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Monday, July 09, 2007

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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Brand new to Strobist, or lighting? Start here.
Or, jump right into our free Lighting 101 course.
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29 Comments:

Blogger Aaron said...

There's a little diagram that I'd created based on my own experiments on apparent source size. Some of the readers here might find it useful.

July 09, 2007 1:32 AM  
Anonymous David Duncan said...

After reading on here how to light cars at night, I shot these about three weeks ago. www.davidduncan.com/rover. These were shot outside at night, with the bugs and heat. This was a friends SUV.

As always, great site.

David Duncan

July 09, 2007 2:08 AM  
Blogger Brock said...

David, the first shot shown here of the car has decidedly more shadow area than shown in the set-up shot.

What did you do with the overhead light source to get those shadows that we don't see in the "set up" shot?

July 09, 2007 3:14 AM  
Blogger Jazzology said...

The car shot is an illustration of exactly how the full size version is shot. I have seen an entire studio turned into a softbox... usually the illumination is provided by flos or large pan lights to avoid hot spots in the diffusion. one thing I dont see a lot of mention of in "Strobist" is the use of "bounce"... in a small area it is a great way to increase the apparent point source size.

July 09, 2007 7:19 AM  
Blogger JanneM said...

"diffused highlight-to-shadow transfer area."

A good word for this is "penumbra". Shorter and easier to use than the whole thing above. Best of all, it means exactly what you describe, though usually used in astronomy.

July 09, 2007 8:28 AM  
Blogger David said...

Janne-

You are right about "penumbra," in the astonomical sense.

But the analogy does not really carry over to the concept of altering the relative densities of the diffused and specular highlights to control the tone of your subject, which we will be talking about next week.

July 09, 2007 8:40 AM  
Blogger David said...

Brock-

I was moving the light around a little during the shoot and I think I choose a shot where the light was at a harder angle (i.e., further back) in the lede photo edit as opposed to where the light was in the setup shot.

-D

July 09, 2007 8:48 AM  
Blogger Sean Phillips said...

Is it really a bare speedlight when it's covered by a piece of paper??

July 09, 2007 1:11 PM  
Blogger David said...

Sean-

Yep. The paper was there only as a "poor man's neutral density filter." It served only to knock down the light output of the flash, which was far too strong at even 1/64th power this close. I do that all of the time.

Mind you, the size of the light source was not changed (paper being the same size) which is what matters in this exercise.

If I had diffused the light through a piece of paper larger than the flash head, your point would have been well taken.

-DH

July 09, 2007 1:46 PM  
Blogger Zey said...

Before doing a routine reading on your blog, I was photographing my own car with 2 SpeedLites. Your site really helps me alot in lighting knowledge. Here is the result if you wish to check it out: http://www.pbase.com/zey/my_vios. Thanks alot and I'll try to use the flash barehead as softbox on tiny subjects.

July 09, 2007 2:13 PM  
Blogger Brock said...

That's what I figured, David, but I had to ask to make sure I wasn't missing something.

July 09, 2007 3:14 PM  
Anonymous Tim Solley said...

As always, great content David. I used to shun my transparent umbrellas until I realized I could get them right there in the face of little kids I was shooting without a) skewering them with the rod and b) taking the time to put together a softbox. Now the only problem is that little babies love to play with the knob in the center of the umbrella!

July 09, 2007 3:32 PM  
Blogger Jerome said...

very cool. you're a very gifted teacher david. we truly appreciate all of this. just looking at the already posted examples, have also taught me alot. ill try my best to experiment but im out of state right now and don't have a home pc that is suited for transfering photos.

July 09, 2007 9:12 PM  
Anonymous ruthdeb said...

Y'all should check out Aaron's diagram of what causes those diffusedHighlightToShadowTransferZones to act the way they do. Picture worth 1000 words.

July 10, 2007 10:31 PM  
Anonymous Anonymous said...

FYI, I recognized the baby portrait and I think the photographer of the baby portrait is named Jason Lee, not San Ramon. I think he might be from San Ramon, but if you carefully look at his Flickr profile, it has his name as Jason Lee (it is a little confusing, I would have thought he was saying his name was San Ramon, too).

July 11, 2007 9:06 AM  
Anonymous Anonymous said...

You wrote, "If I had diffused the light through a piece of paper larger than the flash head, your point would have been well taken."

I thought that tracing paper over the flash head would act as a diffuser. How is using something like that unlike (for example) putting the plastic diffuser into the head on my Vivitar 285HV?

Thanks.

July 14, 2007 8:40 PM  
Anonymous Anonymous said...

I saw this real size huge source of light for a Bugatti shooting session: http://www.youtube.com/watch?v=NqpEzsjeIT4

July 16, 2007 11:49 AM  
Blogger Photography Luna said...

The issue about the piece of paper being a diffuser or just a neutral density grad filter is not in the size/material being used I think, but in the distance between the lightsource (being, the speedlight) and the piece of paper. Since it actually is 'on' the speedlight, it is a grad filter, whereas it would be a diffuser if it was a few inches away from the speedlight.

http://photographyluna.blogspot.com

July 30, 2007 2:36 AM  
Anonymous Ger said...

You Rock...A gifted teacher.. I have learned so much from these few lessons than reading a lot books and doing courses...I'll be on tender hooks for the next lesson once I catch up. You're an excellent teacher..removing the rubbish and giving the facts in simple english will well backed up examples...There will be a seat beside God for you in heaven..

Ger..

August 31, 2007 10:48 AM  
Anonymous Lomoseb said...

Yes again ! David rocks ! Thanks a lot.
Don't know where to put this but i will interest a lot of us and certainly you david (if you don't already know him) :
Denis Rouvre
These man's lights rocks too.

September 10, 2007 5:36 PM  
Anonymous mattcvs said...

didn't know if this was mentioned before... but i had an idea to use as a reflector... i bought a car window sun shield thing a while back, and just recently it occurred to me it's shaped very much like a "professional" light reflector... but definintely did not cost upwards of $40. granted, it's not the most perfect reflector... but it worked well enough when i tried it out.

posted a few pics on my flickr page... i'd suggest experimenting more with distances before recommending it... but most people already have one of these around the house (or garage), and it seems to work well for close ups...

December 08, 2007 4:29 PM  
Anonymous mark said...

so YOU took that photo that's on your wall! wow... I've seen that a few different places. :)

thanks for all the great ideas!

-mark

December 27, 2007 11:44 PM  
Blogger Matjaz said...

Apparent light size. Wouldn't it be sooo geeky to invent/propose an l-number?

Much in the same way as the f-number is the focal length f divided by the entry pupil diameter d, the l-number (l for light, see) would be the distance l to the light source, divided by its size d.

So, an 18" softbox hung 18" away from a model's face would make an l/1 lit portrait.

Sun looks like 30 arc minutes across from where most strobists live, making sunlight a harsh l/110. So does my bare strobe at 5m distance.

The analogy goes on a bit. The f-number works its way into out-of-focal-plane "softness", the l-number does it for penumbra.

April 22, 2008 1:40 PM  
Blogger storbist_wanna_be said...

Mr Hobby,
Thanks for your wonderful site, you just make my day, i was able to achieve the lighting effects that i wanted through manual off camera flash, i was able to balance the ambient and flash on my preference. more power to you sir!

November 23, 2008 5:40 AM  
Blogger Spencer said...

Outstanding. I'm enrolled. And loving it. Thanks...

October 14, 2009 10:26 PM  
Blogger Guillaume MENANT said...

I'm currently following your L102 lessons and exercices and posting articles on my website to share my foundings : www.guillaumemenant.fr Thanks for these articles David !

November 04, 2010 3:54 AM  
Blogger Sarah said...

Hi, I have just started to follow this blog and am finding it very interesting in getting to know my SB-900 and finally get some use out of it. I am trying to replicate the photos here to see the different spreads at various zoom settings but when I take a photo the whole wall is lit at 18mm and the same at, say 105mm. I can't get that tight beam that you did. Is there something I am missing? Thank you.

August 21, 2011 5:42 AM  
Blogger WallArt said...

Depending on your imediate surroudings,the behaviour of the light to shadow transfer zone seems directly opposite to what it should be. In reality...this excersise is impossible unless you live in a black felt room or are shooting in low light outside where there are no reflective surfaces (assuming you varied the apparent size of the source by moving it further away). I know some people will already know this but i'll explain anyway. When you move the light source farther away, you should see the transfer zone width reduce and the shadow getting darker quicker, due to the fact that the subject can see less of the reduced light size. But you also have to take account for the inverse square law in this situation. If the subject to background distance stays the same, then the further away you move the source (and increase brightness to compensate), the more you increase its depth of light. This means that the difference in brightness between the subject and the background ( AND ALSO THE REFLECTED LIGHT HITTING THE SUBECT FROM THE BACKGROUND) becomes less. Therefore the amount of reflected light hitting yoyr subject from behind is actualy getting closer to the amount of light hitting it from the front. Hence........shadows VANISH. Conversely, moving the light closer increases its apparent size and therefore should make the light wrap around the subject more, giving a more gradual light to shadow trasition zone, and even lighter shadows. BUT...having the light so close to the subject and background means that (due to the inverse square law), the falloff of the reflected light is increased, resulting in less reflected light hitting the rear of the subject, Hence the shadow is REDUCED....contrary to what we expect to see. Confused ?

August 30, 2012 9:26 AM  
Blogger John Kimbler said...

Just wanted to stop by and tell you how much this post helped me to setup my lighting for macro photography, and I point other macro shooters to it every chance I get :)

Regards,
John (aka Dalantech)
My gallery

August 01, 2014 3:51 PM  

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