First, the things every photographer thinks about, and that every camera may or may not let you control.
Exposure, aperture, and sensitivity are the three fundamentals of photography. Exposure is how long the shutter is open; aperture is how wide the shutter is open; sensitivity is how sensitive the film (if you’re using film) or the digital sensor (if you’re using a digital camera) is to light. That’s it.
A fast exposure is used to freeze movement or reduce blur. A slow exposure is used to let in more light, and get a better picture when light isn’t good. However, a long exposure will also increase blur, whether from the subject moving, or the camera. A small aperture lets in less light but gives greater depth of field –this is basically how much of the image is in focus. For instance, if a person’s face is in sharp focus but the background is blurred (often a desirable effect in portrait photography) the depth of field is shallow, if something in the foreground and something in the far background are both in focus then you have a greater depth of field (which you might prefer for documentary or landscape photography.)
Sensitivity is fixed with film and is expressed by the ASA number; ASA 100 film is not very sensitive while ASA 3200 film can be used for nighttime photography. In digital photography sensitivity is expressed by the ISO number, and here’s a critical difference between film and digital –with a digital camera you can vary sensitivity of the sensor (with film, you’d have to change film.) Most modern digital cameras can go anywhere from 1-200 ISO all the way up to five or even six digits, though the high end of any camera’s ISO range is usually solidly in not-great-but-better-than-nothing territory.
Second, digital cameras record images with a sensor.
The sensor of a digital camera is basically a chip with light sensitive photo sites on it –what it does is very simple; it turns light into a digital file. This is what’s stored on your camera’s memory card, and when you look at a picture on your computer, the computer’s basically reading the file and turning it back into a picture again. If you look at cameras at all you’ll probably have noticed that the amount of information the sensor can capture is measured in megapixels, or millions of pixels. The most important thing to remember is that more is not necessarily better —the ultimate effect a given pixel count has on image quality depends on a host of other factors, including the quality of your lens (or lenses), presence or absence of image stabilization, software used by the camera to process information from the sensor, and so on. Your mileage may vary but unless you’re in the habit of heavily cropping or printing poster size, 12-16MP is more than you’ll ever really need (and in the former case, c’mon, you can frame better than that.)
Sensor size, however, is extremely important. All other things being equal, you’ll probably want the biggest sensor you can afford and are willing to carry around. A bigger sensor means better low light performance, and probably less noise (the equivalent of static in the sensor, which shows up as graininess and distorted color) as well. A bigger sensor also gives you more control over depth of field –if you’re looking at a good camera because you’re interested in getting portraits with the creamy-dreamy blurred background you’ve noticed in pro portraits, you’ll need a bigger sensor (and the right lens, of course.)
The biggest commonly used sensors are so-called full frame sensors, which reproduce the area of a 35mm film negative –superb image quality, but full frame cameras are usually anything from very expensive, to very, very, very, what-the-hell-that-was-the-kid’s-tuition expensive. A good compromise is to go one step down, to so-called APS-C sensors which are used in many enthusiast, or so-called “prosumer” cameras, or to Micro Four Thirds, which is yet smaller, but still big enough for excellent results in most cases, especially when paired with the right lenses.
Now, if image quality were the only consideration, we’d all be lugging around $3-7000 camera bodies that weigh as much as a Smart Car, with lenses that look more as if they were made by Krupp’s of Essen instead of Nikon. We’d all be producing sharp, technically impeccable pictures most of the time, with accurate color, under all sorts of lighting conditions. We’d also all be broke, and unable to pay our chiropracter bills from hauling around thirty pounds of camera gear every time we want to take some happy snaps of the kids at a picnic. This brings us to Part The Third:
What kind of photographer are you?
For most casual photographers a cell phone camera is all they’ll ever need. For many, though, a cell phone cam is ultimately too limiting. Cell phone cameras handle low light very poorly –even today, when they’re better than they’ve ever been –and they focus very slowly, especially in anything other than optimum lighting conditions. While good photographers can get excellent results with cell phone cameras, they still don’t do very well outside anything other than really good light, with a slow moving or immobile subject, as the plethora of Facebook pictures of unrecognizable people doing who knows what who knows where can testify. Here’s a necessarily incomplete list of what’s on the street for someone looking to trade up from a cell phone camera.
Full article read on