As we have already found out, image quality depends on sensor size. The large sensor allows larger pixels as well, and they are capable of catching more light, which results in clearer and less noisy photos with color rendition.

But it is necessary to remember that sensor size doesn’t mean resolution and its measure units are not megapixels but inches or millimeters.

The majority of modern digital cameras have basically little, 1/3.2″ or 1/2.5″ sensors; some advanced compacts may possess larger, 1/1.8″ ones. At the same time, the number of megapixels increases from year to year although 6 megapixels or so would be enough to view photos on a computer screen or make average-size prints.

But only large sensor can justify the usage of so many megapixels. Bigger resolution, no doubt, means better detail and the possibility to print large photos but if sensor remains the same and the number of megapixels increases, the size of every single pixel suffers – they become smaller. On big resolution but little sensors pixels are so tiny that they can’t capture enough light and you receive noisy pictures.

Unfortunately, that is the way digital cameras’ manufacturers go: nowadays 12-megapixel compact cameras are quite standard, though sensors are as tiny as they used to be. Although compacts are equipped now with different noise reduction technologies, they can’t fully compensate for it as the increase in the quantity of pixels on the same sensor will lead actually to the decrease in image quality.

Average users night be confused by the numbers they give for sensor sizes: 1/3.2, 1/2.5 inches. What should be remembered here is that bigger numbers in the denominator mean smaller sensors. The table below shows the correspondence of those ambiguous inches to a sensor’s physical size.

The biggest but one value for sensor size is 36 x 24 mm that is a frame size in 35-millimetre film. Such sensors have full frame DSLR cameras. APS-C DSLRs use 22.7 x 15.1 mm (1.6 crop factor) or 23.7 x 15.6 mm (1.5 crop factor) sensors.

The price tag of a camera largely depends on the sensor that it houses. That’s why compacts are affordable and aim at the middle-of-the-road audience, and full frames are expensive camera for professionals.

There are a lot of digital cameras nowadays: amateur and professional, compact and single lens-reflex, affordable and budget-breaking… But it is sensor type I would like to dwell on today.

Sensor is the most important unit in a digital camera. It is the place where the image is formed and later on stored. In film camera such function is fulfilled by film.

Most commonly and widely used sensors are CCD (charge-coupled device) and CMOS, though some companies use peculiar sensors of their own.

Sensor is composed of a great number of light-sensitive cells named pixels that transform light into electric signals. They are covered with filters – either red or green or blue (so called RGB scheme). Light beams of different spectrum have different wavelength, that’s why each filter lets through only certain types of beams. So in reality the picture is composed only of red, green and blue pixels – RAW files are written in such a way. For JPEG and TIFF files the processor calculates the colors to achieve the final image.

CCD and CMOS sensors differ in the way their data is read. In CCD sensors the value is read sequentially, that’s why file processing can take a lot of time. Such sensors are “thoughtful,” have bigger pixels and consume more power, and that’s why they are more expensive. But at the same time their strong points are as follows: they produce high-quality, low-noise images.

In CMOS sensors the information of each sell is read separately and it helps to achieve less data losses. With the creation of CMOS sensor Canon have made a breakthrough in technology. Now noise can be suppressed directly on the sensor, which leads to noise-freer images, and it is also possible to use such sensor for exposure metering and autofocusing. At the same time CMOS sensors are quicker.

CMOS sensor also offer better color rendition, though this parameter depends no so much on sensor type, but on sensor size. Where they definitely outperform CCD sensors is highlights. The latter suffer from blooming around very bright areas, while the former do not.

Of course, as the beginning of CMOS sensor production started later than that of CCD ones, at first they were more susceptible to noise, but now the development of both technologies lead to the situation when most drawbacks of them are overcome and the difference remains mainly in price and working speed.

In the era of film photography ISO (decoded as International Organization Standardization) was an indication of how sensitive a film is to light. Now this parameter is applied to digital cameras and defines the sensor’s light sensitivity. It is variable, i.e. you can specify it and record photos shot with different ISO levels on one and the same data medium. With film cameras you had to change the film to raise or lower ISO level.

The higher ISO level is, the more sensitive the sensor is and accordingly you can take handheld photos in low-light conditions without using flash. Higher ISO allows you to set faster shutter speed and consecutively to get crisper photos. And at the same time – noisier photos.

Noise in digital photography corresponds to grain in film photography. This undesirable effect shows itself in the way of colored dots that appear in a photograph.

Noise depends not only on ISO level but also on sensor size and on pixel size: the bigger the sensor is, the bigger are the pixels. The bigger pixels are, the more light they capture, and so the camera is.

Nowadays there are lots of consumer cameras with really tiny 1/2.3” sensors in the market. And though there’s a tendency to make compacts with larger sensors, their advantages are lost in megapixel race. Remember that of the two cameras with equal sensor sizes more noise will be generated by that one with more megapixels of resolution!

It is not as dramatic with digital SLR cameras as they have large sensors, not mentioning full-frame dSLR-s with 35mm sensors. That’s why they can generally take high-quality photos even at ISO 1600, 3200, or even higher speeds, while compact cameras tend to produce noisy images already at ISO 400.

Compact cameras also can take good-quality photos in good light, providing that you select the lowest ISO level. Moreover, small amounts of noise can be removed with the help of special software such as Noise Ninja, Neat Image and other without considerable loss in picture quality.