I recently argued with a person on the internet about portrait lenses and I think it's very important to actually know what makes a certain lens good for portrait. First of all, we need to know our location and the space that we require for the shoot and right after that we need to choose the proper lens.
Let's answer one simple question:
Why are some lenses good for portrait and some are just not doing the trick?
The answer is simpler than we think. The secret is not in the aperture, it's not in the size, the weight, the brand or the stabilization... It's all in the aberration, and I mean the distortion of objects (face, body etc.) The less distortion we have in the image the better our models look. This is highly dependent on the focal length and, to some extent, on the sensor's crop factor (click here for more on full frame vs. APS-C sensors). Longer lenses produce images with a lot less distortion. Ideally outdoors I'd shoot with an 85mm or longer lens (if you have a vario lens make sure to keep it zoomed at over 50mm) to steer clear from any distorted faces. My big love however is the 50mm prime lens that gets me the results I need. It's small and it's perfect for outdoor portraiture.
However, if I want to shoot in a studio a vario lens is required. Some people who rarely do studio shoots will go ahead and start proposing prime lenses for studio portraiture but people who know the trade will tell you prime lenses are pretty much useless between four walls. The reason you need a good vario (basically anything between 18 and over 100mm would be nice) is that studio shoots take a certain amount of time that can't be expanded too much (studio hours, models, make-up artists, stylists and what not) and we want to get the job done so shooting with a prime lens means moving lights back and forth as well as setting their strength over and over again. And all this because if we want to zoom in on the model with a prime lens we have to take a step forward and drag the lights (all front lights that would hit our back for standing in front of them) with us instead of zooming in with a vario lens and taking the framing we want.
By using vario for portrait shoots in closed spaces we solve many problems and make the shoot possible. Just make sure you're not too close to the model at a smaller focal length to avoid distorted images. Zoom in and out using the vario and don't zoom out all the way because it will be a disaster.
A good vario lens will get you where you need to be at the studio but nothing beats the bokeh of a prime lens when shooting outdoors. This is one of the main reasons people get a nice 50mm prime lens (apart from its low price of course). You have lots of space behind the model and lots of space to move around and take angles and go around outdoors so this is the best option for the case. Indoors, however, you need a sharp vario with as little aberrations as possible to cover different framing from one line of shooting without moving the lights too much. You will be using aperture values between f5.6 and f13 on a single-color background so forget about the bokeh of the 50mm.
Write your questions below and I'll be more than happy respond. For more on lenses click here.
All the best,