I purchased a Canon T4i with a 18-135mm STM lens. I'm interested in getting a prime lens to take portrait photos of my child. My budget is up to $500.
With an APS-C camera like your T4i, 50mm is a good focal length for a portrait lens. This gives you several decent options:
- Canon EF 50mm f/1.8 II for only around $115. This is a cheap, plastic-body lens, but it benefits from the ease of making lenses in this focal length, and years of history. This is actually my top recommendation, as it leaves you room to buy a flash as well, and that will probably make the most difference.
- Canon EF 50mm f/1.4 for around $340. This has a better AF system and, of course, a slightly faster aperture.
- Sigma 50mm f/1.4 for around $450. More money, but a brand new premium design. I haven't actually used this one but it's getting good comments.
There's a nice review of the 50mm f/1.4 at DPreview, which touches on all three of these lenses.
The Canon 40mm f/2.8 STM is another interesting option. It's also cheap at $150, and optimized for video. The wider focal length makes it more useful as a general-purpose lens and it's still a decent portrait range. If you're looking for a choice with a lot of versatility for things other than portraits, this would be a good one.
You may also consider the Canon 85mm f/1.8 EF USM, at about $420. This is still in a decent portrait range; a little tighter, obviously. While it's not quite like its $2000 f/1.2 big brother, this is a classic and highly-regarded lens.
But, as I hinted above, getting a new prime lens isn't necessarily the first thing to do. You could just keep your existing lens, which covers the portrait range nicely, and add a Speedlite 320EX ($225) or Speedlite 580EX II ($490). This won't necessarily get you the fashionable thin depth of field look you might get from a faster prime, but will let you take more control over the light in your portraits. I'm not really one to discourage buying primes, though, so the 50mm f/1.8 plus Speedlite 320EX makes a very attractive in-budget combo recommendation.
The 50mm f/1.8 almost everyone else recommends is a nice portrait lens but I wouldn't recommend it for kids pictures.
50mm on a crop sensor is a little tight indoors, it's great for a head-shot but very uncomfortable for full-length and group photos (that is, kid doing something cute and kid doing something cute with friends)
The auto-focus on this lens is painfully slow
I prefer something around 30mm, Sigma has a 30 f/1.4 that I heard is nice (but never used myself), Canon has 28mm and 35mm lenses (some of them outside your budget) and there's the 40mm f/2.8 STM that is tiny, got great reviews and is almost as cheap as the 50 1.8
For me, when I photograph my children, I almost always use my kit lens at 30-35mm and the 50mm f/1.8 stays in the bag.
I have the Canon EF 50mm f/1.8 and with the APS-C it is more like an 85mm, so if you are indoors in a small to medium sized room you have to get back way to far, I was at a Pizza Parlor and had to get back about 20 feet to just get a waist up shot which does not work very well when you have others walking in front of you, my next purchase will be the 28mm Canon which converts to about a 42-45 mm full frame lens.
Most of us consider a fast prime a good lower-cost portrait lens. YMMV. But a large maximum aperture lets you have more control over background blur and depth of field, and the Canon f/2.8 zooms cost closer to $1000, so those are out of your budget. But there's also the Tamron 17-50/2.8 (or the VC version), which might work for you.
But if you go with a prime lens, you've got a lot of choices at that price range, so I'd recommend taking portraits with your 18-135, and then looking at the EXIF of the shots you like best, to see where you like to "sit" focal length wise. A tool like ExposurePlot, or using Lightroom's metadata viewing capabilities can be useful for this.
The main candidates to consider, once you have your focal length nailed down, are many and varied, but I'd put forth the following three groups:
"Normal"-ish FoV on a crop
- EF 28mm f/1.8 USM
- Sigma 30mm f/1.4 DC (not to be confused with the much more expensive DG full-frame 35/1.4)
- EF 35mm f/2 (older, cheaper)
- EF 35mm f/2 IS USM (above your budget, but not by a lot)
- EF 40mm f/2.8 STM (pancake lens)
- EF 50mm f/1.8 II (aka "Thrifty Fifty" or "Plastic Fantastic"; cheapest lens Canon makes)
- EF 50mm f/1.4 USM (better build quality, and usability features, a little faster)
- Sigma 50mm f/1.4
Short telephoto primes
- EF 85mm f/1.8 USM (probably the best choice for great head shots with lots of background blur)
- Samyang/Rokinon 85mm f/1.4 (tremendous PITA manual-only lens (manual focus, and manual aperture setting only; no EXIF, only M/Av modes, etc.; but pretty)
- EF 100mm f/2 USM (most folks would probably get the 100/2.8L Macro and double-duty it, though)
- EF 135mm f/2.8 Soft-Focus (weird, but if you like that vaseline-on-the-lens look)