# How a Mirrorless Camera Works

A guided cutaway of a full\-frame mirrorless camera: lens, aperture, sensor, live view, focus and shutter\.

By Yan Kurniawan

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/bHfWWdRriQmi)

## Guide

### 1. A camera without a mirror

A mirrorless camera makes a photo the way every camera does: a lens focuses light onto a sensor\. It leaves out the mirror and optical viewfinder of a DSLR, so the body is slimmer and the lens sits closer to the sensor\. Drag empty space to turn the camera, or click its shutter button\.

The model follows a full\-frame body of about 131 by 96 by 80 millimetres, the size of a Sony a7 IV\.

### 2. Light enters the lens

Light from the duck passes through several groups of glass\. Together they bend the rays so that each point of the duck meets again at one point on the sensor\. The image lands upside down and mirrored, and the processor simply reads it the other way round\.

Half of the body and lens is cut away here\. The lens groups are simplified\.

### 3. The aperture

Inside the lens, an iris of thin overlapping blades makes an opening of adjustable size\. A wide opening lets in more light, so the shutter can be faster\. A small opening lets in less light and keeps more of the scene sharp from front to back\. Move the slider to change the opening\.

The f\-number is the focal length divided by the width of the opening, so f/8 is a smaller opening than f/2\.

### 4. No mirror in the way

A DSLR puts a mirror at 45 degrees in front of the sensor to send the light up to its viewfinder, so its lens mount sits 44\.5 millimetres from the sensor\. Without the mirror box, this mount sits only 18 millimetres away\. The body gets shallower and the rear glass of a lens can sit close to the sensor\.

44\.5 millimetres is the flange distance of the Sony A\-mount used by its DSLR\-style cameras; Nikon Z mirrorless lenses mount 16 millimetres from the sensor\.

### 5. The sensor feeds the screens

With no mirror, the sensor sees the scene the whole time you frame it\. It reads out a fresh image many times a second, and the processor sends it to the electronic viewfinder and the rear screen\. The viewfinder is a tiny OLED screen behind a magnifying eyepiece, and it already shows the exposure and colour of the photo\.

The same live image is used to measure exposure and focus\.

### 6. Focus on the sensor

Some of the sensor pixels detect phase\. They compare light arriving through opposite sides of the lens, which tells the camera which way focus is off and by how much\. A motor then moves the focusing group straight to the right place\. Half\-press the shutter button to focus\.

Because focus is measured on the sensor itself, it can follow a subject almost anywhere in the frame\.

### 7. The shutter

A focal\-plane shutter in front of the sensor sets how long light falls on it\. It stays open while you frame the shot\. On a full press the front curtain closes and reopens to start the exposure, and the rear curtain closes to end it\. The sensor is read out, the photo is processed and saved to the card, and the shutter opens again\.

An electronic shutter skips the curtains and reads the sensor out directly, silently, at up to about 20 to 30 frames per second\.

### 8. Smaller, closer, faster

Here is the whole camera opened out: the lens and its mount, the shutter, the stabilised sensor, the processor board, the battery, the card and both screens\. Without a mirror box the body is smaller, the lens sits closer to the sensor, and one sensor handles framing, focus and the photo itself\.

In\-body stabilisation floats the sensor on a moving plate that counters hand shake\.