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What a 8 mm security camera lens covers at 10 feet

Published standard Lens geometry and nominal sensor optical format
Quick answer

A 8 mm lens on a 1/2.8 inch sensor has a horizontal field of view of 35.5 degrees, which covers a scene 6 feet wide (2 m) at a distance of 10 feet. That is about 2 average parking spaces, or the full width of a typical two car driveway only partly.

How this is worked out

scene width = 2 x distance x tan(horizontal field of view / 2), where field of view = 2 x atan(sensor width / (2 x focal length))

Sensor width is set by the optical format. The "1/2.8 inch" naming is a legacy convention from vidicon tubes rather than a real measurement, and the nominal width used here is 5.12 mm, which is the figure the industry uses for that format.

Coverage width of a 8 mm lens by distance
DistanceScene widthIn metresRoughly
5 ft 3.2 ft1 mA doorway
10 ft 6.4 ft2 mA single car
15 ft 9.6 ft2.9 mA single car
20 ft 12.8 ft3.9 mA two car drive
30 ft 19.2 ft5.9 mA two car drive
40 ft 25.6 ft7.8 mA small garden
50 ft 32 ft9.8 mA small garden
75 ft 48 ft14.6 mA small garden
100 ft 64 ft19.5 mA wide frontage
Coverage width grows linearly with distance, so a lens that covers 6 feet at 10 feet covers twice that at twice the distance, with half the pixel density on anything in it.
Pixel density at 10 feet, by sensor resolution
SensorHorizontal pixelsPixels per metreDORI level reachedGood enough to
2MP (1080p) 1920984IdentifyA stranger can be identified from the footage to an evidential standard.
4MP (1440p) 25601312IdentifyA stranger can be identified from the footage to an evidential standard.
5MP 25921329IdentifyA stranger can be identified from the footage to an evidential standard.
8MP (4K) 38401969IdentifyA stranger can be identified from the footage to an evidential standard.
12MP 45122313IdentifyA stranger can be identified from the footage to an evidential standard.
At 10 feet on a 8 mm lens, resolution is what separates a camera that identifies someone from one that merely records that somebody was there.

Choosing between coverage and detail

Every lens choice is the same trade. A 8 mm lens at 10 feet gives you 6 feet of width, and every extra foot of width costs pixel density on whatever is in the frame. There is no camera that avoids this, only sensors with more pixels to spread.

The practical approach on a real property is to stop trying to make one camera do both jobs. Use a wide lens for awareness across an open area, and put a second, longer lens on the one approach path where you genuinely need to identify a face. Two cameras doing one job each will outperform one camera compromising between them, and usually for less money.

Mounting distance is a design choice, not a constraint

The distance in this calculation is the distance from the camera to the subject, and it is often adjustable. Moving a camera closer to a gate rather than covering the gate from the house can transform what the footage is worth, and it is free.

The limit is usually cable, and the Ethernet channel limit of 100 metres is generous enough that camera placement is rarely constrained by it on a residential property.

Cameras with the reach for this distance

Optical zoom cameras first, because optical zoom is the only thing that adds pixels to a distant subject.

Common questions

What field of view does a 8 mm security camera lens have?

About 35.5 degrees horizontally on a 1/2.8 inch sensor, which is the most common format in residential cameras. The same lens on a larger sensor gives a wider field of view and on a smaller one a narrower field, so the focal length alone does not determine coverage without knowing the sensor format.

How wide an area does a 8 mm lens cover at 10 feet?

About 6 feet, or 2 metres. Coverage scales linearly with distance, so at double the distance the same lens covers about 13 feet, with correspondingly fewer pixels landing on any person within it.

Should I choose a wide angle or a narrow lens?

Wide for awareness, narrow for evidence. A wide lens covers a whole area so you can see what happened, and a narrow lens puts enough pixels on a face to prove who did it. Most properties need both, placed on different approaches, rather than a single compromise lens that does neither job well.

What is a varifocal lens and is it worth it?

A varifocal lens can be adjusted across a focal range rather than fixed at one length, so the coverage can be tuned after the camera is mounted. It is worth the extra cost where you cannot predict the right framing in advance, which is common on a first install, and it removes the risk of buying a fixed lens that turns out to be wrong.

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Keep going

Before you point a camera at anything. Aim cameras at your own property and your own boundary, never into a neighbour's windows or across their garden. Cameras in bedrooms, bathrooms, or anywhere else a person reasonably expects privacy are a serious legal problem, and that includes guests, lodgers and anyone who works in your home. Audio is legally different from video, many US states require the consent of every party to a recorded conversation, and several recorders capture audio by default, so check your own state before you enable it. Some places require visible notice that recording is taking place, and landlords and homeowner associations often impose their own rules on top. This is researched general information and not legal advice, and the law varies by state and by country.

And once it is installed. Change every default password, keep the firmware updated, and be clear with yourself about where the footage goes: a cloud camera means a third party holds recordings of your home, while a local recorder keeps them in your house. That is a genuine buying consideration, not a technicality.