diffuser

One more time. With Cubes!

Cue the Cubes!

diffusion-cubes.jpg

Again??? Well, yes. I do these blog posts for myself as much as for my readers. They are my public notebook of lighting tests and experiments.

Here we have three exciting and vibrant still life studies in gray. All three photos were made with the Interfit Deep Zoom Reflector on their Badger Unleashed strobe head. The image on the right was with the bare reflector. In the middle I added the included diffusion sock, and on the left I added an additional layer of diffusion (double-diffused as some might say). I have identified three places in the images to look at and compare.

At point one I want you to look at the primary shadow of the gray cube onto the white cube (scroll down to the bottom of the post for larger versions of the cube photos). With the open reflector there are actually multiple overlapping shadows. The open reflector is not even across. There are multiple light sources: the flash tube, the glass dome, the walls of the reflector. Each is slightly different in brightness and casts its own shadow. Adding a diffuser homogenizes the light into one large source and eliminates the hot spot. You can see this in these photos of the face of the reflector.

Bare reflector, single layer of diffusion, and double layer of diffusion

Bare reflector, single layer of diffusion, and double layer of diffusion

Looking closely at the cubes you should still be able to see that there is a primary hard edged shadow at point One and that doesn’t change between the three photos because the overall size of the light has not changed. Remember, for a light to be softer with more gradual shadows the light has to come in from many directions. Once you have added a diffuser it won’t matter how many extra layers you add, it will not make the light any softer. The diffusion will alter the contrast of the scene as it spreads the light out in a wider pattern allowing it to bounce off of items in the environment such as the floor, walls, ceiling, etc. filling in the shadows and making them less dense. Less dense = less contrast. But the shadow edge, the quality, does not change.

Point Two is similar. The open reflector shadow is deeper. Adding the diffusion evens out the light from the reflector and fills in some of the shadow. But again the primary shadow edge is about equal.

Point Three is the most dramatic difference where the diffuser made the light larger and able to wrap around the side of the black cube to provide more illumination so you can see the back of the table top.

What I really want to concentrate on are the differences between the images with single and double diffusion. Or is differences the wrong word as they are actually very similar, almost identical in appearance. The main difference being that I had to open up the aperture a stop to maintain the proper exposure.

I hope this helps show that adding more and more layers of diffusion will not soften the shadows in your photographs. That comes from making the light larger. Multiple layers of diffusion require more light output or allow you to cut down the amount of light if you cannot power it down or don’t want to change your f/stop.

Click on each of the photos below for a larger version.

Open Reflector

Single Diffuser

Single Diffuser

Double Diffuser

Double Diffuser

Diffusion yet again

I just can’t stop…

In my last post I mentioned that adding diffusion at the same size as the light source will not soften the light (change the shadow edge transition), but will change the contrast. Adding an additional layer (or more) will still maintain the same light quality, but spread it out a little bit more and also lose a lot of power.

That got me to wondering just how much light is bouncing around the room to add to lower the contrast and fill in those shadows. Obviously in a very large studio with black floor, walls, and ceilings there will be nothing to bounce off of. Similarly if working out doors in an open field there will be no extra fill. But I am working in a modestly sized room with an 8-foot white ceiling, a light natural wood floor, and white walls.

Time for another test!

The Interfit Deep Zoom Reflector

The Interfit Deep Zoom Reflector

Here are three images made with the Interfit Deep Zoom reflector. The first image is with the “bare” reflector. Next is with the included diffusion “sock” and the third image has a sheet of diffusion material added to the front of the modifier for “double-diffusion.” I kept the camera settings at ISO 100, SS 1/160 sec., and F/9 so that the ambient light effect on the image would remain the same. I raised the power of the flash in each image to compensate for the diffusers and to maintain the same flash exposure.

Click to enlarge

Here you can see that the shadow edge changes slightly from bare reflector to diffused reflector as the light is homogenized from multiple sources (flash tube, glass dome, reflector) all contributing their own shadows to one source (the diffusion material). And you can see that the shadows open up a little bit and the background gets a little bit brighter. Comparing the second image (single diffuser) to the third (double-diffuser) note that the shadow edge that determines the light quality is exactly the same. The diffusion is the same size as the light. If the light size doesn’t change the quality of light doesn’t change. What changes here is how much power you need from your lights to compensate for the light loss from the multiple diffusers. Again, don’t confuse contrast with quality (hard or soft) of light.

Now go out and light up your world!

John



Diffusion Confusion (take 4!)

Diffusion will be my epitaph

So I lied last time. It is more than once a year that I find myself writing about diffusion. But i still see so much misunderstanding about this topic. This time I will try to be short and sweet.

Diffusion scatters light. Diffusion can come from passing light through a translucent material (such as a white shower curtain, or a scrim, or diffusion material from the camera/cinema store) or by bouncing the light off of a mat surface (a painted wall, a sheet of foamcore, a sheet of art board, etc.). Here I will be concentrating on shining the light through translucent material placed right on the light source (or the metal dish reflector on the light source).

As I said, diffusion scatters the light. But it doesn’t soften the light. Diffusion possibly lowers the contrast as it scatters the light that will then bounce of of nearby surfaces like the floor, walls, and ceiling. This will cause the shadows to be filled in or lighter in density. But the shadow edge transition won’t change if the size of the light source doesn’t change. Don’t confuse contrast with hardness (quality). In a small studio space this is more apparent than in a large space (in the large space the light has to travel farther to a surface to bounce off of to come back and fill in the shadows).

How many layers of diffusion did you use???

It pains me when I read someone saying the put 3 or 4 or 5 (or more!) layers of diffusion over their light to soften it. All they actually did was lower the output of the light, causing them to either have to use a more powerful light, go to a higher ISO, or work at a wider aperture than they might have wanted to. But the one thing they did not do is change the shadow transition to make the light softer. To make the light softer would require using a diffuser that is much larger than the light source. If the diffuser and the light are the same size the light quality remains the same. The time to use double diffusion is if your diffusion material is rather thin and you can see the hot center spot of a light pointed through the material. (NOTE: This is separate from the concept of a softbox or octabox that has an inner and outer diffuser. In that case the inner diffuser’s job is to spread out the light from the strobe to completely illuminate the larger front panel diffuser and is not the same thing as double diffusing the front of the softbox or octa.)

7-inch reflector without and with diffusion

The opposite of diffusion is to narrow the light with some sort of baffle. This could be a snoot, a set of barn doors, or a honeycomb grid. I want to talk about grids here for one big reason. I often see photographers mixing a grid with a diffuser by putting the diffuser between the grid and the subject. I am not sure what they are trying to accomplish with that other than again losing a lot of light (2 stops or more in my testing). And they also lose the effect of the grid. If you feel you need a diffuser with a grid, you need to place the diffusing material between the flash tube and the grid, not in front of the grid. See the Deep Zoom Reflector examples photos later in the article.

First, let’s go to the standard 7-inch reflector that is common to most strobe systems. In the accompanying photos (click on the photo to see a larger version) I have used the 7-inch on its own, then with one layer of diffusion clipped on, and then with two layers of diffusion clipped on. There are a few things to notice. First is the large shadow on the background. Without diffusion there are actually multiple shadows with distinct edges. This comes from the combination of the flash tube itself, the reflector behind the flash tube, and the dish reflector around the flash tube each putting out a little bit different amount of light from their different sizes. When we add diffusion the light is homogenized or evened out so the shadow on the wall is more even. Then look at the shadow of the nose and the highlight on the tip of the nose. By adding the diffusion (one layer, two layers, or a dozen layers) we do not see any changes to these from one photo to the next. The edge of the shadow is still the same hardness and the highlight is still the same brightness in relation to the overall exposure. As noted above the density of the shadow might be a little brighter from light bouncing around the room, but that doesn’t affect the edge quality of that subject. If we want to lessen the brightness of the highlight on the nose one solution is to bring the light in closer, which will make the light bigger and cause it to fall off quicker (See! Everything in photography is interdependent and full of trade-offs). As a specular reflection the brightness will actually stay the same while getting larger, but the exposure on the rest of the face will also get brighter and we will power down the strobe to compensate for that which will then also bring down the brightness of the hot spot.

7-inch reflector bare, with a grid, and with a grid + diffusion

Now let’s look at combining a grid with diffusion. Three examples again this time. The first is with the same one we saw with 7-inch dish in the above examples. Then the 10-degree grid is added which limits the spread of the light for a more dramatic look and deeper shadows because there is less light bouncing around the rest of the room. This is the look I suspect that everyone is looking for with the grids. But then some people put a diffuser over grid. And look what happens when the diffusion material is placed over the grid—the diffusion material does its job (scattering the light into a wider pattern) and completely obliterates the effect from the use of the grid. Take a look at the diagram at the bottom of this post. And that is at the cost of two or more stops of light (translating into using more battery power if you are using a portable battery powered system). If you do feel the need to diffuse the light when using a grid you need to place the diffusion between the flash tube and the grid, not in front of the grid (yes, I am repeating myself for emphasis). We will take a look at how that works in the next set of examples below.

Diffusion scatters light

Baffles restrict light

Don’t confuse light contrast with light quality

Deep Zoom Reflector examples

One more example, this time with the Deep Zoom 11-inch reflector kit from Interfit. The Deep Zoom kit comes with a set of three grids (10-, 20-, and 30-degree) and a diffusion sock. Six examples this time. First we see the Deep Zoom by itself providing a nice crisp look. Adding the diffusion sock lowers the contrast, but retains the same shadow edge quality. Next I put on the 10-degree grid providing a more dramatic look with falloff of light across the background and a bit more contrast. Then I tried the grid with the diffusion sock over the grid and POOF there goes the grid effect that you spent good money on to purchase the grids. The next thing to try was with the sock behind the grid, between the flash tube and the grid. We get the drama back, but with a bit less contrast. So, while we’re at it, what happens wit with the sock behind the grid and a sheet of diffusion material in front of the grid. Again we can see that by adding diffusion in front of the grid we are negating the effect of the grid.

In all six examples we need to take a look at and compare the transition edge of the nose shadow. By now I hope that you don’t really need to look at it to know that it is going to be the same because the size of the light didn’t change between photographs.

So, to recap…

Diffusion scatters light in all directions and makes it cover a wider area. As the light is scattered and some is absorbed by the diffusion material you will lose some power.

Diffusion material can be specific products like those from Lee and Rosco. Or it can be a sheet of tracing paper or a bedsheet or a frosted shower curtain. Here I am assuming that the diffusion is dense enough that you won’t see a hot spot from a light shining through it. This is usually called a full-stop diffuser. Your diffusion material should be neutral in color, but often isn’t. That white shower curtain might contain brighteners that make it cause the light to be more blue, or it might have yellowed with age. Be prepared to have to do some color compensation when processing your raw files.

The opposite of a diffuser is a baffle (though I am befuddled as to why some softbox manufacturers and photographers call their scrims and the inner diffuser on their softboxes baffles). Baffles restrict the flow of light. Common examples are snoots, barn doors, and grids. Grids maintain the shadow edge while restricting the coverage of the light. Hard grids are available for use with metal reflectors like the 7-inch, the Deep Zoom, and beauty dishes. They are rigid with a honeycomb pattern of openings and snap onto the front of the reflector. They usually come in densities from 5-degrees to 40-degrees. The lower the number the narrower the light coming out of them. Soft fabric grids are available for most softboxes and octa boxes. They are usually around 40-degrees and allow you to have a large directional soft light.

Don’t confuse contrast (the difference between the light and dark areas of your image) with quality of light (how quickly the shadows transition from dark to light). While thinking about that, also do not confuse brightness with harshness. Moving a light in closer makes it brighter, but also softer as it becomes bigger in relation to the subject (or as seen by the subject). The exception to this is when using hard grids. Because the light rays are restricted by the honeycomb only the center rays from the light going through the grid will reach the subject, making the light appear smaller as it is brought in closer.

Expanding on this illustration from a  previous blog post

Expanding on this illustration from a previous blog post

Well, thanks again for indulging me and reading through my thoughts on studio lighting. Now go out and make some photographs! Until next time…

Cheers!
John Cornicello



Continuing the Diffusion Discussion

Size still matters

In recent posts about diffusion I have been concentrating on small light sources such as speed lights or the "standard" 7-inch metal dish reflectors on studio strobes. But what about larger sources? I was recently gifted a Speedotron 20-inch metal dish reflector. As I am no longer using Speedotrons as my main lights I adapted the reflector to an S-mount for use with my Interfit Photographic lights. This post contains affiliate links and I will be compensated if you make a purchase after clicking on my links.

As I started testing this franken-reflector I noticed that the light was harder than I expected. A look inside the bowl gave some cues as to what was going on. Speedotron lamp heads have large protruding flash tubes and/or flash tube covers. This pushes the light source out in front of the mount on the reflector, allowing the light to completely fill the bowl. The bulbs on the Interfit, though they do protrude, are not quite as long as the Speedo tubes. So most of the light was coming straight out of the flash going forward and not spreading out quickly enough to fill the bowl. 

I did some cutting and drilling to change the position of the S-mount to try to push the flash tube a bit further into the bowl. That still wasn't enough. A quick experiment using a 12x12-inch sheet of diffusion gel in the shape of a dome over the flash tube confirmed what I needed. My first thought was to find a Tupperware bowl around the size of the pyrex flash tube cover, but a quick look through kitchen cabinets didn't turn one up. That got me to thinking that people used to call some speed light flash diffusers Tupperware. And I remembered that I had a very old one of those made of a hard plastic that was specific to a speed light I no longer had. I quickly found that diffuser and a hack saw and went to work.

After cutting off the bottom of the diffuser I was relieved to find it to be exactly the right size to fit in the S-mount. A bit of hot glue and clear caulk and it was fixed in place, ready for testing. And some disappointment. The light was still harder than I expected. Even with the diffuser in place, most of the light was concentrated in the middle and not filling the bowl. Then I remembered that there was a second piece to the diffuser, a dome that snaps onto it. I quickly located that and voila, the second test did show a noticeable change in the shadows and more light "wrapping" around to the side of the subject (notice the ear is brighter). Now the diffuser was doing its job--making the light spread wider to fill the bowl of the reflector. The diffuser itself didn't make the light softer, but it did make the light source larger which did soften the light. 

The next option was to add a diffusion sock over the entire reflector. This has the effect of spreading out the light across the full 20-inches of the bowl making the light source even larger and more even across the surface. Again the diffuser spread the light and evened it out. The last test was to try the sock with and without the dome inside the reflector. This showed a subtle change. With the dome the light source appeared a bit larger, as seen by more light reaching the ear. But the shadow transition was pretty much the same with and without the dome. It was just that with the dome more of the bowl was lit and the light wasn't as directional.

Let's look at the tests (click on the image for a larger version)...

Here are side views of the interior of the modified 20-inch bowl reflector with and without the dome on the diffuser. I made one more modification, not shown here. I drilled a series of small holes around the edge of the snap on dome to help the fans in the strobe head be more efficient.

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Safety First
IMPORTANT: DO NOT TRY THIS WITH A STROBE THAT USES TUNGSTEN OR QUARTZ MODELING LAMPS!! I was able to do this with the Interfit strobes because they use relatively cool running LED modeling lamps. For comparison, the 60-watt LED in the Honey Badger is brighter than the 250-watt quartz-halogen modeling lamp in my older strobes. But the LED's temperature after being on for hours remains around 85-degrees F while the quartz bulbs reach temperatures over 300-degrees F in a matter of seconds.


So, you might ask, what is the point of all this today. It is all part of trying to dispel myths around diffusion. It is easy to look at the photos and decide that the various diffusers changed the quality of the light. But it still comes back to the fact that the quality of the light is determined by the size of the light. In these examples the diffusion spread the light to better fill the bowl of the reflector. Without any diffusion the 20-inch reflector is bright in the middle and darker around the edges, making it appear smaller than its actual size. As diffusion is added the light spreads out to fill the bowl, making it appear to be its full size.

 

 

Baffled by Baffles

Is it a baffle or a diffuser?

Being my pedantic self again here. And maybe this use of the term baffle has been going on for a long time and I've just ignored it. But recently I have seen a lot of photography sites using the terms baffle and diffuser interchangeably. I see references to the "inner baffle" on a softbox (try this Google search on softbox baffle). One ad mentions a "white diffusive baffle." This isn't just photographers writing about light, it is also in the descriptions of modifiers on the websites of lighting companies.

Let's start with the dictionary and the definitions of baffle and diffuser...

Baffle 
noun
a device used to restrain the flow of a fluid, gas, or loose material or to prevent the spreading of sound or light in a particular direction.

Diffuser
noun
a device that spreads the light from a light source evenly

From the definitions, these seem to be opposites. A baffle would be more akin to a grid on a light that restricts the light to make it more directional and prevents the light from spreading out. The inner translucent panel in a softbox is diffusing the light and spreading it out and trying to avoid having a directional hot spot. The outer diffuser does the same thing. And some photographers put multiple diffusers over the outside of their softbox/octa/softlighter. None of these things are acting as a baffle in my mind.

Diffuser vs Baffle

Diffuser vs Baffle

Am I just the old curmudgeon who can't get with the new terminology? Or should we be more precise in our descriptions?