Easy Basic Photography
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Digital Camera Image Sensors and Sensor Size
The image sensor in a digital camera is a device whose purpose is to capture and process information about the
light that enters the camera through the camera lens. There are millions of light collecting areas on a sensor that
are called "photosites". The light from a scene that is collected in these photosites are individual picture elements
that are better known as "pixels". One million of these pixels are equal to one megapixel.
Image sensors convert light to an electric charge which is then converted to a voltage value, which is converted
to digital information to be stored in the camera memory. The stored digital information is then reproduced as the
final image or "the picture". The total process is much more complicated than this but the point here is just to give
you a basic understanding of the function of a sensor.
Most consumer cameras use one of the two following types of sensors.
CCD Sensor (Charge Coupled Device): A CCD Sensor reads the amount and quality of light captured in each
photosite sequentially. (one at a time) That information is then transported to additional circuitry in a different
area of the sensor where it is converted to digital information..
CMOS Sensors (Complementary Metal Oxide Semi Conductor). Light measurements taken at the photosites
in CMOS sensors are processed simultaneously rather than sequentially. Most of the processing circuitry for
converting light to a charge is located at each sensor photosite so that the information doesn't have to be
transported to be converted to digital information. This makes for quicker loading and processing of the
information about the light.
CCD or CMOS-Which is better? Both of these sensor types perform the exact same function, but use different
techniques for capturing the images digitally. The differences in their performance are slight.
For instance, CCD sensors have a better dynamic range performance but CMOS sensors use less power.
CCD sensors produce images with less noise but CMOS sensors process information faster.
There are other differences, but none that give one sensor a distinct advantage over the other. In other words,
the type of sensor should not be a main factor in deciding which camera to buy.
Major camera companies like Canon and Nikon have begun to primarily use CMOS sensors for their Digital SLR
cameras while using CCD sensors for their Digital Compact cameras. Just take note that a part of the decisions
they make about which sensors to use might have a lot to do with production costs and which type sensors they
prefer to market. It's not only about one sensor being so much better than the other.
Although there are differences in the way these sensors operate, at this time, there is no significant difference in
the quality of the final images each type image sensor produces. (especially in the eyes of the average
photographer.)
Sensor Size and Pixel Size
Digital camera image sensors are made in various sizes. Most Digital Compact cameras like the Canon
Powershot A3300IS use a 1/2.3 size image sensor as seen in the diagram.
The APS-C sensor is the size most commonly used sensor size for consumer level Digital SLR cameras like the
Nikon D5000.
Mirrorless Interchangeable Lens Cameras like the Panasonic Lumix G2 use the Four Thirds system sensors.
These diagrams do not represent actual sensor sizes. They are for comparison of the sizes only. However, the written numeric
dimensions are actual sizes of each of the particular image sensors shown below.
35mm/Full Frame APS-C Four Thirds System 1/1.7 1/2.3
36 x 24 mm 23.6 x 15.7 mm 17.3 x13 mm 7.6 x 5.7 mm 5.76 x 4.29 mm
(note: Canon manufactures their own APS-C sensor size which measures 22.2 x 14.8 mm)
A full frame sensor is around the same size as the image area on 35mm film. Full frame sensors are usually
found in higher end and professional cameras. In discussions about sensor size, the comparisons are usually
made in reference to a smaller size sensor as compared to a full frame size sensor.
As you can see, Compact Camera sensors (eg: the 1/2.3 sensor size) are drastically smaller than the image
sensors found in Digital SLR cameras (like the APS-C sensor size).The Compact cameras sensors also tend to
have smaller size pixels than the Digital SLR camera sensors.
A Digital SLR camera with its larger sensor as well as larger pixel sizes, will produce higher quality images than a
Compact Digital camera with its smaller sensor and pixel sizes. That is, even if both cameras have the same
amount of pixels.
Larger size pixels are able to gather more light and information about the quality of the light and will produce
better images in terms of "noise" and "dynamic range".
Noise is dark or light specs in the image that are more apparent when pictures are taken in lower light settings
and/or as the ISO (camera light sensitivity) setting is increased. Cameras with larger sensors and pixels are able
to gather more light, and produce images with less noise in these situations.
Dynamic Range is the ability of the sensor to more evenly capture the highlight (bright) and shadow areas of an
image. A larger sensor will have a better dynamic range than a smaller one.
Generally, the smaller sensors found in compact cameras will produce images that are more than acceptable for
casual photographers.
However, the more serious photographers who pay more attention to details and want even higher quality in a
picture will be better off with a camera with a larger sensor.
CCD Type Image Sensor
