Well,
at least how I choose a lens for street portraiture. So that
we are on the same page, I am talking about meeting strangers and
asking permission to make a portrait. This is not about candid street
photography. This involves walking around with the camera (and lens!)
on a wrist strap (as I do), or some kind of a shoulder strap. Clearly
a light rig is preferred, and I will photograph people from about 6
to 15 feet away. As I am trying to establish a relationship, I want
to stay fairly close – at least within easy earshot. :-)
I
have been following the 100 Strangers Flickr group for about two
years. The posted images usually have the camera type, and the text
often mentions the lens and metadata. I can say that all kinds of
gear can be used, and any number of lenses can get the job done.
Nevertheless, there are some common themes that emerge, and the
aesthetics of the images are often dictated by limitations of glass.
And being opinionated, after having photographed hundreds of
strangers, I have fairly firm ideas about what makes a good lens for
street portraiture. :-)
OK,
so the first question is whether to use a prime lens or telephoto.
This, for me, is easy: prime all the way. There are a few obvious
reasons, and one not so obvious.
1.
Prime lenses are smaller and lighter than telephotos with similar
maximum apertures. When walking around for any length of time, this
is significant. Also, the smaller lens is less likely to be
intimidating to a stranger.
2.
By and large, prime lenses are cheaper than telephotos. As I'll
mention below, a fairly wide aperture is useful, and telephotos that
open up to f2.8 become pricey.
3.
In the lower price range, prime lenses tend to be sharper at wide
apertures. In portraiture, overall sharpness is not always desirable, but sharp eye sharpness is hard to beat.
Now
for the not so obvious reason:
4.
With a prime lens, you never have to worry about what focal length to
use. The decision has already been made. This is not trivial. I
consider it important to have all camera-related decisions made
before encountering strangers to approach. Then the mind is focused
on the available light, background, and the personal interaction.
That's plenty! It is counterproductive to also have to consider focal
length, ISO, aperture, etc. These should be set in advance.
OK,
so a prime lens, but what focal length and maximum aperture? For
focal length, the camera (system) and sensor size become important.
It is easiest to relate sensor size to full frame cameras, even
though I have never owned one. :-) For head shots, or head and
shoulder (my favorite), 85mm is considered ideal for full frame
cameras. Much shorter than 85mm leads to unflattering distortion; the
nose and cheeks look large, and the ears small. Longer than 85mm
gives good results, but the photographer has to get progressively
farther from the subject. For full frame cameras like the Nikon D600,
or Canon 5D Mark III, 85mm is (arguably) ideal.
But
what about cameras with smaller sensors? DSLRs with APS-C size
sensors, have a crop factor of approximately 1.5:1 (Canon and Nikon
differ only slightly here). I used to use a Nikon D90 with this
sensor. A 50mm lens is equivalent to 75mm for full frame: pretty
close. I used 50mm and sometimes an 85mm. The 85mm is equivalent to
127mm in full frame. The results are nice, but I did have to stand
back a bit more than I like.
Now
I use an Olympus OM-D E-M5 (who dreamed up that name?) with a micro
4/3 sensor; the crop factor is 2:1. So the 45mm prime lens is
equivalent to 90mm full frame. Close enough. Other camera systems may
have different sensor sizes. Relating them back to full frame and
85mm equivalent will help choose the appropriate focal length.
So,
lastly, what about maximum aperture? A couple of factoids:
1.
A lens with a wide maximum aperture can always be stopped down to f8
or f11. A lens with a smaller maximum aperture cannot be further
'opened up'.
2.
As a general rule, the wider the maximum aperture, the larger and
more expensive it will be.
So
what is the best maximum aperture for portraiture? Ah, it depends on
the aesthetics that you are trying to achieve and your
skill/limitations in controlling the depth of field. The trick (for
me) was to get a shallow enough depth of field to render the
background out of focus, but not so shallow that one eye was soft. I
had purchased a 50mm f1.4 for my Nikon D90. But I found that under
about f2.4, I usually got one eye out of focus. At f1.4, I got poor
results, and that is with the APS-C sensor. So I probably would have
been just as well off with a 50mm f1.8, which is smaller and cheaper.
The
full frame sensor has a more shallow depth of field, and the subject
has to be PERFECTLY square to the camera to get two sharp eyes at a
wide aperture. My Olympus OM-D E-M5 has a smaller sensor, so the
depth of field is a bit larger, and I can shoot at f1.8. But the
greater depth of field limits how soft the background can be
rendered. You pays your money and takes your choice!
So,
in conclusion, my not-so-humble opinion is that a good lens for
street portraiture is a prime, 45 – 85mm depending on the camera
sensor size, and maximum f stop 1.4 to 1.8 depending on sensor size
and personal preference. Some cameras have sensor sizes different
than mentioned above. The Nikon1 system has a 2.7:1 crop factor. As
long as you do the arithmetic and relate it back to full frame, they
can be compared properly.
Now,
after all this, in the 100 Strangers Flickr group, some members use
an inexpensive kit zoom lens, f3.5 – 5.6. Some use point-n-shoot
pocket cameras, and a few even use phones. Anything can work, as long
as you don't mind giving up aesthetic control.
Bob
