Focal length and portraits

Escaping a bit of the beginners series, a nice topic that always brings a lot of discussion is focal length and flattering portraits, specially for women. Well, as Britney Spears would say “oops, I did it again”. OK, this is not the right meaning, but it’s another experimentation about the topic.

So, the discussion is that short lenses are not flattering for portraits. Longer lenses have more compression, so faces look more proportional and therefore more flattering.

Talking about it with some friends along time and having a science background I decided to do this experiment my way.

First I’ve got a nice model (aka wife 🙂 ) and marked the distance for shooting at 35, 50, 85 and 135mm, filling the frame with my model’s face. So, distance varies, focal length varies, size of the subject in the sensor is fix. I could not do it for shorter lengths (18 and 24mm) because the lens would not focus at that distance. Also, the sensor is a APS-C, 1.6x crop.

The results can be seen below. For short lenses the facial features appear very prominent, while for longer lenses there is more “compression”. 85 and 135mm show almost no difference.

Variable distance and focal length filling the frame at each point.

Variable distance and focal length filling the frame at each point.

The second test was keep the distance fix at the 135mm mark, vary the focal length and not care about how much of the sensor the subject occupies. Then crop the images in a way the subject has the same size. The results (see below) show basically no difference independently of the focal length.

Fix distance, at my 135mm mark, varying the focal length.

Fix distance, at my 135mm mark, varying the focal length.

A third experiment was to keep the focal length fix and vary the distance. Shots were taken with a 50mm at the four marks (actually had to add some canvas to the shot at 35mm mark, since the subject was supposed to fill the frame with a 35mm at that distance).

Here again, distance makes the difference and 85 and 135mm distances show almost the same result, while closer shots present the same behaviour as before, making facial features more prominent.

Variable distance and fix focal length (50mm). Each shot taken at the distance marked before.

Variable distance and fix focal length (50mm). Each shot taken at the distance marked before.

The summary below we can see the experiments above and also comparison between shots at the same distance/focal length. Like how do the shots taken at the 35mm mark, or with a 35mm lens compare to each other.

Shots taken at the 35mm mark (first row), with a 35mm and with a 50mm look very alike, while a 35mm lens at a larger distance (the 135mm mark) looks quite different. The same applies to the 50mm mark (second row). Though 85 and 135mm marks (third and fourth rows) look all very alike, the shots taken with the 50mm seem to show a bit less compression than the others. This can also be an effect of some variation of the light during the shooting.

Horizontally we have each focal length mark. First column is variable distance and focal length (so at the 35mm distance, shot was taken at 35mm). Second column is fix distance (distance for 135mm) and varying focal length. Third column is variable distance and fix focal length (a 50mm). 135mm shots for variable and fix distance are the same, since they are the last distance mark.

Horizontally we have each focal length mark. First column is variable distance and focal length (so at the 35mm distance, shot was taken at 35mm). Second column is fix distance (distance for 135mm) and varying focal length. Third column is variable distance and fix focal length (a 50mm). 135mm shots for variable and fix distance are the same, since they are the last distance mark.

The main conclusion is that the influence of the focal length is none or very small while the distance from the camera to the subject is what really matters.

The physical explanation for that is the relative distances and the angles at which the features (like nose, cheek, chin) are seen in each shot.

At short distances, the size of the features are a considerable fraction of the distance between the camera and the subject. This makes the angles between the features and the side of the lens quite large.

At large distances, the size of the features are negligible compared to the distance between the camera and the subject. The angles between the features and the side of the lens are also very small. This gives the compression effect and makes the image more pleasing and flattering.

Physicists, opticians, expert photographers … please leave your comments!

I enjoyed this experiment! I hope you did it too!

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About Cris Da Rocha

Astrophysicist, DB manager, cyclist, musician and, why not, "photographer to be". Back to enjoy photography after many years ... it's cool. Might share something nice and get something new.
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6 Responses to Focal length and portraits

  1. Matt Butterworth says:

    Many thanks for doing this. Is answered my curious brain’s questions!

  2. Diegonzalez says:

    Great article, thanks for your work !!

  3. Audy Erel says:

    This answer a lot of my question.. Thank you so much 🙂

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