Andrew D asks:
I’ve pondered about this for a while … which is the most appropriate focal
length lens to use for portraiture (head/shoulders) and which is the most
“flattering”? I realize that it would vary for different sensor formats. So
pick a format. Or is distance between subject and camera the major deciding
factor?
I've rambled on about this for years and for 35mm I have to say anything
above 100mm works nicely, or 150mm+ for 6x6 (I like this format best, I've
seen some 6' high prints of faces taken 8x10 - not my cup of tea) - and now
the justification in the less verbose form than I normally take:
for 35mm format 24x36mm sensor the focal length and angles of view are :
28mm = 75 degrees
50mm = 43 degrees
100mm = 25 degrees
250mm = 10 degrees
500 mm = 5 degrees
1000 mm = 2.5 degrees
and from http://en.wikipedia.org/wiki/Human_eye#Field_of_view
"The approximate field of view of an individual human eye is 95° away from
the nose, 75° downward, 60° toward the nose, and 60° upward, allowing humans
to have an almost 180-degree forward-facing horizontal field of
view.[citation needed] With eyeball rotation of about 90° (head rotation
excluded, peripheral vision included), horizontal field of view is as high
as 270°. About 12–15° temporal and 1.5° below the horizontal is the optic
nerve or blind spot which is roughly 7.5° high and 5.5° wide"
nope, tried hard - going verbose on you all sorry - the field of view may be
270 degrees ( a tad more than the 180 most books claim) but a lot of that is
used by the brain to detect movement rather than using it to focus - When
we concentrate on a thing we bring it into a position generally around 15
degrees - corresponding to the 150mm-ish lens - which is probably why photos
taken with this focal length looks intimate and 'natural' (more natural than
a 50mm unless you are oblivious of other people's personal space and stand
nosetip to nosetip with your victims, sharing breath and odors) If our
eyesight was better as mine once was, we'd probably be comfortable with even
longer focal lengths. I suspect those teenagers who walk either side of a
main road shouting at each other across everyone else's heads may prefer the
familiarity of a 250mm or possibly a 500mm but then they smear their noses
on their mobiles while hunched in dark corners too so there's no making
sense of this.
We also have the issue of saccades and microsaccades motion, wriggling our
eyeballs around like demented whirlygigs (whirlybugs?) - this stops our
chemical receptors from depleting.. where our eyes not to jiggle it can lead
to people shrieking 'I'm BLIND!.. no, wait.. no there we go, better now' -
actually this occurs with some drugs that still your eyes, the vision can
just fade away until you move your eyeballs. There are a few neat optical
illusions that can bring this on too.
I love vision, it's such a weird thing given our eyes are actually total
rubbish. Blindsight, psychosomatic blindness, and that horrible thing where
physically blind people SWEAR they can see and it was just the bird outside
the window distracting them that caused them to bump over the table (non
existent window, non existent bird) - in this sad case the brain is totally
using memory to fill in the gaps (hey, the brain wants to see, so it sees by
damn) and the person truly believes they can see.. even if the blindness
takes the form of missing eyes. poor things.. our brains can be so MEAN.
Jellyfish eyes are neat too, there's a nasty little thing the size of an
iceblock floating around the Northern Australian waters (they get washed
down to the Southern beaches with the North currents in winter too) -
transparent, known as stingers, box jellyfish, sea wasp or Irukandji
(actually putting 'lethal' in the search engines when typing in 'australian
animal' is often redundant) - the thing has 4 defocused light sensors which
barely qualify as eyes but researchers noted they were doing some weird
things when they dropped individual brine shrimp (sea monkeys) in to feed
these guys.. they actually turned and actively tracked and chased them
around the tank - bear in mind sea monkeys (not the castle building variety)
are about 1/1000 the size of these near-blind jellyfish - and also keep in
mind that jellyfish also do not have a central neural cluster.. yup, they're
brainless. Turns out the current theory is that neurons may have parallel
evolved and rather than taking the form of a 'brain' for central processing,
these little blighters actually decided (that's a biological pun) to evolve
a parallel process neural mesh - their who body is one multipurpose brain of
sorts!
I had red livid welts for a month every time I swam into an unseen one and
the scars took well over three months to go down. I bet each of them saw me
though..
That may sound weird, but then again octopus and squid chromatophores may
turn out to be dual function too serving as whole body light receptors, and
we already know they use a whole body neural mesh as an alternative brain -
as in the extreme example of the squid Octopoteuthis - which actively
removes it's own arms occasionally and leaves them to hunt while it's off
hiding somewhere safe - (they eat their own arms later along with whatever
the arms kill) .. those detached arms have been observed as acting as
though they almost see their prey.
then there's those little cowrie (cowry) shells popularized by their use as
currency in certain islander cultures - those guys are completely covered in
eyes! Don't get me started on mantid shrimps (#2) those guys are nuts!
(did I mention their optic nerve feeds in parallel? parallel ! to a brain
the size of a grain of sand !! )
I wonder what focal length they'd prefer.. they probably have preferences
as to the type of glass the lens is made from !
so many questions, so little time.
(# 2http://arthropoda.southernfriedscience.com/?p=2964 )
