For today's post we will cover a topic that isn't
discussed a lot, but is fundamental to lighting. The term “family
of angles” doesn't come up often, if at all in most circles. Is it
useful for you? Read on to find out...
Terms
Defined
Before going any farther, I want to define some of the
terms that are related to this discussion, just to ensure everyone
gets this bit of background. These are my definitions, feel free to
consult the Wikipedia or your favorite source for better terms.
Direct Reflection Reflections that mirror the light
source, as one typically gets from a hard, smooth surface, such as
glass, plexiglass, metal, plastic, etc., materials that are shiny.
Direct reflection does not diffuse the light in any significant
manner.
Diffuse Reflection Reflection that gets diffused, that
is, scattered all directions rather than simply mirroring the source.
Diffuse reflection is typically associated with textured surfaces
like cloth, skin, dirt, uncoated paper, etc., materials that are not
shiny.
Angle of View Abbreviated as AOV.
The angle extending out from a lens along the path of what the camera
can see. It is worth noting that while focal length affects the field
of view, the sensor size also affects Angle of view. For example, a
100mm lens with a 35mm sensor will yield a wider AOV than the same
lens with a 23mm (APS) sized sensor. See the image below for a
graphical depiction of this.
Field of View Abbreviated as FOV.
The rectangular area describing what the camera can see at a
particular focus point. This is similar to AOV except it describes
the rectangular area at the focal point, so the FOV
increases/decreases correspondingly with an increase/decrease of the
focal point. Because FOV is associated with AOV, it too is affected
by sensor size
The
Basic Premise
The term “family of angles” refers to the angles
from which if light is sourced, a reflective surface will direct
light back into the lens creating visible light spots. For a flat
surface, the family of angles are the same as the lens' angle of
view, but coming back toward the camera. Throughout this discussion
it is assumed that the surface being photographed is flat and
reflective, which could be glass, plexiglass, metal, plastic, etc.
In the above diagram the dotted line represents the
family of angles and is equal to the angle from the lens' field of
view. When light is sourced anywhere within this family of angles, it
will reflect off of the surface being photographed and back into the
lens.
From this diagram you can see that using a longer focal
length from a greater distance will reduce the family of angles. Now
that the lights are outside the family of angles light will not
reflect back into the lens, thus eliminating direct reflections.
What's
The Point?
The point is, knowing about the family of angles takes
some of the guess work out of lighting. It is actually an intuitive
kind of thing, but giving it a name makes it easier to discuss and
for me, modeling it on paper drives it deeper into the gray matter.
Knowing about the family of angles helps me to control
reflections.
I can add them when they're wanted...
...and eliminate them
when they're not.
When shooting materials that are somewhat
reflective, and especially for those that are highly reflective, if
I'm getting unwanted reflections, I know to either move the lights
outside the family of angles or use a longer focal length and move
the camera back. There are times I may want reflections, like filling
a pair of sun glasses or the entire side of a metal object. To do
this, I know to place a light source inside the family of angles.
By now someone has no doubt noted that not all objects
are faced perpendicular to the camera and not all objects are flat.
When the subject is turned, then the family of angles move
accordingly along with the subject. This concept can also be applied
for non-flat surfaces; you need to adjust for whatever curvature you
encounter. A concave surface will reduce the family of angles whereas
a convex surface will increase the family of angles. If photographing
a sphere you are out of luck, as all angles reflect back into the
lens, so the family of angles are 180º. There are ways of dealing
with it, but that discussion is beyond the scope of this little post.
Read
This!Publish Post
I have only scratched the surface for how the family of angles plays into photographing various materials. If you care about lighting, please do yourself a favor and get a copy of the book “Light: Science and Magic: An Introduction to Photographic Lighting” by Fil Hunter and Paul Fuqua. It covers this subject and much more, in-depth and in a way that makes it interesting and easy. Google books has an excerpt here.
I have only scratched the surface for how the family of angles plays into photographing various materials. If you care about lighting, please do yourself a favor and get a copy of the book “Light: Science and Magic: An Introduction to Photographic Lighting” by Fil Hunter and Paul Fuqua. It covers this subject and much more, in-depth and in a way that makes it interesting and easy. Google books has an excerpt here.
Coming Next
The next post covers a little product photography from a recent shoot. Come on back and I'll show how I approached lighting a larger than tabletop object.
The next post covers a little product photography from a recent shoot. Come on back and I'll show how I approached lighting a larger than tabletop object.
Until then...
-Gene
