Saturday, November 9, 2013

2 - Apparent Light Size

In last week’s post I discussed my progress through the L102 lesson on position.  This is the first of seven ways to control light.  The takeaways from this lesson were:
  1. By altering the angle of our light source we can control how highlights/shadows are cast upon a subject.
  2. By altering the distance ratio between our subject and the flash versus the background and the flash we can control the exposure of the subject and the background independently.
This week I’ll be discussing’s second way to control light apparent light size.  This lesson begins with an exercise that illustrates the effects of altering the apparent size of a light source and then gets into a discussion on Specular Highlight Control.  Hopefully by the end of this post that last term won’t sound so foreign and complicated.

The first exercise instructs readers to take a series of photographs while changing the apparent size of a light source.  Please note that there is a major difference between simply the size of the light source and the apparent (or relative) size of the source.  When thinking about the apparent size you need to think about the size of the light source from the subject’s point of view.  Ask yourself how the subject sees your light source. 

For instance, a speedlite might look huge to a matchbox car, if it’s close enough, but tiny to a full-size sedan.   To get the same effect on a full-size sedan as the matchbox car, you just need to use a light source that is slightly larger than the car.  Sounds easy, right?  In my Headshots post I discussed bouncing a flash off a wall or ceiling.  Instead of using a car sized flash you could use a room sized ceiling to bounce a small flash off of.  By bouncing the flash off a ceiling the car would see the entire ceiling as the light source.  Other ways to modify the size of a light source include umbrellas, softboxes, reflectors or any number of things.  When using these, the subject is no longer seeing the relatively small speedlite as the light source but the entire modifier as the light source. 

Using a bare speedlite
Using a shoot-through umbrella
To the right are two photos using a pumpkin as the subject.  In these photos the distance of the light source was constant.  I shot with a bare flash in the first shot and then modified the flash with a shoot-through umbrella in the second.  Notice any difference?  

The bare flash in the first shot was an apparently small light source that creates a harsh shadow.  This is referred to as hard light.  The umbrella used in the second shot diffused the light over its entire surface making the area between highlight and shadow much larger.  This, photographers refer to as soft light.   It’s important to remember that whether a light is hard or soft has nothing to do with how powerful the light is but rather the apparent size of the light source.

The apparent size of a light source also depends largely on distance.  In the last example I kept the distance between the pumpkin and the flash constant.  Now try to visualize what would happen if I used that same shoot-through umbrella but instead of being two feet away from the pumpkin the umbrella was, say fifteen feet away.  Would the umbrella still be an apparently large light source? 

To help answer this question, think of the largest light source you can think of, the sun for instance.  We know from elementary school that the sun is incredibly large (and powerful), but on a clear sunny day it casts harsh shadows.  How can this possibly be!?  It’s because the sun is also incredibly far away.  This principal is the same for your speedlite, the farther away it is the smaller it is, and the more powerful it needs to be.  Now on a cloudy day you get much better shadows.  This is because the clouds are diffusing the sunlight making the entire sky your light source.  You can think of a cloudy sky as giant shoot-through umbrella.  This diffused sunlight also improves color saturation.  So go out and have fun when the sun is shining, but when the clouds roll in, go grab your camera.

Up close the umbrella makes a huge impact compared to the bare flash.  When that umbrella is moved out to a much greater distance the umbrella doesn’t make the light source apparently much larger.  It’s really just robbing power out of your flash so at a large distance you might think of ditching the umbrella.

As part of this exercise, instructed us to use a fruit, of our choosing, to be the subject of this exercise.  I typically work through these exercises a week or two before my post discussing them is published.   This means that even though this post is published in November, I was working through the exercises in late October so I felt using a pumpkin was fitting.  I realize I failed to follow one of the easiest instructions of the exercise by choosing a pumpkin as my subject but it just seemed right at the time.  I also learned this week that a pumpkin, believe it or not, is a fruit.  Now I feel like I’m just making shit stuff up.  I also no longer think I have a clue as to what a vegetable is.

Most speedlites also have a zoom function, so I wanted to debunk a misconception that you might have on how this effects the apparent size of the speedlite.  Let me show you an example of how this works.

Flash at 24mm zoom
Flash at 105mm zoom - no change to apparent size
The zoom function on your flash focuses the flash to light only what it needs to.  At a small focal length you need to spread that light out to cover your entire frame, if that’s what you’re looking for.  At a larger focal length you only need to light the smaller area that is inside your frame.  This allows you to waste less light outside your frame.  The zoom function on your speedlite might be expressed in mm.  This roughly corresponds to your lens’ focal length, if that flash was mounted on your camera, to illuminate the entire frame.  In this first photo my speedlite is zoomed all the way out to 24mm.  In the second photo I zoomed the flash all the way in to 105mm.  Notice any difference in the highlight or the shadow?  

There isn’t much because the zoom function of the flash does nothing to the apparent size of the flash.   At 105mm I’m wasting much less light outside the frame so I need less lighting power but the size of the light source remains constant.  You can see that the second photo is slightly brighter over all because of this.  Please ask questions in the comments section below if this explanation has left you confused. 

Now let's get into Specular Highlight Control.  This is a pretty scary term, at least it was to me, but hopefully it won’t be once we are done.  A specular highlight is the light reflecting directly off an object into your camera. Look again at the last shot of the pumpkin.  That reflection of the light off the left side of the pumpkin is the specular highlight.  You can control the specular highlight by the position of the light source and/or by modifying the shape and size of the light source by using an umbrella, softbox, etc.  To illustrate this control I used a billiard ball.  It is highly reflective so it is easy to see changes to the specular highlight. 

Bare speedlite
In the first shot I used a bare flash and you can see that small light source reflecting off the ball.  I modified the light source in the second shot by using a shoot-through umbrella.  You can clearly see the reflection of the umbrella on the billiard ball.  These are specular highlights.  These highlights can be modified by modifying a light source.

Shoot-through umbrella
You can also notice a second reflection on the top of the ball in both of these shots.  This specular highlight is caused by a second flash bouncing off of the ceiling.  You can add as many specular highlights as you wish. You are only limited by how many light sources you have available.  You can also click on these photos to see them full size.  If you do, you can also see a third specular highlight on the back left side.  This one is caused by a tungsten lamp behind and to the left of the ball.

That’s it, that’s the specular highlight and a couple ways to modify it.  It’s not so scary now, is it?  

To play around with this more I took a third shot of the billiard ball.

Can you tell what the light source is, how many there are, and what I’m using to modify them?  Instead of just telling you the answers straight away I’d like you to take another look at the photo and let me know what you think the answers are in the comments section below.  Reverse engineering how other photographer’s photos were made will help you when you’re planning your own shoots.  I’ll let you know in my next post how this shot was created.

There are two upcoming assignments in the L102 coursework.  The Position and Apparent Light Size lessons include exercises that illustrate these controls.  The exercises are not designed to create great photos to hang on a wall. They are designed to allow you to play around and learn the controls in a practical way.  Assignments are focused on refining your skills to produce a finished product.   In my next post I’ll be discussing my progress through the Cooking Light and Umbrella Specular assignments.  You can preview these assignments on, here, for a sneak peek at the goals of these assignments.

Until then, try these exercises out for yourself and continue having fun with your camera.  I’m always excited when I finish a blog post because it means that I can go shooting again!  Don’t forget to add any questions you have in the comments section and let me know how you think I created the last photo of the billiard ball.

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