Digital SLR cameras closely resemble their film camera predecessors.
Many older film cameras made it difficult to compose a photo effectively because the image in the viewfinder didn't correspond to the image seen through the main lens. This difficulty was resolved by single lens reflex (SLR) cameras, which used a mirror to show the photographer exactly the same image that would be exposed on film. Digital SLRs work the same way, except that the image is received on an electronic CCD sensor rather than photographic film. These digital SLRs, or DSLRs, are available in inexpensive starter models and high-end professional models, but the differences aren't always obvious.
CCD Sensor
The heart of a digital camera is the charge-coupled device (CCD) sensor, which works like your computer screen in reverse. It's an electronic device that detects light and turns it into an electronic signal. The image is measured in thousands of pixels, or megapixels, but even entry-level cameras have high pixel counts. Top quality DSLRs have a CCD sensor the same size as a 35-mm film, meaning it can be used with the same lenses as a film SLR. The sensor in entry-level models is roughly one-quarter the size, yielding images without the depth of field that's available from a top camera.
Exposure and Focus Control
A second major difference between entry-level and professional DSLRs is their handling of exposure and focus controls. Entry-level DSLR cameras are mass-market devices, aimed at users who have limited knowledge of photography but want a few more features than point-and-shoot cameras can provide. Their design includes a number of automatic settings, allowing inexperienced users to create acceptable photographs in a wide range of conditions. Professional models have relatively few presets, since manual control of focus and exposure is part of the photographer's art.
Lenses
The smaller-sized CCD sensor in entry-level DSLR cameras has an impact on lens selection. Lenses for film SLRs can be used on a professional DSLR with a full-frame CCD because it's the same size as a frame of film. Entry-level DSLRs need special lenses that scale down the image for the smaller sensor. These are often less costly than professional-quality lenses, which can rival the camera itself in price. In skilled hands, both types of camera and lens can produce excellent images, but professional lenses take full advantage of the better cameras' depth of field.
Depth of Field
There's little visible difference between high- and low-end digital SLRs except that professional models are physically larger to accommodate the large CCD sensor. However, the differences in image quality can be substantial. The small CCD in an entry-level DSLR produces relatively "flat" images, similar to those from a point-and-shoot camera. Professional cameras, on the other hand, can create images with a feeling of depth and space, which is referred to as depth of field. It's the cumulative result of the camera's larger sensor and better lenses and the photographer's skill in manipulating the manual exposure and focus controls.
Tags: depth field, difference between, DSLR cameras, entry-level DSLR, except that, exposure focus controls, focus controls
