What is the Best Focal Length for Portraits?

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It's commonly said that the best focal length for portraits is 85mm to 135mm.  That is often true, but what's the underlying rationale for it?  What if the subject is a child?  What if it's a group portrait?  What if you wanted to include the environment in the background?  The truth is there is actually no ideal focal length for portraits.  Instead, there are three factors that you need to keep in mind.  Hit the jump!

DISTANCE VS. FOCAL LENGTH

First, a subject's appearance and facial proportions are affected by perspective, which in turn is dependent on the distance from the camera to the subject, not the focal length per se.  Of course, there are typical compositions for headshots, which is how certain focal lengths were associated with portraits.  However, ultimately, what you need to consider is the distance to the subject.  This is more useful to know when using a composition other than a headshot for one person.  The best focal length would vary if the subject is a child or a tall adult, or if you wanted to get a full body shot instead of a headshot, or if there are more people, or if you wanted to include the background in an environmental portrait.  But in each case, what controls the subject's appearance is the distance from the camera to the subject.

THE INTENDED EFFECT

OK, now that we know it's actually the camera-to-subject distance that we should be thinking about, what is the best distance for portraits?  Again, there is no single best distance.  The best distance depends on the effect that you want. 

In a study published in the Journal of Vision, scientists showed photos of ten men and ten women to the participants of the study.  The portraits had the same scale (the same apparent size) but unbeknownst to the study participants, the portraits were taken at different distances.  The participants rated the portraits according to certain qualities such as attractiveness.  The participants' answers were then correlated with the distances at which the portraits were taken.  The scientists found that the camera-to-subject distance influenced different qualities of the portrait subjects:

• close distance (56cm / 1.8 feet): "more benevolent (good, peaceful, pleasant, approachable)"
• intermediate distance (124cm / 4.1 feet): more attractive
• larger distance (400cm / 13.1 feet): "more impressive (smarter, stronger)."

The best distance therefore depends on what impression you and your subject want to create in the portrait.  Do they want to look more benevolent, more attractive, or more impressive?  You can then choose the distance accordingly.

THE SUBJECT

Finally, you should consider the subject's facial proportions.  Subjects' faces can be wide or narrow, and size and shape of their noses can vary.  Shooting at a closer distance has the effect of making a face appear more narrow, or can make a nose appear longer, and vice-versa.  We can choose the distance that complements the subject's facial proportions.

CONCLUSION

There is no single best focal length for portraits.  Instead there are three factors to consider: First, you should consider the camera-to-subject distance (not the focal length). Second, you should think about what quality you want to emphasize in the portrait: their benevolence, attractiveness, or impressiveness, then choose the distance accordingly.  Finally, you can adjust the distance to complement the subject's individual facial proportion.