20/20 Vision From Your Surveillance Camera Lens!

If you ever want to attain an instant headache, look through someone else’s prescription eyeglasses or attach the wrong type lens to your surveillance camera.

This article is to help you see things normally.  Optics are a vital aspect to the efficiency of a video surveillance system, and in the great scheme of things, possibly the least well understood aspect of video surveillance work.

In our industry of video surveillance, all surveillance cameras face a similar challenge. The image sensor of a camera is much like an eye, and the lens serves the same role as a pair of prescription glasses.  For your camera to attain perfect  20/20 vision, it needs to be fitted with the right CCTV lens for the job.

Lens basics have not changed much over the years.

1.     You still need to choose a lens mount

2.     Determine the appropriate focal length

3.     Match the lens to the surveillance environment — whether indoors or outdoors

But with some of the newer network camera technologies, such as megapixel and HDTV resolution, lens selection becomes even more critical for optimum performance. The following are some of the key issues you need to consider when seeking the right lens for your surveillance application.

Matching Lens to Sensor

A camera "sees" when light passes through a lens and is then focused on the camera’s image sensor. The image sensor is made up of many tiny photosites, and each photosite corresponds to a picture element, more commonly known as a "pixel." Each pixel on an image sensor registers the amount of light it is exposed to and converts that light into a corresponding number of electrons. The brighter the light, the more electrons are generated.

Image sensors come in a range of sizes, most commonly one-quarter to one-third of an inch — so you need to make sure to choose the right sized lens for the sensor. If the lens is rated for a smaller image sensor than the one inside the camera, the field of view will have black corners. Conversely, if the lens is rated for a larger image sensor than the one inside the camera, you will lose some of the field of view outside the image sensor range. 

This situation creates a telephoto effect, making everything look zoomed in.

**An example of telephoto effect can be seen in this photograph “San Francisco” where the Golden Gate Bridge and city skyline are actually miles from each other.

In the case of a megapixel or HDTV camera, you need a high-quality lens, since these sensors have pixels that are much smaller than those on a VGA sensor. The pixels must be smaller in order to fit that many more on the sensor. For instance, a 720p camera with 1280 x 720 pixels has three times as many pixels as a VGA camera, which has 640 x 480 pixels. To fully use the camera’s capability, the lens and camera resolutions should match.

Picking the Right Lens Mount

Network cameras use one of two standard mounts: CS-mount and C-mount. They both have 1-inch thread and look the same. Where they differ is in the distance from the lens to the sensor when fitted on the camera. If you find it impossible to focus the camera, it is likely that you attached the wrong type of lens mount.

In a CS-mount, the most common lens mount, the distance between the sensor and the lens should be 12.5 mm; in a C-mount, the distance between the sensor and the lens should be 17.526 mm.

Choosing the Right Focal Length

A lens’ focal length is defined as the distance between the entrance of light into the lens and the point where the light rays converge on the image sensor. The general rule is that the longer the focal length, the narrower the field of view. There are three types of fields of view:

• Normal — a view that most closely corresponds to how the human eye sees;
• Telephoto — a narrower field of view that generally provides finer details than can be detected by the human eye; and
• Wide angle — a larger field of view with less detail than seen by the human eye.

Correspondingly, there are also three main types of lenses:

• Fixed only provides one type of field of view (normal, telephoto OR wide angle).
• Varifocal offers a range of focal lengths and different manually adjustable fields of view. Whenever you change the field of view, you need to manually refocus the lens. Remote focusing capabilities have been added to the latest generation of network cameras, enabling you to focus the camera from a remotely-located computer instead of while up on a ladder or lift.
• Zoom offers a range of focal lengths and different adjustable fields of view. Unlike varifocal lenses, zoom lenses do not require refocus of the lens if you change the field of view. They automatically maintain focus within a range of focal lengths, such as 6 mm to 48 mm. You can adjust zoom lenses manually or remotely through motorized control.

Deciding on an Iris Control

Another important factor in image quality is how you control a camera’s iris opening. The iris — which lets in a specific amount of light depending on the size of its opening — controls the depth of field and maintains the optimum light level to the image sensor so that the image appears sharp, clear and correctly exposed with good contrast and resolution. Iris control can be fixed or adjustable.

• Manual control allows you to adjust the iris opening by turning a ring on the lens. Like a fixed control, it works best where light levels are constant.
• DC-iris, also known as auto-iris control, uses the camera’s processor to automatically adjust the aperture (opening of the iris) to changing light conditions. The DC-iris only has two aperture settings — small and large. It cannot be fine-tuned to an exact iris position.
• P-iris control provides an automatic, more precise aperture as it uses special software to communicate with and control the iris’ exact position to manage even the slightest change in light. This provides better, “precise” control to optimize contrast, clarity, resolution and depth of field. The P-iris control also eliminates the blurring problems that may occur with DC-iris control, which is especially important in high-resolution cameras such as 3- and 5-megapixel.

Choosing the Right Resolution

Different surveillance objectives require different resolutions, so you need to select a camera and lens that match the field of view to the size of the scene you want to capture. If your only goal is to detect an individual in a scene, a lens with a linear resolution of 20 pixels per meter would probably be sufficient. For forensic detail such as a license plate number, the linear resolution would need to be around 200 pixels per meter. For facial identification purposes, the resolution would have to be closer to 500 pixels per meter.
Check that the megapixel rating for the lens matches the megapixel rating of the camera. Image quality suffers when you use a non-megapixel rated lens on a megapixel camera or even a lower-resolution megapixel lens on a higher-resolution megapixel camera.

Compensating for Infrared Lighting

Lenses often experience color distortion called chromatic aberration. 

This occurs because lenses have different refractive indices for different wavelengths of light and every color in the optical spectrum cannot be focused on a single common point. The aberration often manifests itself as fringes of color along boundaries that separate dark and bright parts of the image. Choosing an achromatic lens — a compound of different materials with differing light dispersions — reduces the amount of chromatic aberration over a certain range of wavelengths, though it does not eliminate the distortion altogether.

If you are using a day/night camera, be sure the lens includes an IR cut filter on the lens that can be automatically or manually removed depending on lighting conditions. That way, when surveillance occurs under infrared lighting conditions, the lens will not trigger a shift in focus and color distortion.

Specialty Lenses

Specialty lenses compensate for a host of problems. For instance, a wide-angle, low barrel distortion lens offsets barrel distortion caused by lens magnification being smaller at the edges of the field of view compared to the center of the image. This phenomenon is often more pronounced at short focal lengths, making a standard wide-angle lens less suited for identification purposes.

Motorized optical and digital zoom lenses with auto focus enable remote manipulation the camera, zooming in on small or distant objects with exceptional clarity. When the camera faces direct sunlight, putting a polarized light filter can improve the camera’s light sensitivity and image quality.

Final Recommendations

As with any technology, the science of camera lens-making continues to make advances — though nowhere close to the rapid pace of improvements in semi-conductors and image processors. Like all leading-edge improvements, pricing will fluctuate depending on the quality of the lens and the features it includes. For instance, a low-cost fixed iris lens could be found for as low as $10, while a varifocal P-iris lens for a 5 megapixel camera could cost several hundred dollars, and a zoom lens even more.

Comparable to professional SLR still photography cameras, the lens is often the surveillance camera’s most expensive component. Often, buying a camera with the lens included provides optimum price performance — so shop wisely. Compare costs and features across multiple manufacturers to make sure the type of lens you choose is the perfect fit for you.

Florida School Board Meeting Shooting - Full WMBB Video - December 14, 2010

(CNN) -- Clay Duke sat quietly through the first portion of the Bay District Schools, Florida, school board meeting Tuesday afternoon as local children were honored for their achievements.

When it came time for citizens to bring up issues, the 56-year-old resident calmly approached the front.

He spray painted a red "V" with a circle around it on the wall, brandished a small-caliber handgun and ordered the room cleared at a Panama City schools building.

"Six men stay. Everyone else leave," the burly gunman said.

Moments later, Ginger Littleton, a board member, returned to the room and swung a purse at him. She ended up on the ground after the two struggled. The gunman cursed her, but did not open fire and he let her leave the room.

Someone was going to die, he said.

The confrontation ended in the gunman identified as Duke calmly firing at the school officials, being wounded and, according to police, taking his own life.At that point, Duke, as seen on the dramatic live internet feed provided by CNN affiliates WJHG and WMBB, began a rambling discourse that included the apparent firing of his wife and sales taxes.

At first, school board members and Superintendent Bill Husfelt tried to reason with Duke, who had a criminal record. They talked about possibly finding a job for Duke's wife or looking into the case.

Husfelt told the gunman that he likely signed the termination papers, but didn't recall the circumstances.

"I'm the one who signed the papers," Husfelt. "Let them go," he said referring to the school board members.

At one point, Husfelt said, "I don't want anybody to get hurt. I've got a feeling that what you want, is you want the cops to come in and kill you because you are mad. Because you said you are going to die."

"But why? This isn't worth it," the superintendent told him. "This is a problem."

The gunman then pointed the pistol at the official.

"Please don't. Please don't. Please," Husfelt said.

The gunman opened fire at Husfelt and school board members. He missed them all, even though he was at close range, said Lee Stafford, director of student services of Bay District Schools. Duke said, "I'm going to kill [unintelligible]," while he fired.

Mike Jones, chief of security for the school system and a retired police officer, exchanged fire with Duke, who was wounded and rolled to the ground. Duke turned his gun on himself, dying of a fatal gunshot to the head, authorities said. Husfelt called Jones a "hero."

The gunman was declared dead at a local hospital. An autopsy is expected Wednesday.

Police and school officials were left to piece together what happened.

"I'm sure they never expected this kind of event to occur," Sgt. Jeffrey Becker of the Panama City Police Department.

The superintendent later related the event as being "surreal," Becker said.

Husfelt told reporters that Duke had almost a smile on his face. "He made up his mind. You could tell he was going to die."

The superintendent said he believes the gunman used a combination of live bullets and blanks. But police said live bullets were used.

Husfelt told "AC360" Tuesday night that the gunman was "just mixed up" and that he tried to calm him down. "I knew the police were on their way."

"You knew he had something in mind he was going to do and it would not end well," Husfelt said.

The superintendent said he wanted to protect the school board members, but Duke did not want to talk.

"The good Lord was standing in front of me," said the school chief, adding authorities found two bullet holes behind his desk.

Police have a solid lead on Duke's motive, Becker said, but were not prepared Tuesday night to release it.

The investigation includes Duke's assertions that his wife had been terminated by the school district. Police were talking with Duke's wife, Becker said.

School officials said they were unaware of the significance of the spray painting.

But a Facebook page belonging to a Clay Duke has a profile photo of a "V" in a red circle, a logo that is used in the movie "V for Vendetta."

According to the Internet Movie Database, the 2006 film is about "a shadowy freedom fighter known only as "V" uses terrorist tactics to fight against his totalitarian society. Upon rescuing a girl from the secret police, he also finds his best chance at having an ally."

CNN could not verify if the Facebook page belonged to the gunman, but it does list Duke, 56, as living in Panama City, Florida.

A biography on Duke's Facebook page reads: "My Testament: Some people (the government sponsored media) will say I was evil, a monster (V)... no... I was just born poor in a country where the Wealthy manipulate, use, abuse, and economically enslave 95% of the population. Rich Republicans, Rich Democrats... same-same... rich... they take turns fleecing us... our few dollars... pyramiding the wealth for themselves. The 95%... the us, in US of A, are the neo slaves of the Global South. Our Masters, the Wealthy, do, as they like to us..."

Under "political views," Duke labels himself a "Freedom Fighter." Under religious views, he wrote, "Humanism."

Duke, who lived in Lynn Haven, a suburb of Panama City, has a previous record, Becker told CNN.

According to the website of the Florida Department of Corrections, Duke was sentenced in 2000 for aggravated stalking, obstructing justice and throwing or shooting into a vehicle.

According to the Panama City News Herald, after six months of stalking a former girlfriend, Duke confronted the woman outside her home on Oct. 20, 1999. He was wearing the mask and vest and holding two .22-caliber guns. He threatened to kill her, then kill several others and then himself, the newspaper said. When the woman tried to drive away, Duke shot out a rear tire.

The photo of Duke on the corrections page matches the Facebook page.

The News Herald reported that the gunman was taken out of the building on a stretcher. According to Panama City Police Chief John Van Etten, no one other than the suspect was injured, affiliate WJHG said.

School board spokeswoman Karen Tucker said the man "was a large guy" she had seen sitting in the back of the boardroom earlier, according to the News Herald.

Superintendent Husfelt will hold a press conference at 9:30 a.m. Wednesday at the administration building in Panama City, police said.

CNN affiliate WMBB reported children and parents were at the meeting to be recognized for achievements, but were gone before the incident began.

"We are absolutely in state of shock," said Stafford. "I was in the third floor and we were watching the live feed, and first we thought it was a drill. But the more that you watched it, we realized this was an actual incident and emergency situation."

Duke's Facebook page listed him as a 1972 graduate of King High School in Tampa.

His favorite quotation: "You want the truth? You can't handle the truth," from the movie "A Few Good Men."

Bugged By CCTV Cameras?

CCTV cameras that detect potential offenders and then "tail" them are being tested in British shopping centres.

The $14,000 "Bug" is fitted with a ring of eight cameras that gives a panoramic view of a street.

The footage is scanned by sophisticated software which can identify 50 behavior traits that indicate whether somebody is acting or loitering in a suspicious manner.

When a suspect is spotted, a ninth camera automatically locks onto them and follows their movements.

It means town centres can be monitored without the need for human operators to watch screens.

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The device has been tested in Europe for the last 18 months and are due to install the "intelligent" camera system.

Jason Butler, head of CCTV at Luton council, said: "The camera picks up on unusual movement, zooms in on someone and gathers evidence from a face and clothing, acting as a 24-hour operator without someone having to be there.

"We have kids with Asbos telling us they hate the thing because it follows them wherever they go."

But civil liberty campaigners claim the cameras are yet another extension of state surveillance in what is already the world's most spied upon country.

There are 4.2 million CCTV cameras in Britain - a fifth of the world's total.

Earlier this month the Home Office announced plans to extend the use talking CCTV cameras that order passers-by to pick up dropped litter.

Critics say the Bug sounds like a step towards the world depicted in the 2002 science fiction film Minority Report, where Tom Cruise stars as an officer in a police "department of pre-crime" that arrests offenders on the basis of what they are about to do.

Simon Davies, director of Privacy International, said: "We do not know what the psychological impact of this will be on the population."

But Stuart Thompson, managing director of Kent based company Viseum that developed the Bug, said the innocent had nothing to fear from the device.

He said: "It may mistake someone window-shopping for someone loitering, but on every occasion that a crime has been committed the system has always caught evidence."

Several police forces are also considering another intelligent camera attached to unmanned drones that fly stealthily above cities to spy on people below.

The camera can zoom in on and track a single face from 500 feet.

These can then be scanned and matched against a database of known criminals or terror suspects. The camera is fitted to a drone made from lightweight plastics and carbon fibre called the Casper 250, which was originally created for the Israeli army.

It has a wingspan of 8ft and a top speed of more than 50mph, but is powered by an electric engine, making it almost inaudible to those on the ground.

Police believe it could be used to help routine work such as monitoring traffic, demonstrations and marches, and for more sensitive operations such as tracking drug traffickers and terrorists.