Bob Evans wrote:
If I have a 50mm do I Need a 85mm for my T3i, to get best portraits/
I use both for portraiture with crop sensor cameras, same as your T3i. (Actually, on Canon APS-C cameras like ours the 50mm and 85mm lenses give the same angle of view as 80mm and 136mm would on a full frame camera. "Ideal" portrait lenses!)
On your T3i, 50mm and 85mm represent the traditional "short portrait telephoto" to "long portrait telephoto" focal length range.
In my opinion, neither is "better". They serve somewhat different purposes.
50mm is great for indoors, full torso portraits, even couples and/or full-length portraits if you have enough working space. You need to be careful not to get too close with a 50mm or you'll start to see perspective distortion, so it's less useful for tight face shots.
85mm needs more working space, so may be less useful indoors, but is great for tight face shots without getting too close, which helps avoid distortions. It's also good for looser portraits from a bit of distance when there's adequate working space, which might be a bit more candid.
Recently I've been carrying a Tamron 60mm f2.0 Macro/Portrait lens at times (in place of three lenses: 50mm, 85mm and an f2.8 macro). It uses a micro motor, so is not nearly as fast focusing as my Canon USM lenses and isn't really up to fast sports/action shooting. But it's fine for portraits and macro. It's f2.0 aperture is better than almost all other macro lenses, which are f2.8 at best. That's within 1/3 stop of my 85mm's f1.8... And I'm usually stopping down my 50/1.4 to f2 or f2.2 anyway. The Tamron 60mm is a "crop only" lens, reasonably compact and internal focusing, great image quality and a useful alternative so I have less to carry around some of the time.
This is not to say that both wider and longer lenses can't be used for portraits. They can. But they need to be used more carefully.
There are reasons the above telephoto range is popular for portraiture. Anything wider has greater risk of various perspective distortions that can be a problem... or humorous. Big noses, tiny ears, plus anamorphic distortion of anyone or any body part near the edge of the image. Those might make people laugh... if they aren't pissed off at you. That said, a 35mm, 30mm, 28mm or even 24 or 20mm (on a crop camera... 50mm to 30mm on FF) might be used for certain types of portraits, such as "environmentals" where a lot of the person's living or work space is included in the image.
Longer teles require a lot more working space and have a subtle "perspective flattening" effect. It can be a good thing. Longer teles: 135mm to 200mm on crop cameras (200 to 300mm on FF)... are popular for fashion photography, essentially another form of portraits. You just need a very big studio or lots of room on location to use them.
With kids and pets, a zoom can be handy! I usually use a 24-70/2.8 on crop sensor cameras (or a 70-200mm on full frame). Still, these zooms are only f2.8, at best... and are rather large, heavy, intrusive lenses. So whenever possible I still prefer the smaller, faster primes.