Prime Lens is lens that has a fixed focal length, example: 50mm
Zoom Lens is lens that has a flexible focal length, example: 18mm – 55mm

Prime Lens

1. Quality

The inside build of a Prime Lens is simpler than a Zoom Lens, since they don’t have a lot of moving parts like zooms, the glass inside of a Prime Lens is very precise. It has the ability to produce clean, crisp and precise shots.

2. Price

Well, nowaday Zoom Lens also improved on the quality, but you would be spend more cost on same quality Zoom Lens instead of Prime Lens. Thus, you can get reasonably priced Prime Lenses with wide apertures.

3. Weight

Simpler build, lighter weight. Ya, Prime Lens will lighter than Zoom Lens, it is easier to carry, and may be it will slightly prevent your hand shake while taking photo.

4. Speed

Prime Lens is faster than Zoom Lens in terms of aperture.

Zoom Lens

1. Flexibility

This is the key selling point of Zoom Lens, with it’s variable focal length, you may just need one lens to coverage all the focal length.

2. Price

You need one Zoom Lens to coverage the focal length, while you need a lot of Prime Lens to do so. So this is the price comparison between “one Zoom Lens” and “N number of Prime Lens”. The N number is depends on your demand.

3. Portability

Same reason to price, it is easy to carry one lens rather than three or five lenses.

Conclusion:

Prime Lens or Zoom Lens, it totally depends on yourself, depends on what you actually need. What type of picture you wish to capture by your DSLR? (portrait, sports, landscape or other) How many budget do you have? What you want?

article references:
a) http://digital-photography-school.com/prime-vs-zoom-lenses-which-are-best
b) http://www.digital-slr-guide.com/prime-and-zoom-lenses.html

For DSLR beginner, we always see the lens with the number such as 16-35mm, 24-70mm, 70-200mm. After that I know that’s call ‘Focal Length’, but as a beginner, i don’t even know what is focal length.

What is Focal Length?

According to the description from wikipedia, the focal length of an optical system is a measure of how strongly it converges (focuses) or diverges (diffuses) light.

The picture above i “borrow” from Understanding Camera Lenses. From this picture, we can know that:
- as the focal length shorter, as the angle of view wider
- as the focal length longer, as the angle of view narrower

Angle of view wider, means that the object can be focus is nearer. So normally those lenses with short focal length (below 35mm) is for wide angle use, focal length with 35mm to 70mm is normal use (example: portrait), and the 70mm and above is for telephoto (example: sports).

For more information about DSLR Lens, may refer Understanding Camera Lenses.

Source:http://www.the-digital-picture.com/Canon-Lenses/Canon-Lens-Selection-Introduction.aspx

You are being diligent. You are being responsible. But the more you research your lens purchase, the more confused you become. There are a huge number of Canon lenses available and a near-infinite number of Canon lens combinations available.

Well, you can relax. You are certainly not the only one that is confused. And the good news is that, most likely, there is more than one Canon lens that can adequately accomplish your goals.

I will attempt to make some recommendations for lenses for popular photography subjects. In the event that you select the wrong lens, most of the vendors supporting this site will let you return it in new condition for a refund/exchange within their reasonable return policies.

First, I have a couple of questions to ask you …

How much is the right lens worth to you? How much are you willing to spend to capture excellent images of your children before they grow up? How much are you going to make using the lens as a pro? What are you going to lose if your lens does not perform up to expectations? How long do you expect the lens to last? How hard are you going to use the lens? In what weather conditions do you expect to use the lens?
Do you need a Zoom or Prime Lens?

What Focal Length do you need? Getting this question wrong can, in some situations, render a lens nearly useless to you, regardless of how awesome the lens’ image quality is.

What Maximum Aperture do you need to stop camera shake or stop the action?

Now keep in mind how much you have spent for your awesome new DSLR body. You are going to be wasting much of that money if you put an inferior lens on it.

Find the recommendation category closest to your need. Then read the reviews for the suggested lenses (and other similar lenses) to make your decision.

A photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically. While in principle a simple convex lens will suffice, in practice a compound lens made up of a number of optical lens elements is required to correct (as much as possible) the many optical aberrations that arise. Some aberrations will be present in any lens system. It is the job of the lens designer to balance these out and produce a design that is suitable for photographic use and possibly mass production.

There is no major difference in principle between a lens used for a camera, a telescope, a microscope, or other apparatus, but the detailed design and construction are different.

A lens may be permanently fixed to a camera, or it may be interchangeable with lenses of different focal lengths, apertures, and other properties.

source: Wikipedia – Photographic lens