The answer is dependent on what type of portrait you’re shooting. The main framings for portraits are headshots, half body, and full body.
For headshots I like the 70-200mm lens. These lenses are the best for this purpose because of telephoto compression. Compression flattens out the subjects facial features and makes the image more appealing. When you’re really close to someone’s face a wide angle lens, even a 50mm, can start to introduce curvature due to perspective lines.
In the range of a half body shot I like 85mm f/1.4 a lot, but since it’s further back you can also start using a wider lens like the 35mm.
Check out the following portrait taken with a 35mm lens to see what I mean.
When using a 35mm for portraits you just need to be careful about how you frame the shot to avoid distorting the subjects face and body too much. Most people don’t like to see their faces squished up oddly regardless of how cool of a picture you might have taken!
It’s a touch call for me which lens is better for half body portraits, the 35mm or the 85mm. I think I have to choose the 85mm just because it’s so easy and lets you blur out any background to look epic, such as in the below shot.
For full body portraits I like 85mm the best again. Shooting full body with the 85mm you don’t have to stand too far away but you still get lots of separation with the background. The following full body portrait was taken with an 85mm lens. Fast 85mm lenses are expensive but if you’re a serious portrait photographer you should probably own one of these and use it often.
An 85mm f/1.4 is just about equivalent to a 200mm f2.8 in terms of background blur at the same framing.
Here is another shot taken with a 70-200mm lens at f/2.8 and 92mm.
While both a 85mm prime and a 70-200mm f/2.8 will get you very professional looking results, when it comes to 90% of portrait scenarios the 85mm prime is the winner. The 70-200mm is a very good lens but isn’t as good as the 85 when it comes to controlling backgrounds.
The biggest advantage of the 70-200’s is typically that they’re more flexible with their MFD which can allow you to stand close enough for a true headshot. Many 85mm primes have limited MFD that make them unsuitable for headshots. In other words, headshot photographers should probably stick with the 70-200.
The 35mm is also an interesting choice for more dynamic shots with more environment in them.
Another option that someone is sure to mention is the 135mm focal length. 135mm is great but its a bit of an in between focal length. It has a traditional following for the purpose of portraits. I would rather just us a 70-200mm. If you want to flatten the scene, a 70-200mm is better and that to me is the main reason to choose the 135mm over the 85mm. As for the bokeh from a 135… it has a lot if set to f/2 or faster. You’ll probably end up stopping down because the fast 135’s give too much subject isolation. The one thing a 135mm will do better than just about any other lens is sharpness.
If you have to pick one as portrait photographer, choose the 85mm. Most people will find using an 85mm easier than using the 70-200mm. The 70-200mm requires more knowledge while it is easier to shoot with 85’s by feel. So if you’re just getting started, go with the 85mm, it will help you generate successful shots having a fixed focal length and you can later move on to a zoom if you want to.