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Optical zoom leverages the physical change in a lens to adjust the distance between the camera sensor and subject, whereas digital zoom uses magnification technology to enlarge an area of an image, thereby compromising the integrity of the picture by cutting down on the megapixels.

Unless it's a very expensive full-frame model, all digital SLRs will have a focal length conversion (also called a field-of-view crop factor) to deal with. Basically you have to re-train your mind to think in digital SLR, rather than 35mm terms. Let's imagine this scenario. You grab your old Canon Rebel film camera and take a picture

Some digital cameras can adjust for lens focal problems. Sometimes the focus was sharp enough but other times, especially at f/2.8 (limited depth of field) the shots were soft. This was a film camera and no local calibration was possible. 

Shutter speed is the amount of time the shutter allows light onto the CCD. The shutter speed is measured in seconds (or fractions of a second for most common pictures). The slower the shutter speed, the more motion is recorded by the camera. A tripod might be needed to use slower shutter speeds without blurring the picture. 

UV filters are practically useless (image-wise) on DSLRs since digital sensors are not nearly as sensitive to UV light as film. So don't spend $150 on a "premium UV filter" if you're shooting digital. Just grab a $20 one off amazon and use it as a lens protector. 

Generally photographers put UV filters on DSLRs for the larger purpose of protecting their lenses. Lenses can cost hundreds or thousands of dollars, whereas UV filters are generally less than $40, and sometimes less than $10.