360 degrees of protection with the dome security camera

360 degrees of protection with the dome security camera

Pan/Tilt/Zoom cameras or PTZ cameras or 360degree cameras remain critical parts of many surveillance systems, especially in large security operations. Because of this it is important to understand and consider the key elements in selecting and using PTZ cameras.

In this guide we cover the basics of PTZ cameras and their selection, including:

• Pan/tilt/zoom basic terms
• Zoom ratios explained
• Using angle of view instead of zoom rating
• E-flip examined
• Available PTZ resolutions and their advantages/disadvantages
• Form factor selection (speeddomes, mini PTZs, positioners)
• Integrated IR PTZs
• PTZ lens issues
• Actual versus effective PPF
• Presets and tours
• Common applications

Pan/Tilt/Zoom Camera Basics

PTZs combine a camera with a motorized mechanism which allows it to move in multiple directions. These movements are referred to as:

• Pan: Left/right horizontal movement
• Tilt: Up/down vertical movement
• Zoom: Near and far 

This example demonstrates each of these movements:

Note that the extent to which cameras may be moved varies. Some models may be limited to 340° panning, some may tilt above horizontal, and zoom levels may vary from only slight magnification to extremely long distance. These specs depend on the type of PTZ (detailed below) and individual manufacturer/model.

E-Flip

Many PTZs include a feature called "E-flip" which automatically rotates the camera 180° when the operator is following a subject directly beneath it. This is a more intuitive control method than models which do not include E-flip, as the user must manually rotate the camera to follow the subject as they pass below.

This example shows the camera flipping as it is tilted down to 0° and beyond, while only the down tilt control is pressed.

Zoom Ratio

Manufacturers most often advertise PTZs using their optical zoom ratio, e.g., 18x, 26x, 36x, etc. This ratio is formed simply by dividing the camera's maximum focal length by its minimum, such as:

Use View Angle Instead

However, using only zoom ratio as an indicator of PTZ zoom performance misses some key details. Since lenses have differing wide/telephoto focal lengths, two cameras with the same ratio may have very different fields of view.

For example, looking at the specs of two 18x zoom cameras, we can see that one has a telephoto angle of view ~30% narrower (and thus higher PPF) than the other due to varying lens specs. But the reverse is also true, with the camera on the right having a wider possible angle of view, which may be more useful in some applications.

Users must beware of these issues when selecting PTZs and choose based on their required areas of interest. 

Ignore Digital Zoom

Some PTZ models include digital zoom in addition to optical, even in some cases  multiplying the two to create a deceptive "total zoom" figure, such as this camera:

However, digital zoom is a "fake" zoom, not providing additional details, only enlarging pixels captured and these specs should effectively be ignored in favor of angle of view as discussed above.

Resolutions Available

PTZs are now available in varying HD resolutions, as well as standard definition. Historically, zoom lenses for megapixel cameras were not available, though in the past few years, 1080p PTZs with 36x zoom have become readily available.

Note that HD is not necessarily preferable in PTZ applications, due to flaws in long focal length megapixel lenses, detailed later in this report.

PTZ Form Factors

There are three typical types of PTZ camera in use today, with different strengths and weaknesses, overviewed in this chart and detailed below:

Speeddome

The most common type of PTZ in use is the speeddome, which packages the camera/lens and pan/tilt mechanism in a dome form factor, typically 8-10" in diameter.

Speeddomes have several advantages:

• Pre-packaged: Due to their construction, speeddomes typically require less work to mount than positioning systems (below), and may be mounted in a variety of locations. Wall, pendant, recessed ceiling, and other mounts are all readily available.
• Integrated IR available: Several manufacturers now offer speeddomes with integrated IR (detailed further below), which greatly improves their usefulness in low light, as speeddomes historically have used relatively high F-Stop lenses, poor in dark scenes.
• Fast PTZ speeds: Speeddomes are the fastest movable cameras available. Speeds over 300º per second are not uncommon, and over 400º per second is not unheard of. This allows tracking of faster-moving subjects, and shorter movement times when switching between presets, often a fraction of a second.
• Pan/tilt range: Speeddomes typically feature full 360º pan range, without stops, and 180º tilt range with e-flip, to allow trailing of subjects as they move beneath the camera. Many cameras have extended tilt beyond 90º, with some offering up to 15º of up-tilt, above the horizon. Up-tilt previously required a pan/tilt positioner.
• Less wind loading: Compared to pan/tilt positioning systems, reviewed below, speeddomes do not have as many issues in strong winds, which may cause vibration in pan/tilt cameras.

Mini PTZ

Mini PTZ domes are a relatively recent development, with several manufacturers now offering models. These smaller PTZs have two key advantages:

• Low cost: Mini PTZs are must less expensive than full size speeddomes, often ~$300 USD or less, compared to $800-2000 for a speeddome.
• Small size: These models are much smaller than typical speeddomes, close to the size of a typical fixed dome camera (5-6" diameter) and much smaller in height.

However, there are disadvantages to mini PTZs as well:

• Limited zoom: Mini PTZs are typically limited to low optical zoom ratios such as 3x, though some may be found up to ~10x. Compared to other PTZs, often 30x or more, this is very low.
• Limited positioning range: Mini PTZs typically do not include full 360° panning, nor e-flip found in speeddomes.
• Slow pan/tilt speed: Panning speed of a mini PTZ is typically very low, 30-90 degrees per second, a fraction of speeddome panning speed.

Pan/Tilt Positioners

Pan/tilt positioners are the oldest type of movable camera system, available prior to integrated PTZ speeddomes. These systems historically consisted of separate componentes which were manually integrated: the positioner itself, a separate camera, and zoom lens. 

However, some manufacturers now offer pre-packaged IP positioning systems, such as the Axis Q86/Q87 and Pelco Esprit.

The key advantage to pan/tilt positioners is flexibility. Users may choose from multiple cameras and zoom lenses, instead of being limited to available speeddome options. This is useful when extremely long-range zoom lenses are required, as lenses over 100x zoom are available.

Positioners were previously the only option when infrared illuminators were desired in a PTZ camera. However, speeddomes with integrated IR have now largely caught up, offering long range infrared.

There are two key drawbacks to positioners:

• PTZ speed: Positioners often have low pan/tilt speeds, due to the weight and balance of cameras mounted on them. Increasing speeds could lead to increased vibration and "bounce" as cameras started and stopped moving, making tracking more difficult.
• Wind loading: Due to their increased profile, positioning systems in exposed areas may suffer from vibration due to wind, which is reduced or not present when using speeddomes.

Integrated IR Speeddomes

One recent advance in PTZ speeddomes is the addition of integrated IR, previously mainly found in positioners only. Many manufacturers now offer integrated IR speeddomes, such as Bosch, Dahua, Hikvision, and Samsung.

Integrated IR speeddomes have outperformed non-IR models in our tests at all ranges, with illumination at 450' and beyond. For example, the comparison below shows a 1080p IR PTZ versus a non-IR model at ~485' distance, with the subject clearly displayed in the IR model. The non-IR PTZ displays only noise, no usable image.

PTZ Lens Issues

When planning PTZ camera use, users should be aware that PTZ and other long focal length lenses do not resolve images the same as shorter focal length lenses, resulting in a reduction in practical details delivered. Because of this, when calculating needed PPF using PTZ cameras, users should expect a ~50% or higher reduction in delivered details.

For example, the image below shows a subject at ~420' using a 1080p camera, in an 87 PPF scene. However, details delivered are similar to ~35-40 PPF, less than half of actual.

Note that SD PTZs do not suffer typically suffer from these effects. For example, the VGA PTZ below displays a better image than the 1080p model at the same range, despite its much lower actual PPF.

PTZ Presets and Tours

In order to make PTZ operation easier, these cameras include the option to define predetermined positions, called "presets", which may be used to quickly move the camera to a specific position. For example, the clip below shows several presets covering a parking lot, quickly called in succession using a VMS.

In addition to presets, PTZs include tours (also called patterns) which move the camera automatically on a preset time schedule (typically every 3-10 seconds). Tours in current cameras most often call presets in a specific order (called a preset tour).

However, in the past, tours were typically defined by recording an operator manually moving the camera. This style of tour has generally fallen out of favor, though, as it becomes more difficult to spot small objects in motion as the camera is moving, and the constant PTZ movement precludes the use of camera-side video motion detection, which may be used in preset tours.

Most Common PTZ Applications

For the most part, PTZ usage is dropping in favor of fixed megapixel cameras, but there are still applications in which they are frequently used.

• Live monitoring operations: In systems with surveillance operators, PTZs are still often used, as they allow the user to more closely inspect and follow subjects than is possible with fixed cameras. Live monitoring is most often used in larger, higher security systerms, such as airports, critical infrastructure, city surveillance, etc., though many large retailers also employ PTZs and operators.
• Large areas: In very large areas, PTZs on preset patterns are still sometimes used instead of fixed megapixel cameras due to the higher details they may deliver at long range. For example, the image below compares 4K and 5MP cameras against HD and SD PTZs, with even the lowest resolution PTZ delivering details of the subject at this range: