# Shooting portraits of strangers

This was quite a discovery: Danny Santos has been shooting portraits of complete strangers on Orchard Road, Singapore. The story was featured on JPG Magazine with some beautiful examples and that post pointed to his Facebook album, which pointed to his blog post about it. This phrase he wrote made me think: “Suddenly, strangers were no longer unwitting victims subjects, they were now willing participants … and that gave different life to the photograph, and a new awareness and dimension to my idea of shooting in the streets.” Touches a weak point of mine: asking strangers for permission to photograph them.

What I like a lot about the photographs is their shallow depth-of-field. He talks about his material: a Nikon D300 with a 85mm f/1.4 lens. That’s a \$999 lens, so one can expect some good results.

Let’s see what that looks like in my depth-of-field calculator: there is one picture on his blog that shows him taking a picture of someone at +- 2m away, so let’s use that as distance. If we fill in the right values (1.5 crop factor for a Nikon D300, f/1.4 aperture, 85mm focal length, 2m distance, 3:2 aspect ratio) we get this:

Depth of field calculation
0.019 mm Circle of confusion
1.99 m Near limit (anything closer will be too blurred)
2.01 m Far limit (anything further will be too blurred)
2.8 cm Total (1.4% of the subject distance)

# Focal length for the common man: “portrait distance”

I remember that before I started photography on a serious level, I had some understanding of shutter speed, but none of aperture and focal length. Even when I read what they meant, I still couldn’t ‘picture’ it, had no feeling for the numbers. Let’s leave ‘aperture’ for another time and just concentrate for now on the concept of “focal length”

First of all, the focal length of a lens is not the same as the actual physical length of the lens. Yes, 200mm and 300mm lenses (telephoto lenses) tend to be longer, but they’re not exactly 200mm and 300mm long. For instance, the Sigma 55-200mm F4-5.6 DC HSM is 85mm (3.3″) long,  while the 70-200mm F2.8 II EX DG lens is 184mm (7.2″). Same maximal focal length, but more than twice as long.

So what is focal length? I could explain that it is “the distance from the center of the lens to the principal foci (or focal points) of the lens“, but that wouldn’t make it more comprehensible, would it? Well, I read through the theory, with tangens of the viewing angle and stuff, and I think I understand it (I’m an engineer, I actually like trigoniometry). A 200mm lens gives a viewing angle of 12° on the diagonal. Still not clear? That’s when I thought: let’s invent something more tangible: the “portrait distance“. Say you need a surface of about 72cm x 48cm (28″ x 18″) to make a portrait of a person (not just a headshot, but with some torso on it too). See some examples below:

Well, the distance between the camera and the person you’re making the portrait of, will be +- 20 times the focal length.