A speed dome — or PTZ, from the initials for pan, tilt, and zoom — is a camera that rotates on its axis, tilts, and zooms in with a motorized lens. Seeing one in action is quite impressive, and that is part of the problem: people buy more speed domes than they actually need.
The flaw no one tells you about
A motorized camera looks in only one direction at a time. While it is pointed at the gate, it isn't watching the back. If someone enters from the back while the camera is turned away, that event doesn't exist anywhere: it's not that you recorded it poorly, you didn't record it at all.
Fixed cameras have the opposite flaw, and for surveillance, it's a better one: they always see only their slice of the world, but they see it twenty-four hours a day. That is why the rule we follow is: coverage is provided by fixed cameras, with a speed dome added on top, never as a replacement.
When it actually makes sense
There are four situations in which a PTZ is worth the price.
Very large areas with few points of interest. A ten-thousand-square-meter yard: covering it entirely with fixed cameras would mean twelve cameras; four fixed ones at the gates plus a PTZ patrolling the center do a better job for less money.
Someone is watching. In a guarded facility — a porter's lodge, a guard room, a control center — the operator uses the PTZ like binoculars: pointing it where needed, zooming in, reading a license plate. Without someone watching, this capability is never used.
You need to read something far away. A license plate at eighty meters, a container number, the face of someone ringing the bell at the gate of a villa with a long driveway. This is the only case where optical zoom is irreplaceable: a 4K fixed camera that enlarges digitally yields pixelated blocks, while a PTZ with 25x zoom yields readable characters.
The perimeter needs to be patrolled for deterrence. A visibly moving camera signals that the facility is alive. In certain sites, that counts for more than the recording.
What to look for on the spec sheet, and in what order
The most important number is the optical zoom, which should not be confused with digital zoom. 4x is low and only useful for adjusting the frame. 15x is the useful range for a courtyard or yard. 25x can read a license plate at seventy to eighty meters. 32x and above are for ports, quarries, and large perimeters.
Then the infrared range, because a PTZ that zooms at night needs to illuminate what it is capturing: serious models have infrared that focuses along with the zoom, reaching 100-200 meters. A model with 25x zoom and 30-meter infrared is a daytime tool in disguise.
Then the presets: stored positions to which the camera returns via a command or automatically. They are the foundation of everything else. Presets are used to build a patrol tour, which is a cyclical route between positions, with a pause of a few seconds at each.
Finally, auto-tracking: the camera locks onto moving subjects and follows them. It works well in clean, empty areas, like a yard at night. It works poorly where movement is continuous: a busy road confuses it, and the camera ends up spending the day chasing cars. Before enabling it, watch what moves in that frame on a normal day.
The power bill
A PTZ is not powered like a fixed camera. The motors consume power during movement, the heater kicks in below five degrees, and the long-range infrared draws power: you can easily reach 30 to 60 W. It requires a dedicated Hi-PoE port, 802.3bt standard, or local 12V or 24V power supply. Attaching one to a standard PoE+ switch, along with six other cameras, is the classic way to find ports shutting down at night without knowing why.
The honest calculation
A mid-range speed dome costs as much as four or five good fixed cameras. Before buying one, ask yourself this question: with four extra fixed cameras, would I cover everything the PTZ would cover in rotation? If the answer is yes, get the fixed cameras. If the answer is no because the area is too large, or because you need to read something far away, then the PTZ is the right choice and the money is well spent.
In our catalog, you can find Uniview speed domes, X-Security speed domes, and Safire Smart speed domes, ranging from 4x to 32x zoom. For power supplies, check out our power adapters and, if you are in doubt about which model can support your system, write to us at info@elettricity.com.