night sky 0.00005

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