need help with lighting groups

On 2008-08-27 19:25:11 -0700, picture taker said:

wedding groups shots in church after the ceremony i always have light
fall on the corners .

24-70 2.8l exposure 125/4.5 i hate bumbing up the iso but do but still
am not happy doing that .
im using a canond 5d with the quantum t5d-r on a custom bracket .
i shooot raw and have a little room to open them up more but was
thinking about adding another light to get even lighting .
do any of you guys/girls have any experience with this type of
lighting ?
do any of you bring along studio strobes and use them for these shots ?

The first thing you have to decide is do you really want the whole
group evenly lit, or do you want to emphasize the bride in the center
of the group? Assuming you want the whole group evenly lit, your light
source is either too close to your subject or it is too small. These
problems are both typical of mounting the flash on or near the camera.
Bumping up the ISO will not help. It will just over-expose the center.
Anti-vignetting software might help.

It is helpful to distinguish between the light source (reflector,
window, softbox, diffuser, bounced light off ceiling, the sky, etc.)
and power (your strobe, the sun, light bulb, etc.). The power
determines how bright the light is. Brightness falls off with distance
in the inverse square rule, while the area lighted by the source
increases by the inverse square rule. What this means is that doubling
the distance from your light to your subject cuts brightness to 1/4 of
what it was, but increases the area lighted by 4 times. If you think
about it that makes sense. You are just taking the same amount of light
but spreading it over a larger area, so it is not as bright at the
subject.

What all this means is that the closer the light source is to your
subject the smaller the area it will light. The smaller the light
source is the smaller the area it will light. Consequently, if you want
to light a large area, you need either a large light source (big
reflector, Scrim Jim, soft box) or you need to move your light source
farther away. Either way, you end up needing more power, perhaps more
power than a single strobe can provide.

Diffusers increase the effective size of the light source, but often
not by enough to get the corners you want. They have the drawback of
sending most of your light in some other direction than the subject.
Most diffusers send just as much light behind the photographer as in
front of him. This effectively halves (or worse) the power of your
strobe. You can also use two light sources , one to light each half of
the group (this is really just a method of doubling the size of your
light source), but that can get tricky trying to make sure that the
light does not overlap too much in the center (making it too bright) or
not at all (making the center too dark).

Using two light sources, such as a strobe and a reflector, or two
strobes, generally allows you to fill in shadows or selectively make
part of the subject brighter than the rest. You may also need more
light sources if some of your subject is further away from your main
light than other parts of the subject (a common problem even with small
groups or even compositions of only two people -- in general, you do
not want more than 1/4 stop difference between two parts of the subject
if you want them to appear evenly lighted; this is where your handheld
light meter comes in real handy). Or you can use two strobes to
increase the power to a single light source, such as a soft box. But it
will not fix your problem if you do not make the light source larger or
move it further away.

Let us say that your group is very large, about 40 feet across. If your
light source was located right at the group, you would need (at a
minimum) a 40 foot light source. That is not real practical, unless you
are outdoors and your light source is the sky. For large group shots,
this is my preferred solution -- shoot them outdoors where I have, for
practical purposes, an infinitely large light source. For large indoor
group shots, where you are often restricted on how far you can move the
light source away from the subject (walls and furniture do get in the
way, don't they), you are simply going to have to bring a bigger light
source, usually in the form of diffusers, screens, reflectors, or giant
soft boxes -- and enough power to run the light source, such as a
studio strobe. Fortunately, you do not have to move a light source very
far to greatly increase its effective size -- the inverse square rule.
Doubling the distance effectively quadruples the size of your light
source. Tripling the distance makes your light source nine times
bigger, etc. And if you are going to go to that much trouble, you might
as well bring a second light source to create catchlights in the eyes,
and a third light source for the background -- well, you get the idea.

Another thing to remember is that the further your light source is from
the subject, the softer your shadows are going to be. This is also true
of the size of the light source. The larger the light source, the
softer the shadows. Thus you get softer shadows on a cloudy day
(diffused, very large light source -- the whole sky) than you do on a
sunny day (pin-point light source -- the sun). This again argues for
large light sources placed at some distance from a group.

It really does not matter how you increase the size of your light
source or move it further away. Umbrellas, soft boxes, reflectors and
the like all give you a larger light source. They differ only on how
efficiently they use your power (umbrellas are less efficient than soft
boxes, for example). It only matters that you do it if you want the
whole group to be evenly lighted.

Now, if the whole group is already even lit without additional
lighting, then you can use 'available light' to light the group. The
problem with this is that churches and large buildings tend to be dark,
so you end up using strobes and reflectors and stuff simply to make the
picture *look* like you are not using any additional lighting at all.
The way we get around this is to make the available light our main
light source and only use the strobe to add catchlights and freeze the
subject. We do this by using rear curtain sync. Obviously, this is not
going to produce results as sharp as those used by brighter strobes,
but it often gives a more pleasing overall effect. Plus, it can often
be done without using additional strobes, reflectors, soft boxes, etc.
You probably would want to use at least a diffuser, however, just to
keep the strobe from lighting the center too much. Rear curtain sync
sometimes works well when you do not have all the lighting that you
need, but it is unreasonable to expect that it is any sort of
substitute for adequately lighting the subject in the first place.

One way of studying lighting in others' photos is to look closely at
the subjects' eyes. There is often a reflection of the lighting setup
there. That 'catchlight,' for example, is usually just the reflection
of a strobe. It is not natural at all, but people like it because they
think it makes them look more lifelike. In fact, if you think about it,
it makes them look like a taxidermist gave them glass eyes. Whatever.
One thing you quickly learn is that people really do not want to look
like themselves. They want to look 'better,' and 'better' is highly
subjective.

--
Waddling Eagle
World Famous Flight Instructor