Two settings, one result
When you buy a camera you choose two things that decide how useful the image will be: resolution and lens. Resolution is the number of pixels in the picture. The lens decides how much of the scene those pixels are spread across.
Together they set the key figure: how many pixels land on the thing you care about, such as a face or a number plate. Understanding that makes the spec sheet much easier to read.
What 2MP, 4MP and 8MP mean
"MP" stands for megapixels, meaning millions of pixels in each frame.
- 2MP is roughly the same as 1080p, a picture about 1920 by 1080 pixels.
- 4MP has about twice the pixels of 2MP.
- 8MP, often called 4K, has about four times the pixels of 2MP.
In practice, each step up lets you either cover a wider area at the same detail, or see more detail in the same area. It also creates a bigger video stream, which affects storage and network load. See how much storage CCTV needs and the bandwidth tool.
Typical uses, in general terms:
- 2MP is often adequate for close, narrow views such as a front door or a till.
- 4MP suits most general residential and small-business needs.
- 8MP suits wide areas, such as a yard or car park, where you may want to zoom into recorded footage.
None of these are rules. A well-placed 2MP camera can outperform a poorly placed 8MP one.
Pixels per metre: the number that matters
The useful way to compare cameras is pixels per metre (often written px/m): how many pixels cover one metre of the scene at the subject's distance. More pixels per metre means more detail.
The bands below are commonly quoted rules of thumb, not guarantees. Real results depend on lighting, lens quality, focus, motion and compression.
| Purpose | Rough pixels per metre | What it is meant to show |
|---|---|---|
| Detect | about 25 | Something is present |
| Observe | about 60 | General actions and clothing |
| Recognise | about 125 | A person you already know |
| Identify | about 250 | Enough detail to describe a person or read a plate |
These bands link back to the four purposes described in how many security cameras you need. A door camera might aim for the identify band, while a camera looking over a yard might be content with detect.
A worked example
Suppose a camera has a picture 2560 pixels wide (a typical 4MP width) and you want identify-level detail, about 250 px/m.
Dividing 2560 by 250 gives about 10 metres. That is the widest scene the camera can show while still meeting that target. So a front-door camera whose lens covers a scene about four metres wide would be comfortably in range, while the same camera covering a 20-metre driveway would sit well below it, closer to the observe band.
Now take an 8MP camera, about 3840 pixels wide. At 250 px/m, it can cover roughly 15 metres wide. At the 125 px/m recognise band, about 30 metres. This is why higher resolution helps on wide scenes: it moves a wide view from "detect" towards "recognise".
The field-of-view tool does this arithmetic for you using your distance and lens.
Focal length and field of view
The lens focal length, in millimetres, controls how wide or narrow the view is.
- Short focal length (for example 2.8 mm) gives a wide view. Good for rooms, small yards and covering a lot of ground at short range.
- Medium (for example 4 mm) gives a balanced view, common for doors and driveways.
- Long (for example 6 mm and above) gives a narrower, more zoomed view. Good for distant subjects, such as a gate at the far end of a long driveway.
- Varifocal lenses let an installer adjust the view on site rather than being fixed. They suit sites where the exact distance is hard to know in advance.
Wide lenses also tend to show some edge distortion, and subjects at the edges appear smaller and softer. A lens that is too wide can make a camera look as if it covers everything while recording nothing identifiable.
The trade-off is simple. A wide lens covers more but gives fewer pixels per metre. A narrow lens covers less but gives more.
Choosing sensibly
- Decide the purpose first, whether detect, observe, recognise or identify.
- Estimate the distance to the subject and the width of the scene.
- Pick the lens that frames that scene without wasting space.
- Pick the resolution that gives the pixels per metre you need.
- Check that the recorder supports the chosen resolution and number of cameras. See NVR explained.
Things resolution does not fix
- Poor light. A high-resolution camera in a dark corner is still a poor camera. See night vision.
- Bad angle. Mounted too high or aimed away from faces, extra pixels will not help.
- Motion blur. Fast movement can blur at slower shutter speeds, which are common at night.
- Compression. Heavy compression to save space removes detail. See H.265 vs H.264.
Honest limits
The bands above are guides, not promises. A clear identification still depends on the day, the light and the person's movement. Smart detection features, available on compatible systems and varying by camera and recorder, can flag a person but do not add detail that the sensor did not capture.
If you are unsure what to pick for a given spot, ask us about installation and describe the distance and the purpose.
Frequently asked questions
Is 8MP always better than 4MP?
No. It gives more detail on wide scenes, but it also needs more storage and network capacity. For a close door view, 4MP is often plenty.
What is the difference between 4K and 8MP?
For security cameras they usually refer to the same thing, a picture around 3840 by 2160 pixels.
Will a wider lens give me a better view?
It will cover more, but with fewer pixels per metre. Often two cameras with narrower lenses give better evidence than one very wide camera.
Can I zoom in later on recorded footage?
You can enlarge the image, but you cannot recover detail that was never captured. Digital zoom on a low pixels-per-metre scene just enlarges blur.
What is a varifocal lens?
It is a lens with an adjustable focal length, so the installer can tune the field of view on site. It is useful when the exact distance is uncertain.