The Ultimate Diffusion & Bounce Test

Introduction

There is a huge chasm between knowing lighting tools and knowing them intimately. Regardless of the approach, it takes a long time and a lot of experience to get to the latter. There is a wide array of options on the market, so how do you know what to use and when? I have been shooting for some time now, and assisting those better than me for even longer. I have had the opportunity to work with a wide array of lights and lighting augmentation, but its only been a few items at a time, sometimes spread over many months (or years) before seeing them again. Many cinematographers have their go-to approach to bouncing and diffusing light by always keeping a small selection of materials in their kit. Oftentimes, these were chosen because of what’s available. Other times, we hear its good, so we use it. But unless you’ve had a lot of practice and seen the side-by-side effects of each, it can be hard to know what would work best in a given situation. Because of this, I decided to conduct an in-depth test of various diffusion and bounce materials centralized in one location in a controlled environment. Welcome to the Ultimate Diffusion and Bounce Test.


A little background. I am a documentary cinematographer who has to shoot a lot of interviews for my projects. Interview lighting can range from a simple, no-frills, one-light setup to a massive lighting package with hours of setup time. Regardless of the scale, you want the interview to look as good as it can. Just shining a light on someone doesn’t always produce the most flattering look. You generally need to soften the light by either diffusing it, bouncing it, or both. The decision of which to do, and what materials to use is the question. What look are you going for? Is you space limited? How much time do you have to set up? What’s your budget? All of these factors play into the decision – and having an answer to these questions is an important first step.


This test is designed to answer some of those questions. I must admit, this is primarily a selfish test to see what I like best. But it is also a test to give all cinematographers a resource to look at the same materials and decide for themselves what looks best to fits their needs. This test is by no means limited to documentary interview lighting. These tools are the same used for any lighting setup, whether you’re shooting a documentary, commercial, or feature film. Every material, whether diffusing or bouncing, augments the quality and output of the light source to produce a specific look and feel.



Test Sections

I have broken down the test into three sections: Diffusion Only, Bounce Only, and Bounce with added Diffusion. There are a wide array of materials on the market to fit these needs, but I have narrowed them down to the most widely used and available options.

Diffusion:

Bounce:

  • Full Silk

  • White Griffolyn

  • 1/4 Stop Silk

  • Ultra Bounce

  • China Silk

  • Bleached Muslin

  • Full Grid Cloth

  • Unbleached Muslin

  • 1/2 (Lite) Grid Cloth

  • Bead Board

  • 1/4 Grid Cloth

  • Frost

  • Opal (Lee 410)

  • 1/2 White Diffusion (Lee 250)

  • Full White Diffusion (Lee 216)

  • Bleached Muslin (also tested as a bounce)

  • Unbleached Muslin (also tested as a bounce)


Methodology

Bear with me, this test is exhaustive. I tried to include as much information as possible to give you a well-rounded and in-depth look at the materials. There is a lot in here, but I tried to break it down in as digestible of a manner as possible. Take what you need and the leave the rest for later.


To conduct a test like this, you first need to establish a set of guidelines that will allow for a consistent and equal comparison of materials. There are a few sets of criteria to consider: Consistency in the lighting instrument, the size of the light source, the distance of the source to the subject, and light pollution.


Lighting Instrument

For this test, I have chosen to use a K5600 Joker 400. Since we are shooting in a studio with no windows, the Joker 400 will give me an optimal exposure range to test with without having to slow down the light with scrims or ND filters in front of the lens.


In the most extreme case, the Joker 400 flooded outputs 500 foot candles at a distance of 6′ from the subject. This is equivalent to an f/18 at ISO 800.


As we add diffusion, bounce the light, or add diffusion to the bounce, there will be an adequate exposure that ranges between f/2.8 and f/18.



Size of the Source

In each of these test setups, the effective “light source” will vary. Sometimes it will be the Joker 400 when nothing is in front of it. Sometimes it will be the diffusion in front of the light, and sometimes it will be the diffusion in front of the bounce. See where I’m going with this? Ultimately, whatever is the “last line of defense” from the light to the subject is the “light source.”









The larger the diffusion or bounce material is, the more it spreads the light. Because of this, I tried to keep the size of the various diffusion and bounce materials consistent, since the size of the “source” will have an effect on the spread, or softness, of the light. Nearly all of the materials are the same size, but there are a few outliers, due to physical restraints.


All of the diffusion materials are 6’x6′, with the exception of the gels – Opal, 1/2 White Diffusion and Full White Diffusion. This is because it comes on a roll limited to 4′ in width, so I unrolled it to 4’x4′. All of the bounce materials are 6’x6′ with the exception of the bead board. Again, this is limited to a maximum of 4’x8′, so I again went with 4’x4′ to keep the shape consistent.



Distance of the Source to the Subject

Since I am selfishly doing this test to compare looks for an interview setup, I went with a distance that is most tailored to that for the size of the studio, the size of the diffusion / bounce, and the intensity of the light. But there is something very important to keep in mind with this – The Inverse Square Law.


This law essentially states that if you double the distance between your light and your subject, you will reduce it’s intensity by 75%. Instead of being a constant reduction in light over distance, it is in fact and exponential change. What this effectively means is the light falloff is more dramatic the closer the light is to the subject. For example; If you setup a light close to two people standing in front of each other, the exposure on the person closer to the light will be significantly brighter than the person standing further away. But if you move the light further away, then the exposure difference from person to person will be reduced. The Inverse Square Law only holds true with a point of light, so the properties change as you bounce or diffuse light, but this is still very important to keep in mind when placing all of the instruments. We must keep a consistent set of distances between the light, the bounce, the diffusion and the subject so our values remain as constant as possible from test to test.



You can see with the image to the left, at 6′, our subject is much brighter than the background. The falloff ratio closer to the light is far more pronounced. As the light moves further away to 10′, our subject and the background become more balanced in exposure because of the exponential change in light value. Ss the distance from the light to the subject becomes greater, the falloff becomes less dramatic.


In our setup, the “light source” is always 6′ from the subject and the light itself is 4′ from the “source.” So in the Diffusion Only scenario, diffusion is 6′ from the subject and the Joker 400 is 4′ behind the diffusion. In the Bounce Only setup, the bounce is 6′ from the subject and the Joker 400 is 4′ in front of the bounce. Lastly, in the Bounce with added Diffusion scenario, the diffusion and the Joker 400 are 6′ from the subject and the bounce is 4′ from the light/diffusion.


As we break down each testing section, you can see the lighting diagram illustrating these distances.



Light Pollution

This is the tricky part. It is challenging to do a scientific study on the particular aesthetic qualities of these materials, since some are designed to maximize the spread of the light, while others are designed to soften, yet restrict the spread. Light, in it’s nature, bounces around off any and all surfaces it comes in contact with. So if the diffusion material is designed to spread the light, then there is more light to interact with the environment than a diffusion designed to limit the spread.


For the setup, we are working in a studio with the windows blacked out. There is no other source of light than the one we are testing. We have also not added any fill or negative fill that otherwise isn’t in the space, such as the floor, walls and ceiling. If we were working in a black box theater, the encompassing darkness would have an impact on the lighting by adding negative fill. Conversely, if we were working in a solid white studio, there would be a lot of natural fill from all directions. Our studio has a 12′ high white ceiling, wood floor, and a 25′ wide room with a brick wall and blackout material on the key side and partial white wall on the fill side. There is no one consistent tone in the room to overly influence the lighting one way or another. The only “flagging” of light we did was with barn doors to limit the spill of the Joker 400 to only hit the bounce or diffusion and not inadvertently spilling out to the wall or ceiling.


Setup 5′ behind our subject is a grey seamless paper. This midtone color will help illustrate the light falloff, spread and intensity of the various materials without affecting the overall lighting of the subject. You can see this clearly as the grey card in the wide shot either blends in with the backdrop or is significantly brighter than the backdrop.









Metering


While just looking at the image produced with each material is incredibly helpful in deciding which to use, we also want to know what’s happening with the light. To do this, we will take two meter readings.


The first is with a color meter. In this test, we are working with a Minolta Color Meter IIIF. We will take a color reading of the Joker 400 by itself to determine a base color temperature, and then meter the light with the diffusion or bounce added. This will allow us to see if there’s any shift in color with the given material.


The second is with an incident light meter, in this case the Sekonic L-758 Cine meter. We will again take a base measurement of the intensity of the Joker 400 on its own from various positions, depending on the material being tested. We will then take a measurement with the diffusion or bounce added. This will allow us to see how much light is eaten up by the material.






These incident readings will be measured in footcandles (F.C.) so we know an intensity value regardless of the ISO or f-stop of the lens. To convert F.C. to a ratio understood by your camera, just remember this formula:



When shooting 24fps at 180° (1/48th sec) shutter – ISO 100 with 100 F.C. you will have an aperture of f/2.8.

You can then adjust as needed to reach your desired ISO or f-stop.


Since light is doubled or halved as you double/half the ISO or open or close one f-stop, this is an easy adjustment to make. If you double the ISO to 200, then you halve the F.C. (to 50) to achieve an f/2.8. If you stop down the lens one stop to f/4, then you would double the F.C. to 100. Make sense? Here is a chart to make it even easier.

f/1.4

f/2

f/2.8

f/4

f/5.6

f/8

f/11

f/16

ISO 25

100

200

400

800

1600

3200

6400

12800

ISO 50

50

100

200

400

800

1600

3200

6400

ISO 100

25

50

100

200

400

800

1600

3200

ISO 200

13

25

50

100

200

400

800

1600

ISO 400

6

13

25

50

100

200

400

800

ISO 800

3

6

13

25

50

100

200

400

ISO 1600

2

3

6

13

25

50

100

200

ISO 3200

1

2

3

6

13

25

50

100

ISO 6400

.5

1

2

3

6

13

25

50

*24fps @ 180° Shutter

Working this way is great if you are on a location scout and don’t bring along a camera, or need to communicate light values without having to explain to your gaffer what ISO or f-stop will be on your camera. You can decide what ISO and f-stop are desirable for your shot and then know precisely how much light is required to reach proper exposure.



Camera

While this is a test about lighting, the camera plays a part as well. We are shooting this test with two Canon C300 MKII’s. The A Cam is shooting with a 35mm Rokinon Cine DS lens square on to the subject, 7′ away. The B Cam is shooting with an 85mm Rokinon Cine DS lens 7′ away at an angle into the fill side of the subject to see how the light wraps her face with the various diffusions and bounces.





Both cameras are at ISO 800, white balance set to 6000°K (the temperature of the Joker 400), and shooting in Rec709. Why Rec709 and not Log? I don’t want to introduce any unnatural augmentation in contrast to the scene by color correcting. Since a 709 image is what we ultimately hope to achieve, I will start and end there with no correction in post.



Diffusion Only Test

In this setup, we are looking at the effects of putting various diffusion materials in front of our light source. These diffusions range from very faint that only affect the hardness of the shadow while maintaining the beam intensity, while others add a lot of overall softness and spread the light beam around. As with any real-life test, there are always minor fluctuations in the exposure and color temperature values. This can happen because of the ambient bounce in the room, the angle of the meter to the source, or the unmeasurable variations in how the materials interact with each other. I arrived at the “Approx. Light Loss & Color Temperature Change” by averaging the values across the entire test. As always, if you need to be precise in your values, conduct your own test in the environment you will be shooting in to take all of these factors into account.


Earlier, we discussed the need to have a consistent distance from the light source to the subject. We always want our “light source,” in this case the diffusion material, to be 6′ from our subject. We are also maintaining a 4′ distance from the light to the diffusion. Here is a diagram illustrating how we set up the test.








Full Silk

The Full Silk, or “White Artificial Silk,” offers the most diffusion of the silks with a significant amount of ambient bounce.


Manufacturer: Matthews

Approx. Light Loss: 1 stop Approx. Color Temperature Change: -290°K (warming)




1/4 Stop Silk

The 1/4 Stop Silk is a lightweight fabric offers a thin diffusion with a significant amount of ambient bounce.


Manufacturer: Matthews Approx. Light Loss: 2/3 stop Approx. Color Temperature Change: -220°K (warming)





China Silk

The China Silk, or “Half Silk,” is a lightweight, slightly translucent natural silk fabric that offers medium diffusion with less ambient bounce than the artificial silks.


Manufacturer: Matthews Approx. Light Loss: 1 stop Approx. Color Temperature Change: -230°K (warming)



Full Grid Cloth

The Full Grid offers the most diffusion of the grids, but with much less ambient bounce than from the silks. The grid pattern in the cloth helps to focus the light, similar to an egg crate in a Chimera.


Manufacturer: Matthews Approx. Light Loss: 1 stop Approx. Color Temperature Change: -340°K (warming)




1/2 (Lite) Grid Cloth

The 1/2, or “Lite,” Grid offers slightly less diffusion than the Full Grid, while still controlling the ambient bounce.


Manufacturer: Matthews Approx. Light Loss: 1 stop Approx. Color Temperature Change: -300°K (warming)




1/4 Grid Cloth

The 1/4 Grid offers a thin diffusion, while controlling the ambient bounce.


Manufacturer: Matthews Approx. Light Loss: 2/3 stop Approx. Color Temperature Change: -210°K (warming)




Frost

The Frost, or “Shower Curtain,” offers a light, soft glow with no ambient bounce. Since it is made of vinyl, the Frost holds it diffusion properties even when wet, making it a great choice for shooting outdoors.


Manufacturer: Matthews Approx. Light Loss: 2/3 stop Approx. Color Temperature Change: -490°K (warming)




Opal (Lee 410)