Wednesday, 22 September 2010

Unit 205 D1 Photo Imaging Equipment - Sensors


What it all about this sensor size? Does size really matter?

Well here it is..... this is basically it... The bigger the sensor the more light it gathers, more light equates to more information, more information means better quality of final image, the size of a camera sensor will have a big impact on the quality of your pictures. Larger sensors also preform better in low light situations as they produce less noise than smaller sensors.

Pixel density
One thing to keep in mind is that the size of each individual pixel is what will define the performances of the sensor. In other words, more pixels over the same area means that noise levels will increase, because each individual pixel will receive less light.

Compact Digital Camera Sensors
Most compact camera sensors are equivilent in size and they are measured diagonally, the most common sizes are 1/2.5 and 1/2.3 inches which by any standard is pretty small

Larger Compact Camera Sensors and Bridge Cameras
Manufacturers have started including larger sensors in some of their compacts. For instance, Canon's S90 has a 1/1.7 (0.58) inches sensor. This represents a total area 37% larger than most comparable models, and yields much better low light pictures. Compact cameras like the Panasonic LX5 also sport larger sensors.

DSLR Sensors
The sensor in a typical digital single lens reflex camera is many, many times larger than the sensors found in compacts. This means that DSLRs are much better at taking low-light pictures with low noise. But even in the DSLR world, there are differences between sensors.

The larger sensors are called “full-frame” and are found in some higher-end, professional bodies. The size of these sensors is equal to that of 35 mm film, with a 1.7 inches long diagonal.
The vast majority of DSLRs have sensors slightly smaller called APS, with a 1.18 inches diagonal (48% of the area of the full frame sensor). The use of the APS sensor allows smaller lenses to be designed while still preserving most of the optical performances of the sensor.
Another sensor size used in DSLRs is called Four Thirds (0.85 inches diagonal). This system, while being slightly less efficient in low light, makes possible the use of extremely small lenses. This sensor size is also used in the “micro Four Thirds” system, which is a bridge between compacts and DSLRs.

Medium Format Sensors
These cameras are still mostly of the film variety with sizes as decribed in my last entry on camera formats.If you are using a camera body with a maximum format capability of 6x7cm, then you will normally be able to use backs with film sizes 35mm, 35mm panoramic, 6x4.5cm, 6x6cm, up to 6x7cm. Digital wise there is also an increasing range of digital backs available. These allow you to maximise your investment in Medium Format equipment by adding digital capabilities. The first Medium Format cameras built for digital photography are now becoming available.

Types of Sensors
CMOS has become the current mainstream of chip design. It is capable of incorporating a great many additional functions right on the chip, including analog to digital conversion (ADC) and other aspects of image processing. Combined with the fact that more capabilities can be built right on to the chip, and the fact that the fabrication plants are used for chips found in many other contemporary silicon products, CMOS designs are much less expensive to build. In combination with the higher circuit density allowed by integrating more functions on the chip, you end of with lower costs and smaller ultimate size, an important factor when used in small cameras, such as those in cell phone, for example. CMOS sensors also use less power than do CCDs.

CCDs, though eclipsed long ago for use as memory devices, and needing additional off-chip processing circuitry, are still in use at the high end of image capture, including in all medium format digital backs. The reason for this is their superior image quality. They have the potential for greater light sensitivity, lower noise and higher dynamic range. This is not to say that there aren't CMOS cameras that are capable of very good, even excellent performance in these areas. But, one has to ask why companies like Phase One, Leaf, Hasselblad / Imacon, and various military and scientific applications prefer to use CCD chips, in spite of their higher costs, greater power needs and other drawbacks. The answer likely comes down to one thing – image quality.

Next installment... flim Vs digital

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