Walk into an electronics store to buy a camera, and the first model you will be shown to, invariably, is one with “a lot of megapixels”. The Megapixel rating of a camera is an indication of high many individual pixels of light it can capture, but it says nothing at all about the quality of these pixels. So pervasive is this selling strategy that many believe the MP rating to be the primary trait of a camera. Our phones now have sensors that handle 16MP, but does it seem reasonable to believe that all pixels were created equal when most top of the line kits operate at around 24?
Quality versus quantity is the maxim at hand, but what lay underneath the pixel that distinguishes one from the other? There are many specifications attributed to a camera that affect what kind of image it can produce. To give a brief list: ISO (light sensitivity), Aperture (how much light the lens commutes to the sensor), Shutter Speed, and CPU speed (which will affect the quality of autofocus systems and distortion correction). All of these considerations affect how much a pixel is actually worth, and depending on how well built the camera is, pictures will exhibit different amounts of distortion, noise, sharpness, brightness, and so on. Even cameras with similar qualities will differ, and the most important defense against being lost in the information, is to simply read reviews and look at the picture galleries they contain.
There are of course additional traits to a camera that make it a camera. To those that consider an on-board flash a mainstay, it may come as a surprise that an integrated flash horrifies professionals. The reason is that head-on lighting is one of the worst insults you can pay a subject, and softer, more natural brightness and contrast is achieved with a directional flash that can bounce light off of other surfaces. Above all, the lens that a camera has determines its window to the world; no sensor would be able to do without one. Professionals carry around many different lenses that fill a niche depending on where and what they want to shoot.
There all of course a myriad of differences and debates between the worlds of casual and professional photography. Whether your budget is $300 or $3000, better understanding what you’re buying is invaluable, and without fail, one of the best ways to insure this for yourself is to be educated. You will know you have reached this point when you are able to tell the salesman more about what camera he presents than he can.