what is the names for them?...lol.. i'm flying on the same boat as this person, but just not sure if i should get the 1.8 or the 1.4 for 50mm lens, i've got a T1i, but it's the plastic build quality that's turning me off, will it still be TACK SHARP as the 1.4?
if you mean the names for the 50/1.8, it's just Canon EF 50mm f/1.8 and EF 50mm f/1.8 II. the II is a cheap plastic one, the original is a cheap metal one.
i seee.. so your saying, that, if your camera isn't a full frame, and you put a 50mm on it, it'll look like an 80mm lens was on it?..i've got a T1i, and i'm using the lens kit 18-55, does that mean it's also zooming in more than it's supposed to?
forget about all this equivalent crap. focal length is fixed - a 50mm lens is 50mm on 35mm, medium format, large format, APS-C, 4/3, or whatever other camera format you can think of. this information is useless to you unless you are familiar with 35mm cameras.
50mm is a standard lens on 35mm. on a T1i, which is APS-C, a 30mm lens is standard, and 50mm is a short telephoto. a standard lens is much more useful as a general-purpose lens than a telephoto, especially as your only prime.
so if you want a prime, it's best to buy a Canon 28/1.8, Canon 35/2 (which is actually a long standard or very short telephoto, depending how you look at it), or Sigma 30/1.4 instead. the Canon 35/2 is the cheapest, around $250 used. I would buy that until you can afford a Sigma 30/1.4, assuming you like the field of view.
which one is better the 50mm 1.4 or 50mm 1.8? What is the difference between the two?
I disagree with Edge here. I've had both - two 50/1.8's, one refurb and one used, on a 30D and 5D, and a 50/1.4 on the 5D. I've had no issues with AF accuracy with the 1.8 on either body, though admittedly I rarely used it on the 30D. you just have to know what to focus on in poor light.
sharpness-wise, they are similar...pretty much everywhere. most 50/1.4's exhibit halation at f/1.4, making it softer than it should be. I don't think it's usable unless at f/1.6, when the halation goes away.
the 50/1.8, with its cheap optics and 5-bladed aperture, has distracting out-of-focus blur. on 50/1.4 the out-of-focus blur is still distracting (i.e. bad bokeh) when the background is busy or contains a lot of specular highlights. if the background is relatively clear, it does better than the 50/1.8. other than that...both are pretty similar, optically.
the 1.4 has a better build and a USM motor, but it's AF speed isn't much faster (if at all) because it's the same motor, just silent. I didn't think a better build for marginally better optics and 1/3 stop (f/1.8 - f/1.6) was worth the money, so I kept the 50/1.8 until I could afford a Sigma 50/1.4.