Good Studio lens for Portriats ( Canon )

Im guessing you are just using hot lights as opposed to strobes since you mentioned that the studio can be bright if need be? Or maybe just window light? If so, you are going to need something with pretty wide aperture of at least 2.8.
Also, how big is your studio? I find the 70-200 2.8L is lovely for indoors, IF, your studio is at least 15-20 feet long (however, even at that you may not get the full body). Other wise something like the 24-70 2.8L may be the next best option.
John

What type of body are we talking about here? FF or crop?
Typical portrait lenses: 85mm for FF, 50mm for crop - how much do you want to spend? The 85 1.8 is reasonably priced, the 1.2 version is legendary and costs a fortune. Same for the 50 - can be had as cheap as $85 for the 1.8, or the better built 1.4 or the very expensive 1.2. A fast zoom covering that range is another option - but we need the type of camera first.

I use the 24-70 most of the time, on a 1.3x body. This is from a recent shoot for a magazine cover, at 32mm. I have found through practical application that the "portrait lens" hype is way overblown.

Olympic Champion, Copyright 2010 Jeff Spirer

Disclaimer, I know nothing about Canon. Recently I've been using my old 1980s Tamron SP 28-80 on my Nikon crop body for many things. At first I just pulled it out because I wanted to test that range on my croppers to see if I might want to invest in a new fancy VR 2.8 around that length. Funny thing is I still am using it and no longer want to buy anything, so I'm with Jeff on this one. Hey, it still works nice and it's free.... That being said, I do use the small 50 1.8 Ais and 85 1.8 AF a lot so those are a great pair too but you probably want some newer Canon ones ;).

On my Olympus DSLR I like an old Olympus OM 50mm f:1.8 manual lens...with the Olympus format, that equals a 100mm focal length on 35mm; gives great results with a wide stop. If you have a Cannon with a 1.6 equivalency a 50mm lens from a 35mm camera will give you the same field of view as an 80mm lens...a good length for portraits. I think I've read that the Cannon DSLR's will take the old Cannon 35mm lenses without an adapter, but I'm not certain of this...some of these other guys will be, though.

For Canon i prefer the 50 and 85mm, if you have the budget go with the L versions, if not the regular lenses are quite capable. The 45+90 mm TS lenses are a nice zinger if you looking for effect/more control. If you don't mind manual focus definitely consider the Zeiss lenses.
I just wouldn't mix them for appearance reasons (color, contrast rendition).
And if you want a zoom, the 24-70 and 24-105 are quite capable lenses (see Jeff's photograph 32mm x1.3 factor= 41mm on a 35mm full frame, the perfect theoretical "normal" lens), i feel they distort a bit more in the corners than the fixed lenses and i tend to avoid them, but there's obviously an economic argument for it.
I tend to shoot close ups with the 85 mm to keep a little distance form my subjects and everything else either with the 85 mm, which allows me to move in and out quickly or the 50 mm for more effect.
I would respectfully disagree with the choice of the 70-200, i just got the new version and it's a beast, 3 pounds on top of my 1Ds is a challenge i can not meet when shooting handheld for an entire day (and yes, i do push ups and work out with 25 pound free weights, thank you).

twenty four seventy

Camera body/system currently used/owned, studio size, type of lighting available, desired effect/outcome. All these will affect what lens you should get... there is no singular solution, only YOUR solution.

Historically, the portrait lens is softer. This stems from the classic view that portraits are planned , eyes in focus and ears and nose just a tiny bit blurred. To accomplish you will discover that large lens openings are favored because they wipe out depth-of-field. Accessories to soften abound. These take on a form that resembles filters. They soften by disturbing the light path of the imaging rays. Other methods are to shoot thru a silk stocking or smearing the margins of a filter with Vaseline or body oil.

Likely, the most important ingredient is choice of focal length. As you know each frame, size has dimensions height, width, and diagonal. For technical reasons the "normal" lens for any frame size is one that that approximately equals the diagonal measure.

For example, the full frame 35mm measures 24mm by 36mm, the diagonal works out to 43mm. When a 43mm is mounted, the angle of view is 53° (considered "normal"). Because this is a unusual value, opticians generally bump up to 50mm which delivers an angle of 47°. Now the compact digital frame is smaller. It measures 16mm by 24mm with a diagonal of 29mm. Note 43 ÷ 29 = 1.5 the source of the 1.5 magnifying or crop factor. One could also say, the compact is smaller, 66% of the size of a full frame. When the compact is operated with a 29mm the angle of view is 53°. Note this angle is widely accepted as the human experience.

How can these facts answer my question about the best portrait lens?

Portraits are reproductions of the human head. We all have a preconceived idea of what we look like and this is derived from the view we see every day in makeup or shaving mirror. A portrait that delivers this perspective is best achieved when the focal length used is about 2.5x the diagonal. This is just a rule-of-thumb and not engraved in stone. However if you dismiss out-of-hand you will likely experience reduced success. Adherence to this rule-of-thumb mitigates moans and utterances like "the camera lies" or "I don't photograph well".

OK, the portrait lens of choice for the full frame revolves around 105mm or about 2.5x the diagonal. For the compact, this works out to around75mm. Why? Using a lens about 2.5 times longer than "normal" forces the photographer to step back, away from the subject. If you ignore and work-in too close, the nose reproduces microscopy too big and the ears microscopy too small. These tiny distortions induced to the very familiar face, a feeling of abnormal. Hollywood uses 3x normal when making close-ups for the big screen.