Just for fun: diffusion materials compared

junkyardsparkle

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A result of some discussion about whether dedicated diffusion materials offered any efficiency benefit over paper towels or packing foam, I decided to actually compare the diffusion vs. light loss characteristics of some things. The test rig was a wooden frame angled over the subject such that the edge of the material tested was resting on the lens, and ~45mm from the fresnel of the Godox TT350 flash at 1/4 power used as a light source. Three shots for each material to control for flash variation, with median selected. Taken with Oly 60/2.8 f/16 ISO 200 ~1:1.3 magnification to approximate real macro shooting. This was done purely in the spirit of curiosity and isn't an attempt to "prove" anything; take it for what it's worth.

First, the bare flash:
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Paper towels:
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Single layer of packing foam:
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Double layer of packing foam:
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Lee Zircon diffusion gels, 810, 811, and 812 respectively:
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The big surprise for me was that the light loss for the high-diffusion gels was not much more than the the lower diffusion ones... good example of why I like to poke the things with sticks instead of making assumptions as much as possible... guess I'll rebuild my flash rig now... :rolleyes:
 
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Petrochemist

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I like the paper towel version more than any of the diffusion gels. If the adage 'you get what you pay for' is true it must have been expensive paper towel! :bravo-009:
 

junkyardsparkle

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I like the paper towel version more than any of the diffusion gels. If the adage 'you get what you pay for' is true it must have been expensive paper towel! :bravo-009:
It's just very expensive in terms of light loss, is the thing. If you have the flash power to burn, though... go for it! I like using small 2xAA powered flashes, or more recently sometimes LED "hot" lights, so I'm personally more enthusiastic about the efficiency of the Lee 810 myself. :D
 

peter_4059

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The Lee 810 does seem to produce nice diffusion while still maintaining similar levels in the other parts of the image. The paper towel is also quite soft light but the attenuation is also noticeable. Are the Lee filter shots just a single layer?

Thanks for posting :)
 

junkyardsparkle

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The Lee 810 does seem to produce nice diffusion while still maintaining similar levels in the other parts of the image. The paper towel is also quite soft light but the attenuation is also noticeable. Are the Lee filter shots just a single layer?
Yep, all single layer except the one double layer of foam. I actually did take a shot of 810+811 layered together:
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Not too impressive, though. The best results from multiple layers of materials, in my experience, comes from placing the second layer somewhere between the direct source and the outer layer... and in fact this seems to be how many commercial portrait softboxes are set up. That's a whole 'nother rabbit hole, though...
 

retiredfromlife

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Would you mind posting a picture of the packing foam you used and its thickness. I have tried a few versions from inwards goods from work and from memory there was a big difference in diffusion and light loss, but unfortunately i did not take notes and it was over a year ago.

I think real life comparisons like you have done are very helpfull
 

junkyardsparkle

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Would you mind posting a picture of the packing foam you used and its thickness. I have tried a few versions from inwards goods from work and from memory there was a big difference in diffusion and light loss, but unfortunately i did not take notes and it was over a year ago.
I didn't grab a picture before packing it back away... it was the really thin stuff that a computer monitor or TV comes sheathed in out of the box, and probably not the best sample, but all I could dig up. I'm sure there are better kinds, maybe somebody with more experience using these (or a variety of kinds around) could do a similar comparison. One of the problems with materials like that is precisely that if you find something that works, it can be hard to tell people how to obtain the exact same kind.

I did also try a piece of 15mm thick stuff such as the actual cushioning in boxes is sometimes made of... the transmission/diffusion ratio was so bad that I didn't include it... it ate light like the paper towels but produced only about half the diffusion. This is that:
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It appears to be two plies, and a single one probably would have been more appropriate, but I didn't have any. If I get my hands on some foam that does seem to perform better at some point, maybe I'll do another run of tests. Incidentally, here's a quick BTS shot I took of the setup, in case anybody else wants to evaluate things they've got laying around:

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Just a sturdy wooden frame I use for various stuff, leaning on a backdrop-covered box, with a roll of tape also under the drop to raise the subject a little. The camera is positioned so that the tip of the lens hood projects just past the surface plane, so that the edge of the various materials can rest on it. A little rolled-up tape on the frame kept the flimsy stuff taut across it for consistent distances.
 

piggsy

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Out of curiosity I tested all of the 4 diffusers that are still alive. I have some others but I would have needed to put them back together or fart around otherwise. All of these use the same kind of packing foam from the same sheet, in different thicknesses and reflector designs.

1
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2
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3
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4
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The 2nd and 3rd ones are my old style internally reflective ones and the 1st and 4th are the more recent direct ones. The 4th is laughable to look at but surprisingly effective and the least hassle to use of any.
 

kevinparis

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maybe I am missing something here... but I thought that the biggest factor in creating diffuse light was the size of the source once diffused relative to the subject as opposed to the opacity of the diffuser?

this was taken with a Rogue Flashbender which is i reckon is less than a foot squared. I was bouncing the Fl600 off that, off camera. The ratio of subject size to light source size and distance means I was throwing a big light source on a small subject

P3040089 by kevinparis, on Flickr
 

archaeopteryx

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I thought that the biggest factor in creating diffuse light was the size of the source once diffused relative to the subject as opposed to the opacity of the diffuser?
Not necessarily sure about biggest, but certainly a major one. If I'm understanding the configuration properly, @junkyardsparkle's evaluation is more the diffuser close to flash case than typical small object arrangements where the diffuser is placed around the object to increase the steradian size of the source seen by the object. I'm unfamiliar with @piggsy's diffusers or test configuration.
 

piggsy

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I don't think there's any complicated thing to understand, it's what happens when you fire at the same scene and power through different materials, and seeing what happens when the material is kept the same but the depth or path to it is changed.
 

junkyardsparkle

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still alive.
I see what you did there. Moving on to portal gun based solutions, now, are we? Can't wait.
maybe I am missing something here... but I thought that the biggest factor in creating diffuse light was the size of the source once diffused relative to the subject as opposed to the opacity of the diffuser?
Simplistically, an apparently larger (as seen by the subject, which could mean actually larger or just closer) source will create softer-edged shadows, due to the light hitting the shadow-producing features at a wider range of angles. This is probably the most important parameter for people shooting models who wear their skeletons on the inside, and don't have eyes half the size of their heads. Most softboxes for this purpose are designed to maximize the light spread over the front panel and minimize any "hot spot" in the middle, to create something resembling the proverbial "north-facing window". The actual characteristics of the specular highlights (the light source being reflected back in a mirror-like way from eyeballs, etc) gets talked about, but is generally somewhat marginalized.

Now, what if your subject is almost entirely shiny? You're going to be looking at a whole lot of those speculars, they become a very prominent part of the final image, so you start giving more thought to the factors that affect their appearance (or disappearance, as the case may be). Starting with a hypothetical default of a tiny pop-up flash directly over the lens axis, you get the classic "crappy flash photo" look: small, hard shadows and hard, small speculars bouncing light straight back at the lens. Making the source larger and moving it to a higher angle improve things a lot... But you may also start thinking about ways to make those speculars less distinct and hard-edged.

To do this, you essentially have to either use something like a light tent, and try to completely surround the object with light, as seen in many "shadowless" product images (or technical illustrations, which may or may not be based on actual photos)... or create a large light source that "feathers" from its edges towards the area producing the most light. You do this by creating something vaguely resembling a hemispherical radiator (a bare bulb flash, or, less efficiently, a normal fresnel flash head firing immediately into a primary diffuser) which then throws its light onto a secondary, subject-facing diffuser, with the spacing adjusted to give the desired radial fall-off, or "feathering". Most of the DIY macro diffusers people make incorporate some amount of this, by design or otherwise, since even a bare fresnel head at a "wide" setting somewhat resembles a bare bulb, even though its trying not to.
So... that's some of the stuff under consideration beyond just size. I have no idea if any of that actually answers your question or not, but hopefully it sheds light on some of the different things people mean when throwing around the word "diffusion" in this non-technical context. As for what's being evaluated specifically in the comparison I posted: I was really just comparing to what extent different light-weight materials suitable for such DIY constructions actually obsure the visibility of the small flash head behind them as such (measured mostly by how "softened" the shadow from the wire at the left side of the frame is) relative to how much light they simply block... what I refer to as "efficiency" (I edited the OP to clarify this a little). Other people using larger flashes probably don't care about this as much, and just pile on the paper towels or whatever, and that's fine, it certainly works, as evidenced by the nicely-diffused-but-comparatively-dark test shot. :D
View attachment 707861@junkyardsparkle's evaluation is more the diffuser close to flash case than typical small object arrangements where the diffuser is placed around the object to increase the steradian size of the source seen by the object
I tried to keep the diffuser<>flash distance at least in the ballpark of the typical DIY construction, but yeah, it's probably at the close end of the range... and certainly different from what you would do in a controlled environment (shooting a collection of bugs stuck on pins or whatnot).
 
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retiredfromlife

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After reading this topic I thought I would try a few things out tonight, and one of the diffusers I tried for the first time is the plastic one that came with the Nissin i40. Previously I been using one of the inflatable diffusers. I am still playing with the led lights that @piggsy linked to in another gear thread.
These lights really help with focusing at night and on the low setting light up spiders webs pretty well.
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Using the led light to enable focusing and help light the web I got the below. EM10ii, Oly 12-40 pro
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The next two I used the Oly MCON-02 close up filter. the thing I like about the diffuser on the Nissin i40 was that the flash was not pointing at the spider at all in the below two shots but enough light hit the spider for a rough shot.
All these were taken in manual mode F11 1/160 flash on TTL -20 compensation on the flash

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Without the diffuser the the spider was just a blown out mess. So this may be a easy and quick to fit diffuser I will keep in my bag now, and that led light has earned a permanent home in my bag.

Link to led light if interested

30W LED COB Work Light Camping Lantern Lamp Waterproof Rechargeable Power Bank | eBay
 
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