Lens Focal Length may be calculated after determining DISTANCE to SCENE (DS) from CCTV Camera and the WIDTH of SCENE (WS) required at that distance.

Focal Length of Lens = (DISTANCE to SCENE × 4.8) ÷ (WIDTH of SCENE).
All measurements in mm [equation for 1/3" Sensor, 4.8 mm wide × 3.6 mm high]

Focal Length of Lens = (DISTANCE to SCENE × 3.6) ÷ (WIDTH of SCENE).
All measurements in mm [equation for 1/4" Sensor, 3.6 mm wide × 2.7 mm high]

Focal Length of Lens = (DISTANCE to SCENE × 6.4) ÷ (WIDTH of SCENE).
All measurements in mm [equation for 1/2" Sensor, 6.4 mm wide × 4.8 mm high]

For example if DS = 1500mm, WS = 2000mm, Sensor = 1/3" equation is:
(1500 × 4.8) ÷ 2000 = 3.6.

A 3.6 mm focal length lens will provide an on-screen image of a scene 2000 mm wide at a camera distance of 1500 mm. In practice results may vary ± ~15% due to component tolerances, variations in image sensor dimensions and monitor over-scan.

Other transpositions of equation:

To Find:

Width of Scene = (DISTANCE to SCENE × 4.8) ÷ (Focal Length of Lens).
All measurements in mm [equation for 1/3" Sensor, 4.8 mm wide × 3.6 mm high]

Width of Scene = (DISTANCE to SCENE × 3.6) ÷ (Focal Length of Lens).
All measurements in mm [equation for 1/4" Sensor, 3.6 mm wide × 2.7 mm high]

Width of Scene = (DISTANCE to SCENE × 6.4) ÷ (Focal Length of Lens).
All measurements in mm [equation for 1/2" Sensor, 6.4 mm wide × 4.8 mm high]

To Find:

Distance to Scene = (Width of Scene × Focal Length of Lens) ÷ (4.8).
All measurements in mm [equation for 1/3" Sensor, 4.8 mm wide × 3.6 mm high]

Distance to Scene = (Width of Scene × Focal Length of Lens) ÷ (3.6).
All measurements in mm [equation for 1/4" Sensor, 3.6 mm wide × 2.7 mm high]

Distance to Scene = (Width of Scene × Focal Length of Lens) ÷ (6.4).
All measurements in mm [equation for 1/2" Sensor, 6.4 mm wide × 4.8 mm high]

Lens Selection Guide for CCTV Cameras with 1/3 Inch Image Sensor

Scene width is directly proportional to Lens - Object distance, for example a 3.6 mm lens (1/3" Sensor) at 1.5 metres captures a scene width of 2 metres, at 3 metres width is 4 metres, at 6 metres width is 8 metres, etc. etc.

Image height is 75% of width.

Figures in tables are calculated values, no allowance has been made for manufacturing tolerances, variations in image sensor dimensions or Monitor 'Over-Scan'.

If a common Video Monitor or TV is used to display images, up to ~ 15% of the image may be lost in 'Over-Scan' and be unseen.

If images are displayed on a PC Monitor using either our VIDEO-VGA converter or a PC Digital Capture Card & Computer 100% of the image will be displayed.

Lens Selection Guide for CCTV Camera with 1/4 Inch Image Sensor

Lens Selection Guide for Camera with 1/2 Inch Image Sensor

Calculate: 2/3", 1/2", 1/3", 1/4" CCD Horizontal and Vertical angles for 2 mm ~ 400 mm focal length lenses.
Calculate: Width and Height at 60 mm to 500 metres for 2 mm ~ 400 mm focal length lenses on 2/3", 1/2", 1/3" or 1/4" CCD CCTV Cameras.

Zero Backlash Focussing System for CCTV Board Lenses. Eliminates "Float" between thread of Lens and Lens Holder, holds lens more perpendicular to CCD (no skew due to lens lock screw) very fine precise focussing is possible and a lens locking screw is unnecessary.

CCTV BOARD LENSES Consist of 3 to 6 Elements, they produce images with good overall focus. These are manufactured in a variety of  thread sizes, our cameras and lenses have a 12 mm x 0.5 mm pitch.

FOCAL LENGTH: We stock 2.1 mm to 25 mm. SPEED: F1.8 to F2.5. The sizes that are suitable for a particular camera are listed on Camera product Web Page.

CCTV PINHOLE LENSES Used on tiny video camera modules for covert and discreet monitoring consist of a simple single Element, focus and transmittance is compromised for small size, diameter of Lens "Hole" is ~ 2 to 3 mm.

C & CS MOUNT CCTV CAMERA LENSES The C Mount is widely used in CCTV (also used on some 16 mm Film cameras), it is a 1 inch diameter 32 TPI (Threads Per Inch) mount. The Flange-Focal-Distance to the image plane of a CS Mount is ~ 12.5 mm and C Mount ~ 17.5 mm. C Mount lenses may be used on CS Mount CCTV Cameras by fitting a 5 mm 'spacer ring'.

IRIS TYPES: Our Board, Pinhole and C Mount lenses are Fixed Iris, the light transmittance can only be reduced by fitting a filter in front of or behind the lens. A Manual Iris lens has an adjustable Iris to control light transmittance, an additional benefit of this is an increasing depth-of-field as the iris is closed. While transmittance can be varied with filters or by varying iris size, the low light sensitivity of the system will be reduced unless the filter is removed or iris opened. An Automatic Iris lens varies iris size based on the level of illumination and may be fully open in low light, user adjustable Level and Metering controls allow tailoring of characteristics to cope with most back-lit and other problem situations.

The composite video output from CCTV Cameras, Modules, Switchers, Quad Processors etc., may be connected to the "Composite Video" or "Audio Visual" (AV) input socket commonly fitted to Monitors, Television Sets, Video Recorders, Computer Video Capture Cards, Transmitters, TV RF Modulator (ie UHF-MOD) etc.

By fitting a UHF-MOD (CCTV-TV/VCR Interface Module) in coax cable between the TV Antenna and Splitter, TVs and VCRs connected to the antenna system may be tuned to receive Video and/or Audio, several UHF-MODs may be used on different channels with multiple cameras.

Our CCD CCTV Video Cameras utilise an Automatic Electronic Shutter (AES) system, this varies the period (shutter speed) during which an electrical charge is accumulated by the CCD Detector Elements, period varies (depending on type) from a maximum of 20 milliseconds to a minimum of 10 microseconds 2000 Times.

The AES will cope with most normal interior lighting conditions, over exposure is likely in brightly lit areas with our Hi-Sensitivity cameras and with OUTDOOR DAYLIGHT scenes. Over Exposure may be reduced with a Manual Iris Lens, Automatic Iris Lens, Neutral Density, Polarising and some other Filters.

THE IDEAL Over-Exposure SOLUTION:
For daylight or high levels of illumination if  'Low Light' sensitivity is to be retained, an 'Automatic Iris' Lens and C/CS Mount CCTV Camera will produce the best result.

An automatic Iris Lens controls exposure by mechanically varying it's 'Iris' size in response to the light intensity at CCD sensor. Other benefits from using an Auto Iris lens are reduced vertical smear (vertical streaks from bright areas in the image) this CCD characteristic becomes more noticeable at higher shutter speeds, the 'Depth-of-Field' is also increased when the Iris closes.

Our CS Mount Japanese Lenses produce Sharper Images and pass more than 2 X more light than most common C Mount Fixed Iris Lenses, use a CS Mount Japanese Lens for 'Crisper' images, to improve Low-Light performance of Video Camera / Lens combination and for Lower-Noise images.

COMPROMISE Low-Cost Partial Over-Exposure SOLUTIONS:

Variable Density or Polarising Filter: A variable density filter can be constructed with two Polarised Filters (FIL-Polxxx), rotating the filters with respect to each other will vary light transmission.

In some situations (low sensitivity Colour CCTV Cameras) a single Polarised Filter may be adequate.

Manual Iris Lens: The Iris can be manually opened and closed to control exposure.

The solutions above will resolve problems due to high levels of illumination, however the combined Camera / Lens sensitivity is reduced considerably, results at night or in low light will be quite poor unless the Filter is removed or Iris is fully opened, the Infrared filter solutions below partially address this problem when using a monochrome camera.

InfraRed Pass CCTV Filter: The camera (Monochrome) may be operated in the Infrared Spectrum only, this can be achieved by fitting a Visually Opaque 670 nm or 730 nm Infrared Pass Filter (FIL-IR670) or (FIL-IR730) over the front or rear of the lens, or the Image Sensor.

InfraRed Cut Filter: The camera (Monochrome) may be operated in the Visible Spectrum only, this can be achieved by fitting an Infrared Cut Filter (FIL-IRCUT) over front or rear of lens, or the Image Sensor.

The Infrared solutions above allow the characteristics of different Lamp types to be used to advantage:

The majority of the radiation from Filament type lamps (Common Spot Lamps, Tungsten, Halogen, etc) is Infrared, therefore little of this energy will be attenuated by an IRP filter.

The majority of the radiation from Cold type light sources (Fluorescent, Mercury/Sodium Vapour, etc) is Visible, therefore little of this energy will be attenuated by an IRC filter.

Infra-Red 'Pass' and 'Cut' Filters will also attenuate transmission of the 'desired' spectrum, reducing the overall 'sensitivity' of camera.

Long term over exposure (Daylight and Artificial) will cause deterioration of CCD Image Sensor, this occurs regardless of whether the camera is powered on or off.

A combination of Infra-Red and Visible illumination degrades overall focus and image quality, Resolution, Sharpness, Contrast and Colour-to-Grey Conversion will be improved, with an Infra-Red 'Cut' (FIL-IRCUT) filter or Lens with an Integral IR-CUT Filter.

When using Infra-Red Illumination only, lens setting for sharpest focus will differ from best setting for Visible or mixture of Visible and Infra-Red illumination.

An Infra-Red 'Pass' filter (FIL-IR670) or (FIL-IR730) will allow adjustment of focus in Day or Artificial Light, readjustment is then unnecessary with Infra-Red Illumination only.

Infra-Red 'Pass' and 'Cut' Filters will also attenuate transmission of the 'desired' spectrum, reducing the overall 'sensitivity' of camera.

The Relative Response (Spectral Sensitivity Characteristic) of a typical Silicon CCD Image Sensor (SONY) is approximately:

0.5 @ 400 nm
1.0 @ 530 nm
0.35 @ 730 nm
0.025 @ 950 nm

This needs to be taken into consideration when choosing an Infra-Red Illuminator, shorter wavelengths are 'seen' by the CCD as brighter.

Relative response of a typical CCD sensor to 830 nm wavelength is ~ 14%, response to 940 nm wavelength is ~ 4%.

Angle of view or width of a scene at a given distance depends upon the focal-length of the lens and CCD Sensor size (1/4", 1/3" or 1/2"). When choosing the focal length of the lens, consideration needs to be given to the purpose of the system, general observation to detect activity/movement, or the ability to identify a person. Also dependent on the purpose is the resolution of any recording and/or display device(s).

For example:
A wide-angle CCTV lens may allow observation and detection of activity in a large area, however detail will be limited.

If the lens is chosen to give a scene width of 5 metres at a particular distance, it will be difficult or impossible to identify a person at that distance. A human head is ~ 20 cm wide, with a scene width of 5 metres it will be ~ 1/25 th of the image width. If the camera has a horizontal resolution of ~ 480 lines horizontally there will be ~ 19 picture elements (live viewing) to represent the width of a persons head.

If the image is recorded on a VHS VCR and replayed the situation will be considerably worse, VHS resolution is ~ 320 horizontal lines, this equates to ~ 13 horizontal picture elements to represent the width of a persons head. If a Super-VHS recorder is used (~ 530 horizontal lines) resolution will be similar to live viewing. When viewing video taped images quality will be poorer (than live viewing) due to tape signal-to-noise ratio and other recording limitations.

In a common shop or showroom situation a reasonable compromise may be to use a fairly narrow angle lens on a camera monitoring the entrance, together with other cameras with wider angle lenses to give an overview of other areas.

MONOCHROME:
Use an Automatic Iris Lens and an Infra-Red 'Cut' Filter with 'Automatic Electronic Shutter' (AES) Off, this will ensure SHARPEST FOCUS, BEST RESOLUTION & COLOUR-GREY CONVERSION.

COLOUR:
If  used outdoors, in brightly lit areas or areas where illumination varies considerably, use an Automatic Iris Lens with AES Off.

Smear is a CCD Sensor characteristic, strong light entering the CCD sensor will penetrate the photo sensitive layer and create lag. This unwanted image is called smear and becomes more evident as shutter speed increases, the extent that a CCD Sensor can reject strong light is called the Smear Rejection Ratio. See: GEM-II for pictorial representation of 'Smear'.

Dynamic range is the range between the darkest and the brightest areas of a scene that a camera can cope with and still produce a correctly exposed image with correct colour rendition. Ordinary colour cameras normally have an approximately 3:1 linear dynamic range that is limited by the saturation of Cyan Magenta Yellow and Green filter at 450 mV and a minimum signal level of 150 mV (450 mV : 150 mV = 3:1 ). See: GEM-II for pictorial representation of 'Dynamic Range'.

Higher quality cameras may achieve a wider range with a better CCD, Digital Signal Processing and a special RGB mosaic conversion algorithm, these may achieve 750 mV saturation on Red colour and a minimum signal level of 100 mV = 7:1 dynamic range (750 mV : 100 mV) 2.5 times better than ordinary cameras.

An even more dramatic increase in Dynamic Range can be achieved by using a Double Speed CCD, Digital Signal Processing & Digital Memory.

Most ordinary CCTV cameras have a SNR of from 40 ~ 48 dB, better cameras may have an SNR as high as 60 + dB. The SNR figure quoted in camera specifications is usually as measured with the camera's AGC (Automatic Gain Control) off.

At normal to high illumination levels the AGC gain will be quite low, possibly unity (1), therefore the effects of SNR will be less obvious (unless the SNR is very low). At lower illumination levels the AGC gain will increase raising the video signal level, however the noise is also raised and the effect of noise on the image becomes more noticeable (similar to noise on a TV image in low signal conditions).

A cctv camera with a high SNR will produce cleaner images with less noise under all conditions, SNR is an even more important consideration as Digital Video Recording and Transmission (LAN, WAN, Modem, WWW, Telephone Line) becomes more commonplace. With a high SNR compressed file sizes will be smaller and throughput higher, this is because noise which is interpreted as image changes (more data) increases file size.

Blemish is latent imperfections in the photodiodes (pixels) in an Image Sensor, one or more of the several hundred thousand pixels in a sensor may be imperfect resulting in a constant or fluctuating White, Coloured or Dark dot. In common well lit Home, Shop, Showroom, Office, Warehouse type surveillance situations a single pixel is usually imperceptible.

Our Low Blemish cctv cameras are fitted with Image Sensors that typically have 0 ~ 10 imperfect pixels that are usually located outside of the more important central area of the sensor.

While most imperfect pixels are evident during inspection following manufacture of the Image Sensor Chip it is normal for pixels in some specialised high sensitivity Image Sensors (EXview, HAD, Day/Night) to fail during storage, after installation in a CCTV Camera and after delivery to the end user, this process will continue until the latent defects in the photodiodes stabilise.

It is normal for some pixels to fail as part of the normal aging process during the lifetime of a cctv camera.

(Picture elements = Pixels)

Colour Day Night CCTV Cameras with inbuilt Infrared Light Emitting Diodes "See-in-the-Dark" and produce images when visible illumination is zero.

At average levels of illumination these CCTV Cameras produce Colour images, depending on their sensitivity (Lux) at low illumination levels and in total darkness the image is Monochrome.

These CCTV Cameras generally have a relatively high sensitivity image sensor and Fixed Iris Lens therefore under high illumination levels images will be overexposed for the reasons outlined here, an exception is MINI-COL-IR which has a special Wide Dynamic Range allowing it to cope with higher illumination levels than ordinary CCTV Cameras.

Ordinary Colour CCTV Cameras are relatively insensitive to Infrared because they have an IR CUT Filter between the Lens and Image Sensor, this filter excludes Infrared radiation with a wavelength greater than ~ 700 nm that would otherwise adversely affect White Balance, Colour Rendition and Image Sharpness.

Day / Night Colour CCTV Cameras are sensitive to Infrared because they either do not have an IR CUT Filter or utilise a special NOTCH IR CUT Filter that excludes the wavelengths most harmful to colour quality (720 ~ 830 nm) from reaching the Image Sensor.

A Colour CCTV Camera that does not have an IR CUT Filter usually has poor colour rendition characterised by a Pink-Red 'tint' when the illumination is InfraRed rich, use of a 'Notch' Filter helps however White Balance, Colour Rendition and Image Sharpness are compromised for Infrared sensitivity. (Image Sharpness can be restored by using a specially designed Lens that corrects the focus shift between Visible and Infrared)

The IDEAL Day / Night Infrared Sensitive Colour CCTV Camera would utilise an Automatic Iris Lens to cope with high illumination levels and the Lens would also have a large aperture (low 'F' number) to maximise light transmission when illumination levels are low * it would also utilise a Traditional IR CUT Filter when illumination levels are adequate for Colour and then REMOVE the IR CUT Filter when levels are low Dome-DayNite, Maxi-DayNite, Dome-D/NiteEx, Maxi-D/NiteEx & CCS-IRdnWD have these features and are recommended for OPTIMUM results - the ULTIMATE SOLUTION is AutoCam-dn or DomePTZ-dn these also have Automatic-Focus to ensure crisp images under all conditions.

Infrared rich light sources include Daylight and most Filament type lamps including common Spot lamps, Tungsten lamps, Halogen lamps, etc.

The majority of Light emitted from 'Cold' type sources such as Fluorescent, Mercury Vapour, Sodium Vapour, etc., is visible, these sources contain little Infrared energy.

SUMMARY: "See-in-the-Dark" Infrared capability is a trade-off that affects Colour Quality particularly in "Infrared Rich" environments.

CCIR = Australian / UK / European Monochrome TV System
PAL = Australian / UK / European Colour TV System
EIA = USA / Japan Monochrome TV System
NTSC = USA / Japan Color TV System
SECAM = France / Russia TV System

!! IMPORTANT note about  TV Systems !!

Although the CCIR/PAL cctv cameras we stock are incompatible with USA / Japan TVs and VCRs they can be used with most of Digital Video Recording Systems for HIGHER RESOLUTION IMAGES than possible with EIA/NTSC cctv cameras.

Are based on information and data supplied by manufacturers.

Due to continual product development and improvement specifications may change.

Additional information and data may be available for some items, if you require additional information, in your request please specify the parameters you require.

All care has been taken to ensure accuracy of specifications etc., however we accept no responsibility for errors or omissions.

Cable Data (for reference purposes)

VIDEO

RG-179BU, ~ 2.54 mm Ø, ~ 17 dB attenuation/100m @ 10 MHz.
RG-59BU, ~ 6.15 mm Ø, ~ 3.5 dB attenuation/100m @ 10 MHz.
RG-6/U, ~ 7 mm Ø, ~ 2.3 dB attenuation/100m @ 10 MHz.
RG-11/U, ~ 10.3 mm Ø, ~ 1.2 dB attenuation/100m @ 10 MHz.

For connecting Standard 75 ohm 1 v p-p CCIR & PAL Composite Video Signals between CCTV Cameras, Quads, Switchers, Monitors, etc.

RF

RG-223, ~ 5 mm Ø, ~ 16.7 dB attenuation / 30 metres @ 3 GHz.
CS23, ~ 5 mm Ø, ~ 22.5 dB attenuation / 30 metres @ 2 GHz.
RG-142, ~ 4.5 mm Ø, ~ 27 dB attenuation / 30 metres @ 3 GHz
RG-58, ~ 5 mm Ø, ~ 54 dB attenuation / 30 metres @ 3 GHz
RG-316, ~ 3 mm Ø, ~ 60 dB attenuation / 30 metres @ 3 GHz
RG-178, ~ 1.75 mm Ø, ~ 76 dB attenuation / 30 metres @ 3 GHz

For connecting 2.4 GHz Antennas, Transmitters & Receivers

A low attenuation figure is best, above data is typical, actual characteristics will depend on manufacturer & cable grade/quality.