Why should i buy prime lenses? and what is a good one?

the nifty fifty, or so it's nicknamed, is a REALLY sharp and REALLY cheap canon lens,

the EF 50mm f/1.8 can be had for around $90 new on amazon, or $50-80 on craigslist.

the 50mm becomes 80mm EFOV on a crop body which makes it a nice portrait lens.

I use a few older pentax prime lenses on my canon (through the use of an adapter), I actually like the prime manual focus lenses on a digital body. Manual focus and not being able to zoom makes you really think about the shot before you take it.

A prime lens is usually anywhere between f/1.4 and f/2.8 on the max aperture so it is a brighter and faster lens. Because it only has to be good at one focal length they are smaller, lighter and less expensive than an equivalent quality high speed zoom. The IQ is also usually better throughout the frame than a zoom.

That said, there are some very nice zooms out there and they may have their place in your camera bag. If I were traveling I would definitely want a good zoom if I only took one lens along.

I traded in my Nikon 18-55 for the 35mm f1.8 lens. The lack of zoom seems like it would be limiting, but it really isn't, at least for me. What limited me was the slow 3.5-5.6 aperture of the kit lens, as I do lots of low light photography. Sometimes, I miss that 18-28mm range, when I am in a cramped room. But that's it.

Along with my 35mm f1.8, I carry a 55-200mm tele-zoom.

You might find that 50mm is a bit long, though for the smaller sensor. As others have said, it's about 80mm in 35mm terms. I don't know if Canon has a 35mm lens (or something close to that) available for a normal lens on their smaller sensor DSLRS, but I'd look for that.

If you are planning your second lens,your other option could be a telephoto zoom 70-300mm.

In prime, since you have 18-55mm , you can think of 85mm/f1.8.

Prime lenses are sharper than zooms as a rule. They can also be better at controlling chromatic aberrations. They are also more often constant low aperture (many f/2.8 or f/4) for low light situations or for capturing fast motion.

I was never a believer in prime lenses. But it totally depends on what you need the lens to do. I am a portrait guy. I knew even though it seemed like a limiting factor, I ought to do it based on what everyone else was doing. So I did it. I got a 50mm prime. It was faster for sure. Better quality, not necessarily. I just got a Tokina 100mm prime and its amazing. I'm sold on it. Its a shade long for what I have right this minute, but when I make my studio bigger, it will be perfect. So right now I'm shopping for a 85mm f/1.8 since I can't afford the f/1.4. If you have situations that you think a prime would work well, buy one. Don't feel pressured into buying one. As far as quality goes, I think my Nikkor 18-135 is the sharpest lens I own, even for portraits. large apertures and fast shutters mean nothing to me when I'm in the studio with 4 or 5 strobes firing at once. Buy the best glass you can afford, but make sure its something that you're going to use and not just take up space in your bag.