Lighting 102: Unit 2.1 - Apparent Light Size

Summary: Light size is not what matters in determining softness. Apparent light size is what matters.
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Would you use a bare speedlight to illuminate a shiny, metal car? That's what I did in this photo.

To be fair, it is a Hot Wheels car. I have a six-year-old boy, which means we have about 3 billion Hot Wheels cars in the house. You work with what you got.

(Hey, we can't all have access to a classic car museum.)

But a bare speedlight? Even with a piece of paper taped to it -- the same size as the fresnel head of the flash -- to knock down the intensity, isn't that a pretty hard light source?

Depends on who you ask. I think of it is a hard source. You probably do, too. But the car sees it as a huge softbox when the flash is about an inch above the car's roof. And what the car sees is all that really matters.


Take a look at the setup photo for the shot. One small speedlight head lighting the car. Another on the wall (with a blue gel) to create the background.

I made this photo to prove a point. A tiny light source can look big and soft. Conversely, a huge light source can look tiny and harsh.

Take the noon sun on a cloudless day, for instance. It is a huge sphere of light -- far bigger than our own planet. But it is 93,000,000 miles away. So it looks tiny. And harsh.

(But, from control number one, distance, we know that it has the ability to light large objects evenly...)

Back to light softness.

We tend to equate umbrellas with soft light and bare flashes with hard light. But that is not necessarily the case. It is all about how a light looks to the subject, not the light's actual size.

Why is this?


To explain, let's make the subject you. Here is a 43" Westcott Doublefold umbrella, from about 10 feet away. Not bad. Looks like a reasonably pleasing light source.


Now, here is the same umbrella from about 5 feet away. Looks bigger, right? Softer.

What makes a bigger looking light softer? To understand that you have to learn to think about your subject in terms of four different lighting zones. And we will be talking about three of them today.

The first is what you normally think of as the lit area. This is the area of your subject that receives the light and scatters -- or diffuses -- the light back at the camera. The term for this area is the "diffused highlight."

The unlit area has a very technical name that I hope all of you will be able to understand: We call it the... shadow area.

But what about the boundary between the two? That is called the "diffused highlight-to-shadow transfer area." Big term, but it should make sense. That border zone, more than any other area, is what defines a subject as being lit by hard or soft light.

Think of yourself as the subject again. The lit portion of you can "see" all of the light source. The shadow portion cannot see any of it. The border zone - the diffused highlight-to-shadow transfer area -- can see part of it.

Like this:


That is why larger-looking sources make for broad, smooth transfer zones. They disappear more slowly as you wrap your way around the subject away from the light source.

Hard sources are more of a "now-you-see-them, now-you-don't" kind of thing as you rotate away from them. Thus, very abrupt transfer zones.

Now think for a second about the differences between a silver umbrella and a shoot-through umbrella. You might think that the silver would always be more efficient. Not so.

Remembering our distance discussion, not only does our light get softer as we get closer, but it gets far more powerful. The actual light source of a shoot-through umbrella can be placed very close to your subject, making a huge, soft, powerful light source.

Not so with a reflector umbrella. Unless you want to skewer your subject's well-lit eyeball on that shaft.

I used to shoot with mostly silver umbrellas, but I have come to think of the shoot-throughs as more versatile for the above reasons. Take a look at this shot (and the setup) of my daughter, for example. As you can see, I can bring that sucker right down close to her and make a beautiful light source.

But umbrellas are not the only way to make a hard light softer. You can use walls and ceilings for that, too.

Your flash most likely zooms its head to compensate for different lens focal lengths. But that can also be used to control the size of the light hitting a bounce wall or ceiling. Which will alter the softness of the light, all other things being equal.

Here is a flash, about five feet from a wall and set on 85mm beam spread:



Here is the same setup with the flash on 24mm:



And just for good measure, the same flash with a diffuser, which approximates a bare-bulb flash:



(It is hard to tell because of the decreased intensity, but the whole wall is being lit by the flash.)

You can see how easy it is to alter the softness of your light source by using either an umbrella or a bounce surface in this way.

By zooming a flash out to ultra-wide and bouncing it off of a wall, for instance, you can make a huge light source to get results like this wonderful portrait by reader San Ramon (oops) Jason Lee.

Why just bounce your flash off of a wall or ceiling, when you can put a little thought into it and get exactly the size and shape of light source that you want?

You can point a flash at a wall right behind you and get an almost softbox/ringlight look, for instance.

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Size and distance are relative. But remember that the size/intensity/fall-off thing is always in play, too. More complex, more control.

As for the size/distance thing, I tend to think of a light source as reasonably soft if it's size is at least half of the measurement of the light-to-subject distance. That is to say that a 3-foot umbrella will be reasonably soft at up to, say, 6 feet from the subject. But that is just a rule of thumb. Your opinion may differ.
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We have two more exercises and then we will do a series of full-blown assignments working with the material we have covered so far. Learning just these two controls -- position and apparent size -- offers a wealth of possibilities. And we are gonna play some before going on to the other controls.

For this week, the exercise is a simple one. You'll be varying the apparent light source size and seeing the effects on your subject.

Our subject will be a piece of fruit. Your choice, but just a single piece. Use just one light source to shoot it. You may wish to position the source in a way to also light the background to separate the shadow side of the fruit. But that's old hat to you now, right?

Soften the light source however you like -- bounce off of a wall, use an umbrella, shoot it through a piece of wax paper -- whatever. But the important thing is to do a series of photos with the light source differing in apparent size.

This will mean moving the light source in some cases. Or altering the flash beam spread and/or distance if you are reflecting off of a wall. (Be sure to adjust your aperture to compensate for any different distances.)

For this exercise, try to keep the direction of the light source reasonably consistent. The idea is to see the differences caused by apparent size changes, not angular ones. We already did that in exercise 1.1.

Please leave caption info on each photo that will help others to understand exactly what they are looking at. Especially changes made with respect to the light source.

When looking at others' photos, study the highlight-to-shadow transfer areas carefully. They will tell the tale of the light source.

Tag your pix with:

strobist
lighting102 (note no spaces)
softness

You can see all of the completed exercises here.

Questions? Answers? Incoherent rants? Stick 'em here.
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Related Links:

L101: Umbrellas
L101: Bouncing off of Walls and Ceilings
Westcott Convertible Doublefold Umbrellas

Next: 2.2 - Specular Highlight Control

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