How does a digital camera work?
By Ashok Kandimalla
While millions of photographers use cameras and take zillions of pictures, very few know how a digital camera (or digicam for short) actually works. To understand how a digicam works, you need to first learn about the components of a digicam (see Pictures 1, 2 and 3). You can then see how they all work together to capture an image.
- Camera body – A light tight box that houses all the components.
- Sensor * – Captures the image (Picture 3). It consists of a number of light sensing dots called picture elements or pixels. All the pixels put together form the image. Normally pixels are in millions and the total number of pixels is called the pixel count. If there are 12 million pixels in your camera then pixel count is 12 mega pixels or 12MP.
- Shutter* – Allows light to fall on the sensor for a precise amount of time. The faster the shutter operates, the lesser the light it allows to fall on the sensor.
- Lens – The eye of the camera! It needs to be focused to get a sharp image. Note that a lens inverts the image but is corrected back in the camera (Picture 3).
- Diaphragm * – This is similar to the iris of eye and is inside the lens. It is made up with a set of blades that form a hole in the middle, called aperture. The size of the aperture regulates the amount the light going through the lens – smaller the hole, lesser the light that goes through and reaches the sensor.
- Exposure meter * – Measures the intensity of light and sets the exposure to record the image correctly -not too dark or too light.
- CPU * – The brain of the camera. It is responsible for setting the focus and exposure. It also processes the captured data into an image.
- Buffer – The data captured by the sensor is first temporarily stored in this and then processed by the CPU.
- Memory card – Stores the image that has been processed by the CPU. This can be removed from the camera and the images read out into a computer for viewing, sharing or printing. You can process them even further on your computer.
- Viewfinder – This is not present on all the cameras but is useful as it shows what you are going to photograph. (An LCD monitor can also be used to see what you are going to photograph, but unlike a viewfinder it is difficult to use if the ambient light is bright).
- LCD Monitor – This allows you to see what you are photographing (like a viewfinder) and review the picture you have taken. You can also check if your image is correctly exposed.
- Shutter release button (erroneously called “Click”) – You need to press this to take a photograph.
- Flash: Gives a bright pulse of light. You can use it as a light source when natural light is low.
- Zoom Control – This make what you see and record bigger or smaller. Here T means Tele (makes your subjects appear bigger) and W means wide-angle (makes your subject appear smaller and includes more of the scene). Sometimes, zoom control is like a ring on the lens.
- Mode dial – Helps you set various exposure modes
Items marked * are inside the camera (Picture 3) and hence you will not be able to see them from outside.
So how do all these work to get you a picture? To understand further, look at Picture 3 that shows the cross section of a camera.
As a photographer you would first decide on what to photograph. So you “frame” a scene with help of a viewfinder or the LCD monitor. Then, you press the shutter release to freeze that moment. Now, a lot of things happen!
1. The lens is focused to get a sharp image,
2. Exposure (shutter speed and aperture size) is set
3. Shutter opens
4. Image is captured on the sensor as pixels.
5. The shutter now closes.
6. The pixels are written into a buffer.
7. The data in the buffer, which is in the form of pixels, is then processed by the CPU to create an image.
8. The image is then written on the memory card.
9. You can retrieve the image from the card and use it for sharing, printing or further processing.
All text, diagrams and images © Ashok Kandimalla.