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Right focal length choice for the Face portraiture
The widespread stigma of "portrait lens" sometimes needs some clarifications. Different lenses shall be used for different kinds of Portraits. The topic of this article is the person's face portrait and the lenses which are recommended or are not recommended for shooting of such picture.
Person's face portrait is a picture / photo where most of the frame covered by human face.
So we will try to answer the question: which lens (or which focal length) is suitable to capture the face portrait and which lens is not recommended for this purpose?
At the beginning we should say a few words about reproduction of objects by lenses with different focal lengths.
The above photo (Wikipedia) shows that the lenses with different focal length represent different proportions of objects positioned at the foreground and background.
It look like wide angle lens moves background away(makes the objects in the background to look smaller), and objects placed in the foreground makes to look bigger.
In opposite long-focus lens pulls foreground back (compresses perspective), thus shorten the visual distance between objects in the foreground and the background.
To understand this effect better a “trick” should be noted: to keep the size of the foreground object the same, pictures were taken from the different camera-to-object distances. That means shooting with wide angle lens was made from shorter distance to the object. This is a true root cause to different objects display size.
If you want to shoot a face portrait without a post processing crop you will need to position the lenses at the different distances from the face for different focal lengths.
As an example some pictures were taken with a set of lenses with different focal lengths (used lenses are: Panasonic 20mm, Vivitar 28mm, Minolta 50mm, Minolta 85mm, etc.). Since used camera - Olympus E-PL1 has a crop factor of x2 - all focal lengths were multiplied by two, convert to FF (Full frame) effective. To avoid misunderstanding only FF effective focal lengths are described at the picture.
Since you need to position the lens on the different distance from the object for different focal lengthens, table below is describe it:
| Focal length, mm | 40 | 56 | 100 | 170 | 200 | 270 |
| The distance to the object, m | 0.2 | 0.3 | 0.8 | 1.4 | 1.6 | 2.2 |
The aperture for every lens was stopped down for two or three stops.
The result will be divided by three groups:
Focal length less than 60mm:
So, from the ear-nose-size point of view it is NOT recommended to take face portrait with the lens which focal length is less than 60mm (FF efficient).
For wide-angel lens you have to position the lens / camera close to the face. The nose will be much closer to the lens than the ears. As a result you will have perspective disproportion, a large nose and almost no ears.
However, nothing prohibits to moving away for two - three meters and takes a picture. But then you will need to crop the image to have face portrait.
The next group - the lenses in the range of 100mm - 200mm Focal length.
It looks like the best option to take a face portrait. Since the relative distance to the nose and ears is about the same – whole head “details” will look proportionately. Also there is no need for post-cropping.
Group three: 270mm Focal length
Basically, not too bad, but the picture looks somewhat flat.
To be clear, additional parameter - the distance from the face to the lens - should be taken into account. As it was seen from the distances table, when you take a picture by lenses with a focal length less than 100mm, you may poke someone's face. Be sure – nobody will like it. Lenses with a focal length of 170mm and above will allow you to make a shot from much more comfortable distance.
Conclusion: The best choice for face portrait - a lens with a focal length in 170-200mm range (FF efficient).
And finally - if you want to try something extremely different - try to take the portrait with the fish-eye lens…
Lenses used for picture examples:
Panasonic Lumix G 20mm f1.7 ASPH
Olympus Zuiko 40-150mm f4.0-5.6