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Thread started 16 Jan 2016 (Saturday) 18:57
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Bond paper diffuser

 
Dalantech
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Post has been edited over 1 year ago by Dalantech.
Jan 30, 2016 17:07 |  #31

Archibald wrote in post #17879543 (external link)
Same here. :-)
Nice shot, great detail as you said. That's very good for f/16. How was it lit? There seem to be two main light sources, diffuse from above and more intense from the right.

Key and fill configuration -the same that portrait photographers use. The "A" flash head on a Kaiser adjustable flash shoe firing almost straight down, the fill at about 3 O'clock (to keep the shadows from being crushed).

IMAGE: https://farm1.staticflickr.com/717/22788287677_e0e3323d37_c.jpg
[IMAGE'S LINK: https://flic.kr/p/AHHV​ZF] (external link)Mantis Portrait I (external link) by John Kimbler (external link), on Flickr

Same as that shot.

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Wilt
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Post has been last edited over 1 year ago by Wilt. 2 edits done in total.
Jan 30, 2016 17:36 |  #32

Dalantech wrote in post #17879544 (external link)
To diffuse means to spread out. The two terms are the same. We're in a discussion about diffusion, and if you have something to add to it then great. Post images showing your diffusion -prove that you know what you're doing...

About 1.5x in a range that's the worst for my diffusers (more distance between them and the subject):

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[IMAGE'S LINK: https://flic.kr/p/Dasf​13] (external link)Is it Safe Yet? II (external link) by John Kimbler (external link), on Flickr

Again the proof is in the images...


Huh? you seem to sound as if I challenged what you said. NOT! Post 24 was total agreement, I merely added more information on the points you brought up!


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Dalantech
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Jan 31, 2016 01:41 |  #33

Wilt wrote in post #17879575 (external link)
Huh? you seem to sound as if I challenged what you said. NOT! Post 24 was total agreement, I merely added more information on the points you brought up!

Then I apologize. It seemed like you were trying to separate the terms.


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SteB
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Jan 31, 2016 11:08 |  #34

Archibald wrote in post #17877746 (external link)
Thanks for the info.

With these diffusion materials, there seems to be an inverse relationship between transmittance and diffusion (light scattering). For the softest light one needs the densest material. I guess it's because light scattering in these sheets is random. What we need is a sheet that gives great transmission and also great light scattering. The only stuff I can think of that does that is the pull-out plastic things on the bigger Canon flashes that Canon calls a "wide panel". Those wide panels don't scatter light randomly, they refract the light in an orderly manner. If only larger sheets like this were available.

I'm guessing packing foam and milk bottle plastic, as well as the paper and gel and vellum, all have about the same scattering:density ratio. You suggest that vellum is better, though. Maybe it is time for me to acquire some of this stuff and have a look.

I admit I've never quantified the abilities of diffusion material. I have tested lots of materials but I tend to just do it subjectively. However, my tests have seemed to contradict the intuitive idea that the thicker and more opaque the diffuser material, the better the diffusion abilities. In fact I have found some of the best diffusion materials have high light transmittance. A few years back and I was using this material from computer dust covers. It was semi-transparent, and if you pressed it hard down on printed text you could read it. I've not liked the milk bottle plastic I've used. It soaks up a lot of light and often tends to impart a colour cast.

However, this is not so much about diffuser materials and they are a bit of a red herring. It is about light modification. Light modification is much more important than the diffuser material. There is a limited amount a diffuser material can do to modify light.

As I discovered in comprehensive tests I did, which I won't go into here, specular reflections are not caused by a lack of diffusion, and this is a blind alley. Specular reflections are a reflection of the light source on a curved shiny surface. To decrease specular reflections on a curved shine surface, you have to make the diffuser area large, and so the light wraps around the subject. This is the purpose of these curved concave end of lens diffusers, which as far as I know, I was the first person to ever use them on a portable flash rig. I didn't just randomly put a curved bit of material on the end of a lens, I thought about it from first principles i.e. how the light behaved in the close up region. I realised that to get a large diffuser surface area relative to the subject, it had to be curved to wrap around the subject, and this also greatly increases the surface area relative to the subject. If you flatten your end of lens bond paper diffuser, you will see it is quite large in area.

The problem with a flat faced diffuser is that as you make it bigger, with a small subject the edges are a lot further from the subject. This means the light from the edges has to travel much further from the edges, it spreads out and decreases in intensity. The short story is this effective makes the centre of the diffuser brighter than the edges, which does not stop specular reflections. The inverse square law means as the distance doubles it is 2 stops less intense because the light has to cover 4x the surface area. The inverse square law refers to point light sources. However, a diffuser face is simply a myriad of point sources, and so it still applies. Because your flash diffuser is often only a few cm from the subject in macro flash, and a large diffuser can be easily 15-20cm wide, you can see how much further the edges are relative to the centre. What's more when a flash hits a flat diffuser the centre tends to be brighter than the edges anyway.

Another advantage with these curved concave faced diffusers is that the light bounces around in the curved face, providing extra fill in from the sides, increasing the wrap around characteristic of the light.

I have actually tried out bond paper in my experiments with diffuser materials about 5-6 years back. I stopped using it, along with other papers, except for velum paper because it absorbed so much light, and didn't appear to have any better diffusion characteristics to diffuser materials which transmitted more light. I would strong recommend you check out "diffuser gel", just Google it. It is relative cheap. In the UK it only costs about £5 UK pounds for a roll. You can make a lot of diffusers from one roll. It's not necessarily a lot better than velum paper or some other diffuse materials. But it is the right thickness to create some rigidity, whilst still being flexible, and it is waterproof and durable.




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SteB
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Jan 31, 2016 11:17 |  #35

Wilt wrote in post #17879302 (external link)
Good opportunity to reuse past POTN illustrations.
This photo sequence illustrates how a 'diffuse surface' of the Stofen does have some minor affect on the penumbra of the shadow, but its limited size has little effect on the overall harshness of the shadow. A very small (5x7.5" softbox) is also shown for comparison.

Yes, that's right and the point I was making in my other comments. I did some test shots about 6 years back demonstrating that StoFens had only a minor effect on soften specular reflections on curved shiny surfaces on macro subjects, compared to the bare flash head. Diffusion is only a sub-part of light modification in macro photography. There is only so much you can do to diffuse light from the same surface area, and you need to increase the surface area to produce better light with less specular reflections and softer shadows. However I also realised that at very close distances if you made a flat fronted diffuser bigger, the edges where much further from the subject. Even if theoretically the light was even distributed over the whole diffuser face it would make the centre relatively much brighter as the light from the edges of the diffuser would have to travel relatively much further, and the light drop off over distance would make this light much dimmer. This is where I got the idea of using a curved diffuser on the end of the lens. It not only wrapped around the subject, but it prevented that problem, gave you a much larger diffuser surface area, and the light bounced around inside it to soften the shadow even more. With this type of diffuser I can over-expose up to 2 stops or more, and still recover the highlights with RAW files.




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Archibald
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Jan 31, 2016 14:08 as a reply to SteB's post |  #36

Thanks for the description of the concave diffuser and the reasons for the shape. I had read about the concave diffuser but didn't know about the background.

As for the gel you mention, it is possible I already have some of it or an equivalent material. It is a big roll suitable for rear projection. It transmits much more light but doesn't diffuse to the same degree as bond paper - in other words has a hotspot in the middle. It is a good alternative though, and it is not always necessary to reduce specular reflections (many subjects don't need it).

I made the current diffuser out of paper to make it cheap and portable, and so I can make a new one anywhere if needed. I have not tried to optimize it for light transmission or softness, but I think it will work OK.


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mfturner
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Jan 31, 2016 16:08 |  #37

I agree with SteB that some of the best diffusion materials have high transmissivity, my favorite is kitchen waxed paper, partly because we have tons of it. But it does not have much structure, and for field expediency bond paper is easy to find. So right now I am playing with a two stage system, wax paper taped to my built in flash whose purpose is to widen the angle of coverage, then a hand held sheet of bond paper curving along the length of the lens and up at the end of the lens to re-diffuse light.




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SteB
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Jan 31, 2016 18:03 |  #38

mfturner wrote in post #17880693 (external link)
I agree with SteB that some of the best diffusion materials have high transmissivity, my favorite is kitchen waxed paper, partly because we have tons of it. But it does not have much structure, and for field expediency bond paper is easy to find. So right now I am playing with a two stage system, wax paper taped to my built in flash whose purpose is to widen the angle of coverage, then a hand held sheet of bond paper curving along the length of the lens and up at the end of the lens to re-diffuse light.

This is what I was going to suggest to Archibald. A 2 stage diffusion system. On my Canon 270EX flash set up, where I have a virtually identical conical end of lens diffuser I have 2 pieces to attach to the flash to pre-diffuser the light before it hits the conical end of lens diffuser. I have a bounce card, either the commercial one I posted a photo of, or a smaller DIY one, made out of "plasticard". This is white non-expanded polystyrene sheet sold in different thicknesses for use in model making. Then I have a right angled piece of diffuser gel that attaches under the flash head with self-adhesive velcro tape.

I have tried waxed kitchen paper and tracing paper as diffusion material. As you say, whilst it's got good diffusion properties, it lacks the stiffness. This is why I prefer velum paper or diffusion gel as it has enough rigidity when curved to support itself. Another dodge I've used is to use the clear thin plastic from a 2 litre water of fizzy drinks bottle, and create the diffuser shape with that. Then you can put the diffuser material on it. I use velcro hoop and loop self-adhesive tape for attaching things. It sticks on to most surfaces, but you can remove it and the residue so it leaves no marks. The advantage of using it is that you can make your diffusers modular, and have different thicknesses or size of diffusers for different purposes. I use silver and gold coloured foil square cake boards as reflectors for macro photography (for fill in with natural light). Then I just sandwich my diffusers between it for the flash as flat sheets. Then I can just put them in the outside of my camera bag pockets, and the rigidity of the cake boards stops them getting bent or creased.




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Archibald
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Apr 28, 2016 14:42 |  #39

Spring has arrived here in our area, and I am trying out the paper diffuser with the 270EX flash. The light quality and quantity seem to be good, but sharpness seems to be off a bit. Not quite sure what the issue is, whether it's focus error or camera movement or what. Examples below.

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Lester ­ Wareham
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Apr 29, 2016 00:15 |  #40

Nice and diffuse, perhaps too much, could the perceived lack of sharpness be due to the light being too flat?

I guess more loss on the flash will mean a longer flash but the effective exposure time should still be very short; was there a lot of ambient light that might contribute to the exposure?


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Archibald
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Apr 29, 2016 01:24 |  #41

Lester Wareham wrote in post #17988985 (external link)
Nice and diffuse, perhaps too much, could the perceived lack of sharpness be due to the light being too flat?

I guess more loss on the flash will mean a longer flash but the effective exposure time should still be very short; was there a lot of ambient light that might contribute to the exposure?

Thanks for the comments, Lester.

Maybe the flash exposure duration is long enough to allow movement to show. I will try some experiments to find out.

I don't know about you, but shots of bugs inevitably get me into strange off-balance positions, so the camera might not have been very steady.

There was sunlight in some of the shots (not shown) taken during this session. Those shots all clearly showed well defined shadows. The posted ones don't, so the ambient light was overcast or in my shadow, and must have been a couple stops below the flash exposure. Might be worth checking some more too.


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Dalantech
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Post has been edited over 1 year ago by Dalantech.
Apr 29, 2016 03:35 |  #42

Archibald wrote in post #17989020 (external link)
...There was sunlight in some of the shots (not shown) taken during this session. Those shots all clearly showed well defined shadows. The posted ones don't, so the ambient light was overcast or in my shadow, and must have been a couple stops below the flash exposure. Might be worth checking some more too.

One trick is to try is setting the flash to second (or rear) curtain sync so that if the sensor is recording some ambient light then the flash will be the last significant light source. You'll still get motion, but the detail will still be there. Early last year I was experimenting with natural light and flash and was trying to find a good balance between getting enough natural light to expose the background and use the flash to expose the subject. Kept running into situations where I was too close to the natural light exposure, but second curtain sync allowed me to get some detail anyway. The motion ends up looking like a shadow, and there was over two meters between the subject and the sidewalk in the background. Notice the hard lines around the flower, proboscis, and the antenna at the top (Tech Specs: Canon 70D (F11, 1/30, ISO 200) + a Canon EF-S 60mm macro lens with 37mm of extension):

IMAGE: https://farm6.staticflickr.com/5698/20688023059_deab449b9d_c.jpg
[IMAGE'S LINK: https://flic.kr/p/xw8w​uK] (external link)Bumblebee in Lavender III (external link) by John Kimbler (external link), on Flickr

The 1/focal length rule for hand holding a camera breaks down as you approach life size, and practically doubles at 1x (and just keeps getting worse as the mag goes up). With a 60mm lens, and the sensor picking up some natural light, I don't like shooting below 1/125 of a second at 1x.

Typically really good diffusion will not cause a decrease in detail, in fact just the opposite since there is some fine textures that can be blown out by strong microcontrast (caused by the light not being diffused enough). The better the diffusion is the more you can push the sharpening in post without making a shot look over sharpened.

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A-PeeR
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Apr 29, 2016 07:25 |  #43

Archibald wrote in post #17989020 (external link)
Maybe the flash exposure duration is long enough to allow movement to show. I will try some experiments to find out.

I don't know about you, but shots of bugs inevitably get me into strange off-balance positions, so the camera might not have been very steady.

I wondered about the flash pulse duration. Curious, how do you know what output level you are using with the 270EX? Do you control the output level by FEC applied in camera or is there some other way to do this? Please excuse my ignorance but I use the 430EXII or the 600EX-RT and manually dial in flash output on the unit.




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SteB
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Apr 29, 2016 08:51 as a reply to Archibald's post |  #44

Without seeing the original images I can't say what the issue is. However, with my concave diffusion principles the image often comes out very low contrast out of camera, and can initially seem soft. I created a diffuser to produce this very low contrast lighting so I could use strong sharpening and microcontrast boosts in post-processing without it looking over-sharpened. This was to counteract the diffraction softening of using quite a small effective aperture. At 1:1 an nominal aperture of f11 i.e. the aperture shown on Canon DSLRs is actually an effective aperture of around f22, and well into the zone where diffraction softens the image.

Undiffused or less effectively diffused macro flash creates a type of natural sharpening. What I mean by this is that you get little bright bits with blown highlights, and deep black shadows. This gives high acutance i.e. apparent sharpness. In luminance values the white is close to 255 and the black close to 0. The problem with this if it's in your RAW file it's baked in. What's more if you try to apply more sharpening or microcontrast to counteract diffraction softening it will look horribly over-sharpened. This is the reason for using low contrast lighting. With what videographers call grading you can add contrast and processing to a low contrast image. Unfortunately you cannot undo high contrast in an image when the contrast is baked into your original exposure. It's the same for overall image and microcontrast. It is far easier to work on a low contrast image in post-processing, and then to finally adjust the contrast to taste.

What I'm saying is that with no flash diffusion for macro flash, or less effective diffusion that it looks sharper out of camera, but you can't do much with the image in post processing without it looking over-sharpened. Whilst these images look sharp at web size if you look at them at 100% view, they are lacking in image detail. By using low contrast but oblique lighting, and then additional sharpening and microcontrast boost in post processing, there is far more apparent detail at 100% view. Before applying this extra sharpening and contrast boost I use noise reduction software (Topaz DeNoise) to remove any image noise (this will act like a key for the sharpening and will create ugly sharpening artifacts.

There's a difference between low contrast oblique light and flat lighting, even if they look superficially similar before post-processing.

Flat lighting is lighting from the front. Here there are no shadows at all, and if there are small bumps i.e. texture, there is no highlight on one side, and a shadow below as you get in oblique lighting which brings out the texture in a photograph. Even increasing sharpening, microcontrast, and overall contrast will not re-create texture with flat frontal lighting.

However, with low contrast oblique lighting from say above, there are still micro shadows below texture and brighter highlights above, it's just that they're not visible yet in an unprocessed image. When you increase sharpening and micro contrast, with say wide pixel radius sharpening, along overall contrast boosts, this texture will become far more apparent.

It's easiest to illustrate it with this image, which I used to counteract mistaken criticisms that the lighting from my diffusion was flat. These are the same exposure of the same Ladybird taken with my concave diffusion. The image on the left has had a moderate amount of sharpening and boosting of the micro contrast, and overall contrast. The image on the right has had more sharpening, microcontrast boost, and overall contrast adjustments. Not how much more image detail is apparent, and notice how it has brought out far more of the texture of the subject, which would not have been possible if this was truly flat lighting.

IMAGE: https://farm5.staticflickr.com/4058/4544922993_f696be74a8_b.jpg
[IMAGE'S LINK: https://flic.kr/p/7VBV​gg] (external link)Sharpening comparison (external link) by Stephen Barlow (external link), on Flickr

What I cannot say without looking from a full resolution image or a crop from the out of camera exposure is if the images are soft i.e. the detail is blurred, low resolution, whether the image has flat shadowless lighting, or if the light is just low contrast (where better processing would bring out more detail). As I think I said earlier I have tried bond paper as a diffuser. However, I found it absorbed far too much light, so it is possible your flash is firing at nearly full power and not freezing motion. There is a way to test this. Whilst the 270EX does not have manual power ratios on the flash, with many Canon DSLRs you can go into the menu and find the external flash control panel. This allows you to adjust the power ratio in manual, so you can establish what power level your flash if firing at for a correct exposure i.e. if it is firing near full power.

If the diffuser is simply absorbing too much light then simply use velum paper or preferably diffuser gel in it's place. Both are easy to cut, and all you have to do is to use your bond paper diffuser as a template, draw around it with a pencil and cut a diffuser out of one of these other materials. Both velum paper and diffuser gel transmit far more light than bond paper, but they still have excellent diffusion characteristics even with a single thickness. Having said this, if your flash is firing straight through the diffuser at the subject, you might get a bright spot. So possibly you could just a double thickness with a gap, or just a double thickness where the centre of flash strikes the diffuser.



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Lester ­ Wareham
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Apr 29, 2016 12:06 |  #45

Archibald wrote in post #17989020 (external link)
Thanks for the comments, Lester.

Maybe the flash exposure duration is long enough to allow movement to show. I will try some experiments to find out.

I don't know about you, but shots of bugs inevitably get me into strange off-balance positions, so the camera might not have been very steady.

There was sunlight in some of the shots (not shown) taken during this session. Those shots all clearly showed well defined shadows. The posted ones don't, so the ambient light was overcast or in my shadow, and must have been a couple stops below the flash exposure. Might be worth checking some more too.

In highlight above. Oh yeh, its a bit like isometric exercise, I get hot fast when staying very still snapping away. My better half is often standing around with me complaining of being cold (she's always cold!).


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