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Archive 2008 · Flash diffuser materials comparison
  
 
LordV
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p.1 #1 · p.1 #1 · Flash diffuser materials comparison


Awful weather today so I played with some different diffuser materials on my coke can. Materials all commonly available in the house.
The amount of diffusion not suprisingly seemed directly related to the light loss. The light loss was estimated by looking at a series of shots taken with the flash in manual (ie 1/64,1/32,1/16,1/8) but the comparison shots are all ETTL.
The target is a raisin with two board pins taken at 1:1,F11, ISO200,1/200th.

I tend to use either kitchen towel or disposable table cloth

Brian V.

click on pic for larger size





Nov 01, 2008 at 03:00 PM
n0b0
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p.1 #2 · p.1 #2 · Flash diffuser materials comparison


excellent comparison Brian. Have you tried lowering the shutter speed to 1/160 and see what that does to the light?


Nov 01, 2008 at 03:28 PM
LordV
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p.1 #3 · p.1 #3 · Flash diffuser materials comparison


n0b0 wrote:
excellent comparison Brian. Have you tried lowering the shutter speed to 1/160 and see what that does to the light?

Thanks - this was mainly about working out a test sytem - I tried with just the raisin first and got virtually no difference. Dropping the shutter speed should make no difference at all as I suspect the flash durations were of the order 1/2000 to 1/10000th sec and would thus be the effective shutter speed.
Brian V.



Nov 01, 2008 at 03:52 PM
Dalantech
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p.1 #4 · p.1 #4 · Flash diffuser materials comparison


n0b0 wrote:
excellent comparison Brian. Have you tried lowering the shutter speed to 1/160 and see what that does to the light?


At life size, F11, and ISO 200 indoors there wasn't any ambient light being registered by the sensor n0b0, so the shutter speed doesn't make any difference -if the flash didn't fire the frame would be completely black. Also keep in mind that changing your shutter speed will never alter the duration of the flash -changing the ISO and / or the aperture will since the flash duration will always be shorter than the shutter at 1/250 and slower shutter speeds.

Excellent test Brian with some really interesting results. I wonder if you could get the same level of diffusion with the paper towel if you used a diffuser plastic that's designed to diffuse the light from a flash and at the same time lose less light. When I was out shooting at 3x today my MT-24EX was making a short popping noise every time it went off and that was at ISO 100 (I was shooting at ISO 200 there for a while to drop the flash duration, but it's not necessary now that I've changed my diffuser).



Nov 01, 2008 at 04:24 PM
Kenj8246
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p.1 #5 · p.1 #5 · Flash diffuser materials comparison


Ok, I know I'm gonna feel stupid when you answer this, but how did you arrive at the approximate light loss per diffuser?

Kenny



Nov 01, 2008 at 04:25 PM
Dalantech
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p.1 #6 · p.1 #6 · Flash diffuser materials comparison


Kenj8246 wrote:
Ok, I know I'm gonna feel stupid when you answer this, but how did you arrive at the approximate light loss per diffuser?

Kenny


By how much the manual flash exposure changed relative to the bare flash.



Nov 01, 2008 at 04:33 PM
Kenj8246
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p.1 #7 · p.1 #7 · Flash diffuser materials comparison


Dalantech wrote:
...By how much the manual flash exposure changed relative to the bare flash.


How much the manual flash exposure changed relative to the bare flash measured by what? How?



Nov 01, 2008 at 04:38 PM
LordV
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p.1 #8 · p.1 #8 · Flash diffuser materials comparison


Kenj8246 wrote:
How much the manual flash exposure changed relative to the bare flash measured by what? How?


In manual the flash changes by 1 stop intervals ie 1/64. 1/32,1/16th etc so by taking a series and then looking at how far off the exposure was in RAW processing (DPP), I can work out the light loss relative to the no diffuser.
Brian V.



Nov 01, 2008 at 04:44 PM
Dalantech
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p.1 #9 · p.1 #9 · Flash diffuser materials comparison


Kenj8246 wrote:
How much the manual flash exposure changed relative to the bare flash measured by what? How?


If the bare flash was at 1/4 power for a good exposure (comparing the same shot to one taken in E-TTL mode -if the two match then you know that the flash is firing at 1/4 power when in E-TTL mode) and then if the diffuser material caused the manual exposure to change to 1/2 power (again comparing the 1/2 power manual against an E-TTL exposure to make sure the two were the same) then the stop loss would have been 1. I should have let Brian answer

@ Brian: Any difference in the red channel between the different diffuser materials?



Nov 01, 2008 at 04:46 PM
LordV
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p.1 #10 · p.1 #10 · Flash diffuser materials comparison


Dalantech wrote:
At life size, F11, and ISO 200 indoors there wasn't any ambient light being registered by the sensor n0b0, so the shutter speed doesn't make any difference -if the flash didn't fire the frame would be completely black. Also keep in mind that changing your shutter speed will never alter the duration of the flash -changing the ISO and / or the aperture will since the flash duration will always be shorter than the shutter at 1/250 and slower shutter speeds.

Excellent test Brian with some really interesting results. I wonder if you could get the same level of diffusion with
...Show more

Honest answer John is I don't know, obvious thing to try now is some other materials to see if I can get away from the light loss/diffusion line that seems to exist in these shots. There's a few other things I want to try including multiple layers of the high pass materials.

Brian V.



Nov 01, 2008 at 04:51 PM
 

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Dalantech
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p.1 #11 · p.1 #11 · Flash diffuser materials comparison


One thing that I noticed Brian was with some diffuser materials I was always blowing the red channel (the Puffer diffuser was a prime example) and I think there may be a relationship between the flash duration and the red channel with longer flash durations pushing the red channel more. With my current diffuser I have a lot of room to increase the exposure before the red channel is all the way to the right.

I'm also using a very low level diffusion material (a light frost) before a heavier diffusion material and that seems to work pretty well. Maybe try onion (or tracing) paper before the milk bottle...



Nov 01, 2008 at 05:33 PM
LordV
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p.1 #12 · p.1 #12 · Flash diffuser materials comparison


Dalantech wrote:
One thing that I noticed Brian was with some diffuser materials I was always blowing the red channel (the Puffer diffuser was a prime example) and I think there may be a relationship between the flash duration and the red channel with longer flash durations pushing the red channel more. With my current diffuser I have a lot of room to increase the exposure before the red channel is all the way to the right.

I'm also using a very low level diffusion material (a light frost) before a heavier diffusion material and that seems to work pretty well. Maybe try
...Show more

Maybe you should try paper based diffusers - there is some suppresion of the red channel in all the paper based diffusers. So if there is a relationship with flash duration it's inverse (ie longer flash durations= less red) in these tests. Should add I did adjust the colour temp of them all to the same value during RAW (not sure it was different in the first place though)

Brian v.




Nov 01, 2008 at 05:47 PM
Dalantech
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p.1 #13 · p.1 #13 · Flash diffuser materials comparison


LordV wrote:
Maybe you should try paper based diffusers - there is some suppresion of the red channel in all the paper based diffusers.


As odd as it might sound Brian that's one of the reasons why I'm using the 1/8 CTO. I thought that a CTO gel would make the red channel worse, but it gives me the warmth I'm looking for without having to push the saturation or the white balance. The Bogen diffuser kit that I recently picked up also helped, since the diffuser plastic in it doesn't amplify the red channel as badly as the Sto-Fen plastic did.

Sorry Brian, but at a 2 stop loss that paper towel is doing more to block the light from your flash than it is diffusing it...



Nov 01, 2008 at 05:54 PM
LordV
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p.1 #14 · p.1 #14 · Flash diffuser materials comparison


Some more tests together with red channel histograms. Oddly this time I don't think the red channels changed significantly between tests. The shots were all taken with manual flash power. The wide angle flash diffuser gives a somewhat odd result. Think I'll try the 3-layer styrofoam packing for a while and see how it does.

Brian V.

Click on pic for larger version go full screen and click again




Nov 02, 2008 at 08:15 AM
MichAg92
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p.1 #15 · p.1 #15 · Flash diffuser materials comparison


I don't see a whole lot of difference among them, not even really sure the no diffuser shot offends me- only a slightly greater area of blown-out hightlights...this is leading me to believe that the diffusion itself isn't nealry as important as the area increase of the source of light if your subject is bigger - not sure that at about 1cm2 (assume you have an average size raisin), that you really need to diffuse the light...


Nov 02, 2008 at 11:47 PM
lextalionis
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p.1 #16 · p.1 #16 · Flash diffuser materials comparison


OMG...so "someone" is using a CTO gel...hummm...very interesting. I love these threads. Thanks for posting this Brian.


-Roy



Nov 03, 2008 at 01:03 AM
LordV
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p.1 #17 · p.1 #17 · Flash diffuser materials comparison


Thanks for the comments Roy and Amy.

I may have confused things slightly by taking the second set of shots all with manual flash as I was primarily interested in looking at the light loss.

Amy you are correct- I was looking for a situation where the highlight on the pin head was not blown. No way to avoid having a highlight at all with this setup. This seems to require the flash diffuser material behaving as a larger light source than the flash head itself so "spreading the light". Think I would have needed something like a flash reflecting umbrella to evenly light the whole pinhead.
Overall I was looking for a simple test target subject to rapidly compare diffusers with and a method of assessing the light loss associated with them.

Thinking more about this it is possible that I'm looking for different properties than john as I want the diffuser material to act as both a light scattering medium but also as a secondary light source itelf. Bit like the effects of clouds on the sun as a light source.

Brian V.



Nov 03, 2008 at 07:30 AM
Dalantech
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p.1 #18 · p.1 #18 · Flash diffuser materials comparison


@ Roy -I like to get the effect I'm looking for with the shutter release

@ Brian: I thought you were using a coke can cut and reshaped with tape on the outside to hold the shape. If that's the case then your outer diffuser should be the light source, since all the light from the flash is being forced out the front. I'm doing something similar, although on a smaller scale, with the Sto-Fens -I've used gaffers tape on the outside to stop the light from leaking out the sides. Not as reflective as the coke can you're using, but still forcing the light out the front of the diffuser.

One of the reasons why you might not be seeing much of a change in your specular highlights is due to the stop loss -the flash duration is four times longer with the diffuser than without it. Even though the final exposure is the same the longer the flash is on the greater the chance that reflective surfaces are going to blow out -flash duration and glare are directly proportional. Look for something that will diffuse the light but block a stop or less and you should see a big change in the specular highlights...

One other trick to try: Make the outer diameter of your diffuser smaller. For life size and higher shooting you just don't need a huge diffusion surface, and the more spread out the light is the weaker it is -and the flash duration has to go up to compensate. I think there is a point of diminishing returns to diffuser size when shooting macro -were the point lies I don't know and I think it would have a lot to do with the light source. Also a large diffuser is going to throw light where you don't need it -lots of white balance problems when you have a scene that's got a mix of colored light sources due to all of the stuff that's reflecting the flash light back onto the subject.



Nov 03, 2008 at 09:15 AM
Sanlameer
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p.1 #19 · p.1 #19 · Flash diffuser materials comparison


How does your setup work? Picture please.

Ben



Nov 03, 2008 at 12:53 PM
LordV
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p.1 #20 · p.1 #20 · Flash diffuser materials comparison



John - I'm not particularly bothered about flash durations apart from being able to take upto say 5 shots without the flash recycling. Think we are operating from different POVs (seems quite normal) - I want a largish light area on the flash primarily to expand the bright areas on reflective surfaces and therefore diminish the light intensity in them. This is especially true for large curved surfaces eg eyes and some bodies. I have tried a much narrower diffuser which is fine for shots around 3:1 or higher but it didn't perform anywhere as near as well as my larger one at lower mags. In many of the shots I take I rely on light scattering from the background - I actually like the effects it can give

Brian V.



Nov 03, 2008 at 01:15 PM
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