How many mega pixels should a camera have if you want to be able to print at least a good quality 8x10 photo?

Pixels are tiny building blocks of color in an image; the more you pixels there are, the more detailed the image will be. A mega-pixel is a set of one million pixels; most DSLR cameras have a range of around 10 megapixels up to a mind-blowing 50 megapixels.

How many mega-pixels you have is not really the most important factor in getting good images, though. It sure is quite important in getting sharp images, but even more important is the lens, or "glass" that is used. For example, a camera with twelve megapixels paired with a very good quality lens will often have more detail than that of a 24 megapixel camera paired with a cheap lens. This all comes down to a factor called "Perceptual Megapixels," or "P-Mpix" for short.

Let's get this out of the way now- you will almost certainly never get all of the detail out of your camera sensor that it is capable of. A typical DSLR today has somewhere around a 24 megapixel sensor, but with the kit lenses that come with them, you only get about 9-13 perceptual megapixels of detail (Now you get it!). To get an image with a higher P-Mpix count, you have to use higher quality glass (lenses).

Sharpness can also be affected by factors like shutter speed, aperture, or ISO settings. If the shutter speed is not high enough on the camera, the image can be subject to motion blur. Aperture is also a very large factor in image sharpness. The aperture controls how much light enters the lens, and also the depth of field (the part of the image in focus). At apertures wider than about f/3.2, the image can become unsharp, and at apertures narrower than about f/7.1, the image can be subject to diffraction, which degrades sharpness.