First, Let’s talk about each of them first.

CMOS (complementary metal oxide semiconductor) is a type of image sensor. In effect, it is the “eye” of a camera phone, digital camera, or video camera. It is a device similar to a computer chip, which senses light focused on its surface, like electronic film.

CMOS is one of two main types of image sensor. The other type is CCD.

In the past, CCD image sensors consistently provided better image quality. But now some (though not all) of the newer and better CMOS sensors match CCD quality.

CMOS sensors include basic image-processing circuitry that CCD sensors do not. This gives devices with CMOS sensors an edge when it comes to size, cost, and battery life.

CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) image sensors are two different technologies for capturing images digitally. Each has unique strengths and weaknesses giving advantages in different applications. Neither is categorically superior to the other, although vendors selling only one technology have usually claimed otherwise. In the last five years much has changed with both technologies, and many projections regarding the demise or ascendence of either have been proved false. The current situation and outlook for both technologies is vibrant, but a new framework exists for considering the relative strengths and opportunities of CCD and CMOS imagers.

Both types of imagers convert light into electric charge and process it into electronic signals. In a CCD sensor, every pixel’s charge is transferred through a very limited number of output nodes (often just one) to be converted to voltage, buffered, and sent off-chip as an analog signal. All of the pixel can be devoted to light capture, and the output’s uniformity (a key factor in image quality) is high. In a CMOS sensor, each pixel has its own charge-to-voltage conversion, and the sensor often also includes amplifiers, noise-correction, and digitization circuits, so that the chip outputs digital bits. These other functions increase the design complexity and reduce the area available for light capture. With each pixel doing its own conversion, uniformity is lower. But the chip can be built to require less off-chip circuitry for basic operation. For more details on device architecture and operation.

Since the very first digital camera, this one term has been shrouded in mystery. It has been the defining feature on digital cameras for years and has been built up and hyped to no end.

The megapixel race has boiled down to a catch phrase: “more is better”.

It makes sense why camera makers and retailers aren’t falling over themselves to clearly define megapixels to consumers: a megapixel number makes it easy to compare two different cameras.

“Our camera has 10 megapixels while our competitor’s only has 8. I’m sure you can tell which one is better.”

And - surprise, surprise - the more megapixels it has, the more a camera costs. Of course a salesperson is going to tell you that a camera with more megapixels is going to take better photos.

But what are these megapixels really good for? In the following paragraphs, you’ll find out.

Here’s some more math to help explain this: let’s say that you’ve taken a landscape photo with a 3 and 8 megapixel camera.

• The 3 megapixel photo is 2048 pixels wide and 1536 pixels high
• The 8 megapixel photo is 3504 pixels wide and 2336 pixels high

If you take these numbers and multiply them, that is where the megapixel number comes from:

• 2048 x 1536 = 3,145,728 (3 million pixels or 3 megapixels)
• 3504 x 2336 = 8,185,344 (8 million pixels or 8 megapixels)

Is More Better?

The answer is Not exactly!!

While a digital photo that contains 5 million pixels is larger than one with only 3 million, at small sizes they are hard to tell apart.

You should consider more factors than the Megapixel only, such as the correctness of color, the noise level, the distortion or perspective of the photo, or what we called the Quality of the picture!

This means the following for photos that contain a lot of pixels:

• It takes longer to transfer them from camera to computer
• You need more hard drive space to store them
• You need a more powerful computer to view and edit them

If more megapixels take up so much more space and there is no difference in image quality then what’s the point of mega-megapixel cameras?

The normal digital camera for daily or beginner should have at least 5 Mega pixels is enough.

Short for Single Lens Reflex, it a term associated with cameras and digital cameras. SLR cameras use a mirror between the lens and the film, or image sensor, to provide a focus screen. This means the image you see in the viewfinder (or LCD) will be the same as what appears on film or as your digital image.

Removable Lenses
No single lens can accommodate every photographic requirement, and SLR cameras have always used removable lenses. A wide variety of lenses are available for each camera system, and many lenses that fit 35mm analog SLRs also fit digital SLRs. However, the CCD or CMOS sensor in a digital SLR is generally not as large as a 35mm film frame, and there is typically a multiplier factor in focal length. For example, using a multiplier factor of 1.5x, a 50mm lens on a 35mm camera is equivalent to a 75mm lens when attached to a digital SLR.

Through the Lens
In an SLR, the photographer sees the image through the actual picture lens. To compose the picture, a mirror reflects the light from the lens to the viewfinder. When the picture is taken, the mirror momentarily flips out of the way to allow the light to pass through the lens diaphragm to the CCD or CMOS sensor (or to film in an analog SLR). Through-the-lens viewing enables precise manual focusing because tiny LCD screens do not have sufficient resolution. In addition, holding the camera against the face helps steady it.

With most digital SLRs, the LCD screen is used to review the recorded image, not to preview it for picture taking. In 2006, Olympus introduced the first DSLR with an LCD preview.

Beware the Dust!

Unlike an analog SLR, which uses a completely fresh film frame for each photo, the digital SLR uses the same sensor chip for every image. Unfortunately, that sensor is susceptible to dust, which is why DSLR users are advised to keep a lens on the camera at all times. In 2007, DSLRs began to include some form of built-in dust reduction or removal.

Cleaning the Sensor
DSLRs have a “mirror lockup” function that flips the mirror out of the way to expose the sensor for cleaning, and there is a raft of sensor cleaning materials on the market that cost from a few dollars to several hundred. For a comprehensive overview of all cleaning methods.