A modern camera or a digital camera uses an electronic sensor which has an array of light collecting photo-sites, each site representing one pixels (sensel). To understand how a digital sensor records an image let’s assume this sensor as an array of buckets which can be filled by a fluid called light. Each bucket has a way to tell how much light it contains to a memory card. Also, each bucket can tell only if it has more than a minimum amount of light and cannot contain if more light is fed into it than its size. So a bucket will not talk to the memory if there is light below the minimum specification. Also, the bucket will not be able to tell the memory if more light is fed into it beyond its capacity.
|A digital sensor under a microscope||An array of buckets with each bucket representing a pixel|
|Comparison of various sensor sizes. As the sensor size increases it becomes very expensive to manufacture but the advantage of better tonal gradations is demanded by quality professionals.|
Now, we often hear about the Mega Pixels (MP) of a camera. A 5 MP camera means that the sensor of that camera has 5 million pixels (photo-sites). It can be easily correlated that a lesser number of pixels arranged on a same size sensor will each be of a bigger size than more number of pixels arranged on a similar size sensor. This is primarily the reason why images from a 20MP mobile phone camera cannot compete with a 12MP DSLR in terms of image quality. So, at this point it is safe to assume that bigger the sensor the better will be the image quality. A bigger pixel size can respond to a wider range (minimum – maximum) of light intensity which means more contrast range and better colors.
Image information is recorded in a digital memory card. Information from the sensor is digitized by the camera processor (DIGIC by Canon, EXPEED by Nikon, BIONZ by Sony). Various camera companies advertise their processing technologies with their flagship cameras as this is an important step in creating stunning images.
Now after sensor light data is translated into current (i - ampere) data it needs to be stored in the digital memory. The bit depth of an image (8 bit, 16 bit or 24 bit) means how much tonal range can a pixel data store. 1 bit can only store one of two values, 0 (white) and 1 (black). An 8 bit image can store 256 (2^8) possible colors, while a 24 bit image can display about 16 million colors.
For simplicity you can understand it as, 2 bit image is like drawing with only 3 pencils on a white sheet. 8 bit image means drawing with 256 pencils of different shades.
It is clear now that each pixel on a photographic digital sensor is measuring light and storing that information on a memory card with the help of a processor chip. A camera must be able to control the light that falls on the sensor and make sure that it is neither too much nor too little. In film days the minimum light sensitivity of the film was limited by its chemistry but with digital sensors, the sensitivity of the pixels can be electronically manipulated. The sensitivity to light is represented by ISO (International Standard Organization) number.
This terminology is remnant of film days when each film type was rated for its light sensitivity based on its chemical composition. This was standardized so that each manufacturer releases similar rated films and Photographers can develop a better sense of other controls such as shutter speed and aperture.
It means that ISO 100 film by Kodak will be equally sensitive as Fuji Film ISO 100.
Electronic sensors offer this advantage over film sensors. It’s like being able to shoot with films of different ISOs, picture after picture.
This is the opening between the lens and the camera sensor.
|A representation of aperture opening denoted by f number. A lower number means wider opening.|
A bigger opening means that more light will get on to the sensor while a smaller opening means that lesser light will get onto the sensor. A bigger opening also results in shallow plane of focus or sometimes referred to as shallow depth of field (DOF).
|Large aperture opening results is narrow depth of field while smaller opening results in wider depth of field.||Depth of Field (DOF) refers to depth of things which are in focus or thickness of focal plane.|
Width of Plane of focus means the starting point sharp in focus and end point sharp in focus in the direction straight in front of the camera.
On the contrary, a smaller opening will have a very wide plane of focus referred to as wide depth of field (DOF).
Focus means the distance between lens and the subject. A subject at the right distance from the lens at a particular aperture will form a sharp image on the sensor. Modern cameras come equipped with powerful auto-focusing modes. Also, advanced camera bodies have a focusing motor while lenses with AF nomenclature have a focusing motor in them.
|Various Focus modes in Nikon or Canon.|
Most cameras have an Auto Focus S Mode for stationary objects for which distance between the subject and the camera is almost constant. Auto Focus C mode for continuous focusing is useful for fast moving subjects when distance between the camera and the subject is changing. Auto Focus auto mode is also there but same is not very useful as it results in missed shots.