If you've been into photography for a while, you know the difference between single lens reflex (SLR) cameras and small pocket-style cameras. SLRs offer a lot more flexibility. They generally use better lenses, and you can attach a variety of lens types from wide-angle to telephoto to zoom. They allow full manual control of exposure and focus. When composing your photo, you're looking right through the lens. These and other features of SLRs allow you to be a more creative photographer, and you might get better pictures.
Digital SLRs offer the features mentioned above, plus a very important advantage over smaller cameras; larger sensor size. The image sensor in a digital camera is what captures the photograph, much like film. The quality of the image sensor has a pronounced effect on the quality of your pictures.
Most pocket-size and mid-size cameras use an image sensor about the size of a pencil eraser; typically in the 25 to 38 square millimeter range. That's a very small device on which to jam several million light sensing pixels. Digital SLRs, on the other hand, use sensors that are from 225 to 860 square millimeters. That's 10 to 30 times larger. While bigger sensors are more expensive to manufacture, they generally produce higher quality images. It's easier to get millions of the light sensing pixels onto a larger surface.
Both CCD and CMOS image sensors capture light using a grid of small photosites on their surfaces. It's how they process the image and how they are manufactured that differ one from another. Despite the differences, both types of sensors are capable of providing very good results and both types are used by major camera companies.
As digital cameras have improved over the years, buyers have learned that more megapixels (millions of pixels) means better, high resolution pictures. That's true to a point, but the problem is there's a practical limit to the number of high-quality pixels a tiny sensor will hold. The marketing people at the camera companies keep pushing for more megapixels because they know they can sell more cameras. The result is that photos taken with some newer small cameras are getting worse, not better. The megapixel technology threshold is being exceeded... due to marketing demands. We believe the reasonable limit for a small image sensor is about six megapixels. Beyond that, your images suffer from lack of detail, noise, and artifacts produced when sharpening and noise reduction techniques are employed to attempt a fix.
However, with dSLR, there is a discernable improvement in moving from six to 10 megapixels because of the larger sensor sizes. The entry level digital SLR market, generally defined as dSLR cameras that sell for US$1000 or less, has certainly expanded at both the bottom and the top. Today you can actually buy a digital SLR camera in the US$400 to US$500 price range. To choose the digital SLR camera that is right for you, consider this handy four step guide.
So, if you seek the best image quality, or plan to print your photos at very large sizes, consider a digital SLR. At the very least, consider the sensor size in the cameras you look at. Don't choose one based simply on its pixel count. We've achieved much better photos with a 5-megapixel 38mm image sensor than with an 8-megapixel 25mm image sensor. In this case, size really does matter.