I am very new to photography but am looking to upgrade from my kit lens. I have a canon T2i. I am looking for a lens that would be suitable to taking pictures mostly of my family and children indoors and occasionally outdoors. I am in no way a professional and have no intention of taking that kind of quality but I would like our photos to be better. I was looking at getting a portrait type lens perhaps the EF 50mm f/1.4 USM. I am not sure if this is the right direction for this type of photography or if I am just better off with my kit lens. Any suggestions would be greatly appreciated!!
For family and children I like to use the EFS 18-135, it's a "kit-quality" lens but its relatively inexpensive and 18-135 exactly covers any reasonable composition at parent-kid distance.
It's not a fast lens so I also use the $70 YN-465 flash, it's a TTL model so just point it at the ceiling and you have the right amount of nice soft light in any indoors situation.
For my family photos the 18-135 is good enough, it doesn't have the image quality of the 50mm or other high end lenses but it's still good enough (much better than any point and shoot I've ever seen) - for professional and studio work I would use something else but for the kids it's right in my price/weight/quality "sweet spot".
I don't recommend the 50 f/1.4 because 50mm (on a crop sensor) is a bit to long indoors (for me personally most of the photos I shoot of the kids are around 30mm) and it's difficult to photograph children at a wide aperture, the depth of field is very thin and children just don't stop moving so you'll get photos where the child is out-of-focus (so you can't really use the f/1.4 to shoot in low light).
As @Nir says, the 50mm F1.4, which is a great lens and very inexpensive, is a bit long for indoor work on a crop sensor camera.
My replacement for my kit lens is the EF-s 17-55 F2.8. Its about $1100. Its a great lens, very sharp, and fast. The 18-55 F3.5-5.6 kit lens quickly goes from F3.5 down to F5.6 and that is slow. The constant F2.8 is massively faster, which is great for both typical indoor lighting, and for giving a nice out-of-focus for your depth of field.
I have both the 50mm F1.4 and the EFS 17-55 F2.8, Both are really nice lenses
EF 50mm f/1.4 is not too long for portrait photography, it's a great lens and you would be amazed by the result.
But it seems what really need is a kind of all-around lens, indoors, outdoors and portraits?! so you diffidently need a zoom lens not a prime.
You didn't mention your budget, so I would give you some general advice.
You already know that you need fast lenses.
Take a look at this list, it's sorted by price from low to high.
Look up the lenses on Flickr to see their sample photos.
And read lens reviews, you can find many reviews on photozone.de
You specifically said "portrait" in your question, so people are going to assume that you're taking pictures mainly of people's faces. For that use, a 50mm lens is a great choice for your Rebel T2i. Think about what you see when you look at a photo taken with a wide angle lens... it tends to magnify the center of the image and compress the edges. Here's an extreme example taken with a fisheye adapter, and you can see that the subject has an enormous nose. For that reason, many people prefer a to use a longer lens for portraits. For example, they might use an 80mm lens on a full frame camera. To find an equivalent lens for your crop-sensor camera, multiply the focal length by 1.6. 50 * 1.6 = 80, so a 50mm lens on your camera will give you an effect similar to an 80mm lens on a full frame camera.
I bought the EF 50mm f/1.4 for the same reasons you're considering: taking pictures of people, mostly kids, with a Canon Rebel XT. I chose the f/1.4 partly because the reviews I read said it was better made and partly because I figured the wider aperture would give me a little more flexibility -- it's always good to use the fastest shutter speed you can muster when kids are involved. All that's true -- it certainly feels like a well-made lens, the wider aperture is nice, and the lens is super sharp. But it comes with a little caveat: when you shoot close up with the lens wide open, you get a ridiculously narrow depth of field. I've got all kinds of pictures of faces where the nose is perfectly sharp and the eyes are a bit out of focus. It's my fault, not the lens, and it's not a bad effect when you get the eyes in focus instead of the nose. I'm just saying that if you still feel like a rookie, and especially if you do much shooting in the automatic modes, you might actually be happier with the EF 50mm f/1.8 for the time being.
The answer depends on your budget, and what sort of portraits you would like to take. Traditional head-and-shoulders portraits would generally be taken from 50mm and up with an APS-C camera (corresponding to 80-85mm and longer on full frame), to avoid unwanted distortion of facial features. This general range is considered to be nice for such portraits because the perspective is still somewhat intimate; much longer lengths (say, 135-200mm on APS-C) can still result in some nice portraits, but would flatten the features much more, i.e. look a little more like a cardboard cutout, decreasing intimacy even if a viewer couldn't quite put his or her finger on why, or even if it weren't noticeable due to a lack of easy comparison.
However, the inquiry does not end there-- wider shots involving more of the surroundings and background are often called "situational" or "environmental" portraits, and on APS-C many of those are well taken at 28-35mm or even wider (as are many photojournalism-style shots that might also qualify as portraits). I've even seen some a few fine portraits taken with extreme wide-angle fisheye lenses, although that sort of effect can of course be overdone.
Another consideration is whether you want the convenience of a zoom but still better subject isolation and low-light performance than your current kit lens. f/2.8 is still noticeably better for these than f/4-f/5.6, but still nothing near primes for general use in people for subject isolation (especially for single subjects) and low light. You might think that a stabilized f/2.8 zoom will do all right in low light because of the stabilization, but in reality those lenses are still fairly slow for portrait shooting because people move; even for relatively slow movers you will lose a lot of shots to subject movement if you dip much below 1/60-1/80 of a second or so. This means that with an f/2.8 zoom you will wind up really jacking up the ISO and still probably needing to supplement with noticeable flash. However, a lot of people do swear by their f/2.8 zooms, and if you just want a noticeable increase in quality while preserving as much convenience as possible, you may wind up happy with one as well.
I would also recommend investing in a flash that has a head that can swivel and bounce. You don't have to spend a ton of money to get one that's decent, especially since if you do your job right with a photo, you don't need a lot of flash power at all, just sometimes a slight supplement to the ambient light. I recommend the site strobist.com for learning more about techniques to use with a flash.
My own personal journey has involved moving to wider primes. For a long time my favorite lens for portraits on APS-C was actually a 100mm prime, which today is quite long for my style of shooting, and which of course would best be used outdoors most of the time. Today I would tend to use primes in the 24-35mm range on APS-C, partly because of the greater convenience in tighter indoors quarters, and partly because I don't shoot close-up face shots so much any more. (Incidentally, you can use a 50mm just fine indoors, just won't be getting much more than the face in tight quarters.)
Keeping all of that in mind, and without knowing your budget, here are some ideas:
(I have eliminated f/2.8 primes from consideration, even though I like some of them-- because especially on a budget, you are probably better served with one of the zooms below. I have also not recommended any non-autofocus primes, though there are some very good deals to be had in that area. Lastly, I've excluded anything over about $1,000 US from consideration, since you are probably on at least somewhat of a budget if you're shooting only a single APS-C camera.)
Canon 17-55mm IS, Sigma 17-50 OS, Tamron 17-50 VC, etc. (These are decent all-rounders, though you won't get massive improvements in subject isolation or low-light portrait ability with them, as noted above.)
Sigma 24mm f/1.8 (check the autofocus; some users like it, and a good copy is optically decent)
Sigma 28mm f/1.8 (check the autofocus; some users like it, and a good copy is optically decent)
Canon 28mm f/1.8 (somewhat unlovely bokeh; decent build and autofocus; a decent all-rounder; though not stunningly sharp wide open, starts getting better rapidly as one stops down)
Sigma 35mm f/1.4 (superb optically and much cheaper than the L, but still pricey; reported to have accurate AF)
Canon 35mm f/2 (optical performance so-so wide open, but not bad for the price; very small and light; loud/buzzy autofocus)
Canon 35mm f/2 IS (very nice optically, and stabilized to boot; good build and AF; still somewhat pricey)
Canon 50mm f/1.8 (not as good as the f/1.4 version optically and in terms of autofocus, but an excellent cheapo addition to another prime of a different focal length)
Canon 50mm f/1.4 (superior to the f/1.8 optically and AF-wise; full-time manual AF; sadly somewhat prone to breakage due to the AF clutch mechanism)
Sigma 50mm f/1.4 (a fair bit superior optically wide open compared to the Canon 50mm f/1.4, though the Canon wins on sharpness stopped down; better built than the non-L Canon 50mm primes; many users have experienced AF problems, but if not you will have a stunning lens-- so buy from a place with a good return policy and/or try before you buy)
Canon 85mm f/1.8 (superb optics and build for the price, though prone to a bit of fringing wide open; lightning-fast AF)
Sigma 85mm f/1.4 (optically superb; some reports of AF issues, but less than with the Sigma 50mm f/1.4; buy from a place with a good return policy and/or try before you buy)
Canon 100mm f/2 (superb optics and build for the price; lightning-fast AF; considered by some to be a poor person's 135L)