Question 1

How does camera autofocus actually work?

Accepted Answer

By one of two fundamentally different strategies — **measuring how out of focus the image is**, or **hunting until it looks sharpest** — and the difference explains why some cameras snap to focus instantly and others visibly wobble.

**Contrast detection.** The camera moves the lens and measures **edge contrast** in the image, on the assumption that a sharper image has higher contrast. It must move past the point of best focus to know it has found it, then come back. Accurate, requires no extra hardware, and inherently slower with a characteristic **hunting** motion. It also cannot tell which direction to move initially.

**Phase detection.** Light from opposite sides of the lens is compared. If the image is in focus, the two views align; if not, the **direction and size of the mismatch** directly indicate how far and which way to move the lens. **One measurement, one movement** — which is why it is dramatically faster. Originally this needed a dedicated sensor and mirror in a DSLR; modern cameras and phones use **on-sensor phase detection**, with specially arranged pixels across the sensor, and **dual-pixel** designs where every pixel is split into two halves that each see a different side of the lens.

**Hybrid systems** are the norm: phase detection to get close quickly, contrast detection to confirm precisely.

**What else phones use:** a **laser or time-of-flight sensor** measuring distance directly, useful in low light and at short range; and increasingly **subject recognition**, where a neural network identifies faces, eyes, animals or vehicles and tells the focus system what to track — which has changed the practical experience more than any optical advance.

**Why it fails:** low light and low contrast; flat featureless subjects; shooting through glass or fences, where the camera chooses the wrong plane; backlighting; and repetitive patterns confusing phase detection.

**Practical points:** aim at an edge rather than a flat area; use single autofocus for still subjects and continuous for moving ones; and remember that a wide aperture gives shallow depth of field, so **accuracy matters more the faster the lens**.

Question 2

What is the difference between optical and digital zoom?

Accepted Answer

Optical zoom moves glass. Digital zoom crops the image. Only the first adds detail. Optical zoom physically changes the lens's focal length, or switches to a different lens with a longer one. Light

Question 3

What is the difference between optical and electronic image stabilisation?

Accepted Answer

OIS moves hardware to counteract shake; EIS crops and adjusts the image in software. They address the same problem differently, and increasingly appear together. Optical image stabilisation (OIS).

Question 4

What is computational photography?

Accepted Answer

Using processing rather than optics to produce an image — capturing multiple frames and combining them computationally, which is how a phone with a tiny lens produces photographs a small sensor

Question 5

Why does my TV picture look like a soap opera?

Accepted Answer

The effect comes from motion interpolation, a feature enabled by default on most televisions and given a different marketing name by every manufacturer. The television generates artificial frames

Question 6

How does a camera sensor capture colour?

Accepted Answer

It does not, directly — sensor pixels only measure brightness. Colour is produced by placing tiny coloured filters over them and then reconstructing the missing information computationally. The Bayer

Question 7

How does a fingerprint sensor work?

Accepted Answer

By building an image of the ridges and valleys of your fingertip, then comparing extracted features rather than the picture — and the three sensing technologies have meaningfully different strengths.

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