Digital Camera Sensors

In a digital camera, it is the sensor that acts as the photographic film, in that it is where the image is focused and captured.  The image is then either stored directly on the camera’s media (memory card), in the case of a RAW image, or processed to the settings within the camera, compressed, then stored on the media, in the case of a JPEG image.  Therefore the sensor is a very important part of the camera, and the capture process.

There are two types of sensor:

• CCD (Charged Coupling Device)
• CMOS (Compound Metal Oxide Silicon)

With the CCD sensors the charge builds up, once an image has been recorded, has to be read in a serial way, sensor by sensor, row by row.

CMOS sensors, on the other hand, have transistors for each individual sensor so that data from each of them can be read independently of the others.

Digital SLR Sensors

Within a modern digital SLR there is a sensor, but not necessary the same size as a traditional 35mm negative.

There are four sizes of sensor:

• APS-C
• APS-H
• Full frame
• Micro 4/3

Below is a diagram showing the difference between the APS-C and full frame sizes of sensor, which are the two most common sizes:

The APS-C and APS-H sized sensors get their names from the APS (Advanced Photo System) negative sizes (hence the last posting).  Where as the Full Frame gets it’s name from the fact that the sensor is the same size as a traditional 35mm negative.

The Micro 4/3 size is a newer size sensor as used in some of the newer Panasonic cameras and some of the micro system cameras.

One advantage that APS-C sized sensors have over full frame sensors is what is called a crop factor, where because of the smaller size of the sensor (in comparison to a traditional 35mm negative) a 200mm lens would seem to give the same focal length of a 300mm lens.  This is handy when taking photographs of subjects that are some distance away.

A comparison between a view from the point of a full frame and APS-C sensor is shown below:

So as you can see care has to be taken when using a camera fitted with a APS-C sized sensor when you wish to capture more of a scene or landscape.

There is a debate over which is better, APS-C or full frame, and below I will give some advantages and disadvantages, but I have to ask why did Canon use a APS-H in their flagship EOS 1D DSLR ?

Below are some points to consider when deciding:

Point	APS-C	Full Frame
Price	Cheaper	More Expensive
Image Quality	Good	Best
Viewfinder	Smaller	Larger and brighter
Lens availability	Wide choice of lenses	Limited choice of lenses
Crop Factor	Increases focal length	No crop factor

Personally, I think that technology is improving all the time, just look at the rave reviews of the Canon EOS 7D, which has an APS-C sensor, for example.

At the end of the day, if you are happy with what camera you have got, that’s what matters, after all it is not just down to the camera to capture the photograph, its the person behind the camera.

You can chase the technology and buy the latest, but there will be another one out soon after you have paid for it !