Dome CCTV Camera Field of View and Technical Specifications

Dome camera optics: housing, bubble, IR cut

Every dome camera is an imaging stack of five elements: the dome bubble, the IR-cut filter, the lens assembly, the image sensor, and the IR LED ring. The bubble is the only element unique to the dome form factor, and it is the dominant source of FOV degradation if specified or maintained incorrectly. Standard bubbles are 2-3 mm thick acrylic (PMMA) or polycarbonate (PC). Acrylic offers better optical clarity (light transmission ~92%) and scratch resistance; polycarbonate trades a few percent of transmission for far higher impact resistance and is mandatory for IK10-rated vandal domes.

Clear vs tinted (smoked) bubbles. Clear bubbles preserve full light throughput and IR transmission, giving the best low-light and night-vision performance. Tinted bubbles — usually called "smoked" or "black bubble" domes — hide the aim direction visually but cut visible light by 30-50% and IR by 10-20%. A tinted bubble can drop a camera's effective IR reach from 30 m to 18-20 m. Use tinted only where covert aim direction is more valuable than night performance (luxury retail, hotel lobbies); never on perimeter or low-light scenes.

Corner distortion. The bubble is a spherical section. When the camera tilts toward the bubble edge, the line of sight passes through the acrylic at an oblique angle, refracting the light path and introducing 1-3% barrel distortion plus minor chromatic aberration at the frame corners. This is invisible at mild tilt angles (under 30° from vertical) but becomes pronounced past 60° tilt, where the image edge can lose 5-8% of effective resolution. Lens manufacturers correct most of this with computational profiles, but the effect is real on wide-angle SKUs.

IR bounce and the dirty-dome problem. The IR LED ring sits inside the bubble, just outside the lens barrel. If the bubble surface accumulates dust, fingerprints or scratches, IR light reflects off those imperfections back into the lens, producing a glowing white spot in the centre of the night-time image. This is the most common cause of "blind at night" complaints in dome installations. Cleaning the bubble with a microfibre cloth restores performance; deeply scratched bubbles must be replaced. Higher-end domes (Axis Q35, Hikvision DarkFighter, Dahua Lite AI) use a foam light gasket between the lens barrel and the bubble to block this internal reflection — check the spec sheet for "IR baffle" or "light isolation".

Vandal vs non-vandal housings. A non-vandal indoor dome typically uses 1.5-2 mm acrylic and a plastic base ring (IK04-IK06). A vandal-rated dome uses 3-4 mm polycarbonate, a die-cast aluminium base, tamper-resistant screws, and is tested to IK10 (50 J impact). The vandal housing weighs 600-1200 g versus 200-400 g for indoor, which matters for ceiling-tile installations where a back-box brace is required above 700 g.

Dome FOV by focal length: 2.8 / 4 / 6 / 8 / 12 mm chart

The horizontal field of view of a dome depends on two values: focal length and sensor diagonal. The formula is HFOV = 2 · arctan(sensor_width / (2 · focal_length)). The table below gives horizontal and vertical FOV for the five most common focal lengths on three modern sensor sizes. Numbers are typical manufacturer specifications, rounded to the nearest degree; individual SKUs vary by ±2°.

Notice that moving from a 1/3" to a 1/2" sensor at the same focal length widens HFOV by roughly 25%. This is why higher-end domes with 1/1.8" sensors quote noticeably wider angles than budget 1/3" units even when both spec a 2.8 mm lens. For precise per-SKU numbers, run your figures through the FOV calculator or the lens selector.

Fixed dome vs varifocal vs motorised PTZ dome

Dome cameras split into three optical families, each with a different FOV control model and a different price point.

Fixed-lens domes (€60-180). The focal length is bonded into the lens assembly at the factory. Typical fixed lengths are 2.8 mm and 4 mm. Pros: lowest cost, smallest housing, lowest power draw (3-5 W), best optical sharpness for the price. Cons: no on-site adjustment — if the scene changes, you replace the camera. Use fixed domes for repeatable rollouts where one scene equals one SKU: hotel corridors, classroom blocks, retail aisles of equal width.

Motorised varifocal domes (€150-450). The lens has a motor-driven zoom and focus, typically 2.8-12 mm. The installer or operator sets focal length remotely via the camera web UI. Pros: one SKU covers every scene from 25 m² rooms to 80 m corridors, zero ladder revisits to re-aim, supports auto-focus on motion. Cons: 30-50% higher cost, slightly larger housing, mechanical zoom mechanism can fail after 5-7 years. This is the default choice for serious installs and the only sensible choice when scenes are not yet finalised at the design stage.

PTZ domes (€800-3000+). Pan-tilt-zoom domes combine a varifocal lens (typically 4.8-120 mm or wider zoom ratios) with motorised pan (360° continuous) and tilt (90-180°). The dome bubble is larger (140-260 mm diameter) to clear the rotating optical block. Pros: one camera covers what would otherwise take 6-12 fixed cameras, presets and tours allow scheduled coverage of multiple zones, optical zoom delivers identification-grade detail at 50-200 m. Cons: only one zone is covered at any instant — PTZ is not a replacement for fixed coverage of the same area, only an addition to it. See the full dome vs bullet vs PTZ comparison.

Sensor sizes (1/2.8", 1/2.5", 1/1.8") and FOV impact

Sensor size is the second variable that determines field of view at a given focal length. The naming convention (1/3", 1/2.8", 1/2.7", 1/2.5", 1/2", 1/1.8") is a legacy carry-over from vidicon tubes and does not equal the physical sensor diagonal in inches. Actual diagonal dimensions:

Larger sensor = wider FOV at the same focal length. A 2.8 mm lens on a 1/3" sensor gives ~96° HFOV; the same focal length on a 1/1.8" sensor gives ~126° HFOV. The larger sensor also has bigger photosites (typically 2.4 µm vs 1.4 µm), which collect more light per pixel and deliver 1-2 EV better low-light sensitivity. This is why a 4 MP 1/1.8" dome will outperform an 8 MP 1/2.8" dome in dim scenes despite the lower nominal resolution.

Specification sheets quote sensor size on the first line. If a dome is listed as "4 MP" with no sensor size, assume 1/3" — a budget unit. Premium 4 MP domes are always 1/1.8" or 1/2".

Resolution tiers: 2 MP, 4 MP, 5 MP, 8 MP — pixel density per metre

Pixel density per metre (PPM) is the only useful resolution metric for surveillance. It expresses how many horizontal pixels cover one metre of the scene at a given distance. EN 62676-4 sets thresholds: 25 PPM for detection, 62 PPM for observation, 125 PPM for recognition, 250 PPM for identification. The table below shows PPM at 5 m, 10 m and 20 m for a 2.8 mm dome at four resolution tiers, with a 108° HFOV (1/2.7" sensor).

Reading the table: a 4 MP 2.8 mm dome delivers recognition-grade detail (125+ PPM) only out to ~7.5 m. Beyond that, you have observation-grade footage, not face-identifiable. To extend identification distance, either raise resolution (move to 8 MP) or narrow the lens (switch to a 4 mm or 6 mm dome). For deep-dive on this tradeoff, read megapixels vs distance.

DORI distances for typical dome SKUs

DORI (Detection, Observation, Recognition, Identification) distances published by manufacturers follow EN 62676-4 pixel-density definitions. Below are official DORI numbers from three major manufacturers, each on a typical 4 MP dome SKU.

Use these as design anchors, not absolute promises — actual DORI depends on light level, contrast, motion blur and codec compression. For your own SKU and scene combination, the DORI calculator outputs the four distances given any lens-resolution pairing, and the DORI deep dive explains how the thresholds were derived.

IK10 vandal rating, IP66/IP67, operating temperature

Environmental ratings determine whether a dome survives where you mount it. There are three separate standards to read: IK (impact), IP (dust/water), and operating temperature.

IK ratings (IEC 62262) measure impact energy in joules. IK08 = 5 J (1.7 kg from 30 cm); IK10 = 20 J standard or 50 J reinforced (5 kg from 40 cm, equivalent to a strong baseball-bat strike). Specify IK10 for: schools, prisons, public transit, stadiums, ground-floor exteriors, and anywhere the camera is reachable by a person standing on the floor. Indoor offices and ceilings above 3.5 m can use IK08 or unrated indoor housings.

IP ratings (IEC 60529) are two digits: first for solids, second for liquids. IP66 = dust-tight + powerful water jets (12.5 mm nozzle, 100 kPa, 3 m distance, no harmful ingress). IP67 = dust-tight + temporary submersion to 1 m depth for 30 minutes. IP66 is sufficient for 95% of outdoor scenarios including driving rain and wash-down. IP67 is needed only where standing water or flooding is possible (basement entrances, dock walls, food processing). IP68 (continuous submersion) is rare and unnecessary outside of swimming-pool or marine applications.

Operating temperature. Standard domes operate -10°C to +50°C. Cold-environment domes ( -40°C to +60°C) include an internal heater that draws 4-8 W when active and requires PoE+ (30 W) or auxiliary 12 VDC. For installations in northern Europe, Canada or alpine regions, specify the -40°C variant — a standard dome's bubble can crack at -25°C and its LCD-shutter IR-cut filter fails to switch reliably below -15°C.

Combined outdoor spec. A safe baseline for outdoor domes in a public setting is: IP66 + IK10 + -30°C to +60°C + PoE 802.3af (or PoE+ if heater equipped). Verify all three on the data sheet; vendors sometimes meet two of three and quietly omit the third.

Mounting heights for ceiling vs wall vs pendant

Mounting height changes both the covered area and the pixel density at the target plane. Use these reference heights as starting points for design.

Indoor ceiling, flush-mounted dome. 2.4-3.0 m. Below 2.4 m the dome is vandal-exposed even indoors; above 3.0 m a 2.8 mm dome will exceed identification range at the perimeter of its FOV. For face capture at entrances, set the dome to 2.7 m and 0.5-1.5 m back from the door, angled 10° downward.

Indoor wall-mount, bracket-mounted dome. 3.0-4.0 m, with a 15-25° downward tilt. Wall-mounting is the right choice when ceiling installation is impractical (suspended ceilings with no plenum access, ducting in the way) or when you want a directional view rather than a 360° look-down. A wall-mounted dome at 3.5 m with a 4 mm lens and 20° tilt covers a 6 m wide × 12 m long zone at recognition-grade detail.

Outdoor wall-mount, eave or fascia. 3.5-4.5 m. Mount below the eave overhang to shelter the bubble from direct rain and sun, which reduces glare and extends bubble life. Tilt 20-30° downward for a typical driveway or yard view.

Outdoor pendant-mount, pole or beam. 4-8 m, with 6 m as the sweet spot for parking lots and forecourts. Above 8 m, a 2.8 mm dome at ground level falls below 125 PPM (recognition) even with a 4 MP sensor — switch to a 6 mm or 8 mm lens and accept the narrower FOV, or move up to an 8 MP sensor. For very tall pole mounts (10-12 m), pendant-mounted PTZ domes are more cost-effective than four or five fixed domes.

Tilt envelope. Every dome has a maximum tilt — typically 75-80° from horizontal. This creates a 10-15° blind cone directly below the unit. A dome at 3 m height has a 0.8-1.0 m diameter blind circle at the floor; at 6 m the blind circle grows to 1.6-2.0 m. Plan adjacent cameras to cross-cover these zones; see CCTV blind spots.

Common dome FOV mistakes

Five mistakes account for most underperforming dome installations. Each is fixable at design time and expensive to fix after install.

How to size a dome: worked example

Scenario: a retail floor 8 m wide × 12 m long, with a 3.0 m ceiling. The client wants recognition-grade footage of every visitor and is willing to accept observation-grade in the back corners. Budget allows one dome.

Step 1 — pick mounting position. Centre-mount the dome 4 m from the front door, 4 m from each side wall. The dome is at 3.0 m height, looking straight down with a 360° view at the bubble (we will use the dome's natural circular FOV).

Step 2 — calculate required FOV. The diagonal distance from the dome to the far corner of the room is √((8/2)² + (12-4)²) ≈ √(16 + 64) ≈ 8.9 m. To cover this with a downward-aimed dome at 3 m height, we need an HFOV wide enough that the projected radius at the floor is at least 8.9 m. HFOV ≈ 2 · arctan(8.9 / 3.0) ≈ 144° — too wide for a standard dome. Either re-position the dome (move to back wall and angle forward) or accept a 2.8 mm dome covering only the front 8-10 m at recognition-grade.

Step 3 — pick the lens. A 4 MP dome with a 2.8 mm lens on a 1/2.7" sensor delivers ~108° HFOV. At 3 m height, that covers a circle of radius 3 · tan(54°) ≈ 4.1 m at floor level — so a circle of 8.2 m diameter. The front 4 m × 8 m of the room is covered well; the back 4 m × 8 m sits just outside the recognition radius. PPM at 5 m ground distance is 186 (recognition+); at 8 m it is 116 (just below recognition).

Step 4 — verify against client requirements. The client wanted recognition for every visitor. The single-dome solution gives recognition only out to 7.5 m. To meet the brief, either add a second dome at the rear of the room (mirror placement, 4 m from back wall), or upgrade to a 4 MP varifocal dome at 4 mm focal length and move the dome to the rear wall facing the entrance — this gives a 84° HFOV and 200+ PPM all the way down the 12 m length.

Step 5 — replicate the math. Drop your floor-plan, dome position and lens choice into the FOV calculator to visualise coverage on a 2D plan; cross-check PPM at distance with the DORI calculator; pick the exact SKU using the camera catalog. For background on the underlying FOV math, see field of view explained, and look up any unfamiliar term in the glossary.