What is a good Canon lens to take portraits?
I have a Canon Rebel T1i camera. I am thinking of buying a Canon EF 50mm f/1.8 II lens for portraits. Is it the right lens for portraits? If not what other lenses would you recommend.
The Canon EF 50mm f1.8 II is a great "starter" prime lens in my opinion. Perfect for portraits when mounted on the Rebel due to the crop factor conversion. The lens itself feels really cheap and was cumbersome to manually focus for me personally; I found the focusing ring too narrow. The bokeh is good but quite busy due to only 5 (non-rounded) aperture blades. Despite all this, the images this lens yields are good and sharp.
The 50mm f/1.8 will take fine portraits, however don't assume that the 50mm is the only length at which a lens is suitable for portraits. Nearly any lens longer than 35mm can be used to good effect, and the longer a lens is, the more "flattened" the distances involved become (which can be handy).
I've used various focal lengths to take portraits, ranging from 35mm to 200mm. It all depends on what you want creatively and how far away (or close) you need to be from (to) your subject. (I mention this because some subjects have a very large personal space -- it may be better to use a longer lens to avoid infringing upon this space and making them uncomfortable.)
For candids, distance is often key. I've made some of my best candid shots at focal lengths of more than 100mm (and often 150 or 200mm). This is because the subject often doesn't even know the image is being taken.
The 50mm f/1.8 is practically disposable, both due to its cost and cheap make. In one way it is nice, because if it is broken, it isn't expensive to replace. However, if you want something with better manual focus and a better make, look at the 50mm f/1.4 or either of the 85mm variants. (85mm might be a little long, depending on what your intentions are.)
Don't forget that with a T1i, you have a cropped sensor. This means a 50mm lens gives the same effective view as 85mm on a full-frame sensor. Essentially this means that in short spaces you may not have the flexibility to capture what you want, but in normal spaces you should be fine.
I would recommend that you also take a look at the 50mm f/1.4. As far as I can understand from reviews, apart from the larger aperture, it is also of better build quality. Don't know what the price difference is though.