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FORUMS Photography Talk by Genre Macro Talk
Thread started 16 Jan 2016 (Saturday) 18:57
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Bond paper diffuser

 
SteB
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May 01, 2016 12:12 as a reply to post 17990928 |  #76

You have completely misunderstood the way a concave diffuser should be used for macro photography. As I originally designed both types of concave diffuser, and coined the term "concave diffuser" with regard to macro photography, I think I am best qualified to describe it.

The outline of both these principles is described here with diagrams. Please note the the end of lens concave diffuser is described in the diagrams as a "cup diffuser" because the first one I made an use was made from a plastic cup.
https://www.flickr.com .../albums/72157623486​703625 (external link)

First of all the light source is supposed to come from directly over above subject. Likewise the end of lens concave diffuser is meant to go right around the subject at a close distance to it. In other words, the top of diffuser and the sides of it are supposed to be the same distance from the subject. It is designed to work in the true macro range. None of your set-up conforms to this at all. What is more on your set up, the flash is much closer to the centre of the diffuser when it is bent into a concave shape, than a convex shape. This completely distorts the results as the area of the diffuser being illuminated by the flash is much greater on the convex shape, than on the concave shape. In addition you have not curved the concave diffuser so it wraps around the subject.

If you want to genuinely test a concave diffuser as I designed and described it with this type of set up, your diffuser would be bent into a true half cylinder, and it would go over the top of the subject, with the flash above and firing down to it. Unfortunately the very detailed articles/threads where I first described how and why these principles work, on Juza Nature are no longer on the internet, as that version of the website no longer exists. However, this method has now been used all over the world by many macro photographers such as Orionmystery (Kurt) who have proved beyond doubt that this method works. This is the major thing. It has been proved by many photographers to work, and give the lighting most free of specular reflections on shiny invertebrates.
http://orionmystery.bl​ogspot.co.uk/ (external link)

A discussion of the effectiveness of this method of concave diffusion can be seen on this Photography on the Net thread.
http://photography-on-the.net .../showthread.php?t=1​324499

The method of concave diffusion with macro photography is for reducing specular reflections on the curved shiny surfaces of invertebrates. It is design to work at macro distances, where the diffuser is only a few centimetres from the surface. This is especially important for understand how and why this works. Lighting in the macro region is different than at longer relative distances. As I say, if you set up the diffuser as I designed it to be used, and use a curved shiny surface, you will see how effective it is. Plenty of others have already carried out these tests. The light source should be above the subject, in front of it to a degree, and pointing down, but not directly over the subject.




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SteB
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May 01, 2016 12:17 |  #77

Wilt wrote in post #17991615 (external link)
While I had thought that the concave shape could help, on the testing done so far there does not seem to be a large difference which is evident. I am remaining open minded on the topic, pending some more tests, but initial results don't bear this out.

In conducting the tests so far, I did indeed get an initial impression about large curved reflectors as interering with lens placement, and subject skittishness also seemed to be an obvious consideration. Given the small apparent difference vs. a small softbox mounted on the flash head, again the first outcome seems to point in 'not worth bothering' in the field.

The reason it doesn't appear to work is:

a) That you are not using the concave diffuser over the top of the subject, and the light source from above an in front.

b) It is not being used on a proper macro sized subject, with the diffuser at the distance it is supposed to be used.




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Wilt
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May 01, 2016 12:34 |  #78

Thx for beginning to clarify what you meant in your previous posts about the use of Concave modifiers. The fact that the lighting is overhead, above the subject and not frontal...is it at a 45 degree angle downward, or like a canopy over the subject?

Thanks also for making it clear about eliminating specular reflections from surfaces of the subject, rather than for the purposes of 'wrapping' illumination around a 3D object for better illumination. Having the explicit purposes of this stated clearly helps me to understand...it is not unlike product photography, merely on a much smaller scale!


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SteB
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May 01, 2016 13:06 |  #79

Wilt wrote in post #17991900 (external link)
Thx for beginning to clarify what you meant in your previous posts about the use of Concave modifiers. The fact that the lighting is overhead, above the subject and not frontal...is it at a 45 degree angle downward, or like a canopy over the subject?

Thanks also for making it clear about eliminating specular reflections from surfaces of the subject, rather than for the purposes of 'wrapping' illumination around a 3D object for better illumination. Having the explicit purposes of this stated clearly helps me to understand...it is not unlike product photography, merely on a much smaller scale!

Yes, that is it exactly. I was looking to replicate the type of light you can get in a product photography light tent, but in a very small portable set up which could be used in the field. It has it's downsides in that it is more difficult to place over a live subject without it flying or running off. The idea is that the shadows, which are light fall under the subject. In fact the flower or the ground the subject is on, act a bit like a secondary reflector firing light back up into the diffuser which acts like a reflector. This is one of the differences with your set up. There was not much light being reflected up, into the diffuser, and reflected back down. As you are aware a translucent or semi-opaque material does not just transmit strong light, but reflects a lot of it down. With my original cup diffuser light was bounced around in side it.

It is very much like photographing a piece of jewellery. Originally I tried using Alex Wild's tracing paper type diffuser, but with material cut from plastic computer dust covers. It worked well, but was difficult to use in vegetation as the wide design of the diffuser caught the vegetation. So I wanted something more compact I could push into small gaps in the vegetation, and that was where the cup diffuser came in. The following year I decided to work out why it worked so well. I came up with another type of concave diffuser, an inverted dome in a reflective tube, which actually re-shapes and focuses the light, but it's beyond the subject being discussed here.

I have been trying out these cone shaped end of lens diffusers for a few years. The idea is that they are a compromise, which allows more room above the subject.




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SteB
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May 01, 2016 13:14 as a reply to post 17990072 |  #80

Yes I thought it might not soften the light as much. As I say I have tried bond paper, and whilst it gave very soft light it absorbed to much light. The reason the vellum paper is less effective is that there is a bright spot on it from where the flash hits it. You can counteract this in a few ways. With my own very similar set up using the 270EX I have a small bit of light diffuser gel bent into a right angled shape. This attaches just under the flash head with self-adhesive velcro. The bent up end is about 1 1/2 inches in front of the flash head, and this sort of pre-softens and spreads the light a bit more so there is more scatter before it hits the diffuser. You could also stick a second small patch of vellum paper on where the flash hits the centre of the diffuser. I would also suggest putting a simply reflective bounce card over the top of the flash. This will concentrate more of the light onto the flash, including lighting the sides and lower part of the diffuser. It might increase the light efficiency a bit.




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Archibald
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May 01, 2016 13:51 |  #81

SteB wrote in post #17991948 (external link)
Yes I thought it might not soften the light as much. As I say I have tried bond paper, and whilst it gave very soft light it absorbed to much light. The reason the vellum paper is less effective is that there is a bright spot on it from where the flash hits it. You can counteract this in a few ways. With my own very similar set up using the 270EX I have a small bit of light diffuser gel bent into a right angled shape. This attaches just under the flash head with self-adhesive velcro. The bent up end is about 1 1/2 inches in front of the flash head, and this sort of pre-softens and spreads the light a bit more so there is more scatter before it hits the diffuser. You could also stick a second small patch of vellum paper on where the flash hits the centre of the diffuser. I would also suggest putting a simply reflective bounce card over the top of the flash. This will concentrate more of the light onto the flash, including lighting the sides and lower part of the diffuser. It might increase the light efficiency a bit.

I might do some experiments with the vellum. Adding more at strategic places will probably help, but will reduce the brightness of the light, bringing it closer to the bond paper diffuser. Maybe there is an optimum density there somewhere.

As I suggested earlier in this thread, nothing done at the face of the flash will affect the softness of the light at the subject, provided the diffuser is evenly illuminated by the flash. Adding a diffuser on the face of the flash only wastes light by scattering it to the side.

Adding something to the flash that could reduce the intensity in the center of the diffuser and redistribute it more to the sides would help - maybe some kind of magic lens.

Or maybe we can regard the hot spot as an advantage, as it gives more shape to the subject.


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Dalantech
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Post has been last edited over 1 year ago by Dalantech. 2 edits done in total.
May 01, 2016 13:52 |  #82

Wilt wrote in post #17991620 (external link)
Your video links don't do anything (not even a badly resolved link)...no action at all.

Could you find a non-dimpled modifier which is otherwise similar to what you do use, and shoot same subject with both and post results?

The apparent size -- my 5x7" softbox vs. the 12x17" size -- on a macro subject certainly does not seem to matter, and I speculate that the 7" size is already quite large compared to the macro subject, so that even larger size does not result in that much more apparent softness at the subject!

Try this one (external link) -odd that the other link doesn't work.

I think it would depend on how close the diffuser is to the subject in both cases. I don't have room at the end of the lens for a 5x7" diffuser. I have tried other materials for that final stage and none perform as well as the Puffer Plus's do.

Edit to say that I think Strobist mentioned that you can hit a point with diffusion where you have to effectively double the size of the diffuser, relative to the subject, to make any substantial difference in diffusion. Can't find a link to the comment, but it's the reason why my current diffuser is actually smaller than what I use to use. Making a bigger one doesn't seem to make enough of a difference and dealing with a bigger diffuser at the end of the lens just makes it more difficult use.


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Dalantech
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Post has been edited over 1 year ago by Dalantech.
May 01, 2016 14:00 |  #83

Archibald wrote in post #17991993 (external link)
...As I suggested earlier in this thread, nothing done at the face of the flash will affect the softness of the light at the subject, provided the diffuser is evenly illuminated by the flash. Adding a diffuser on the face of the flash only wastes light by scattering it to the side.

...Adding something to the flash that could reduce the intensity in the center of the diffuser and redistribute it more to the sides would help - maybe some kind of magic lens....

Those two statements seem to counter each other...

I bought a wide angle diffusion panel for the 600RT, cut it in half, and hot glued it directly to the MT-24EX's flash heads. It forces the light to spread out in a way that does reduce the hot spot in the middle of my specular highlights. Any light that is directed out the sides of the flash is simply bounced out toward the end of the diffuser with a reflector. So I get a mix of direct diffused and bounced diffused light (although most of the light coming out of the diffuser is direct diffused). I took this shot yesterday with the MP-E 65mm at 1x (maybe a little off of the 1x mark on the lens, but not much) so it's pretty much a worse case example because I'm at the greatest distance between the diffuser and the subject. I didn't do anything special in post -the shot is the result of the light quality that I'm getting:

IMAGE: https://farm2.staticflickr.com/1629/26142963043_19a4465e52_c.jpg
[IMAGE'S LINK: https://flic.kr/p/FQaw​78] (external link)Feeding Honeybee (external link) by John Kimbler (external link), on Flickr

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Archibald
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May 01, 2016 14:05 |  #84

Dalantech wrote in post #17992005 (external link)
Those two statements seem to counter each other...

I bought a wide angle diffusion panel for the 600RT, cut it in half, and hot glued it directly to the MT-24EX's flash heads. It forces the light to spread out in a way that does reduce the hot spot in the middle of my specular highlights. Any light that is directed out the sides of the flash is simply bounced out toward the end f the diffuser with a reflector. So I get a mix of direct diffused and bounce diffused light (although most of the light coming out of the diffuser is direct diffused). I took this shot yesterday with the MP-E 65mm at 1x (maybe a little off of the 1x mark on the lens, but not much) so it's pretty much a worse case example because I'm at the greatest distance between the diffuser and the subject. I didn't do anything special in post -the shot is the result of the light quality that I'm getting:

My premise is even illumination of the diffuser. It doesn't matter how it gets evenly illuminated. The softness will be the same.

I should add: softness will be the same with even illumination and same light direction.


Hasselblad 500 C/M with 80mm/2.8 Zeiss Planar (trying to sell it); Pentax Spotmatic F with 28/3.5, 50/1.4, 50/1.8, 135/3.5; Canon digital gear
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Dalantech
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May 01, 2016 14:07 |  #85

Archibald wrote in post #17992009 (external link)
My premise is even illumination of the diffuser. It doesn't matter how it gets evenly illuminated. The softness will be the same.

OK :)


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SteB
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May 01, 2016 17:12 |  #86

Archibald wrote in post #17991993 (external link)
I might do some experiments with the vellum. Adding more at strategic places will probably help, but will reduce the brightness of the light, bringing it closer to the bond paper diffuser. Maybe there is an optimum density there somewhere.

As I suggested earlier in this thread, nothing done at the face of the flash will affect the softness of the light at the subject, provided the diffuser is evenly illuminated by the flash. Adding a diffuser on the face of the flash only wastes light by scattering it to the side.

Adding something to the flash that could reduce the intensity in the center of the diffuser and redistribute it more to the sides would help - maybe some kind of magic lens.

Or maybe we can regard the hot spot as an advantage, as it gives more shape to the subject.

At this distance the flash does not illuminate the whole diffuser, and the light is concentrated on the central part. The idea of pre-diffusing the flash is to spread out the light more before it hits the diffuser, so it's more evenly distributed over the diffuser, rather than being a bright central part.

To understand how the flash works I either shine a powerful LED light through it, or I fire the flash on low power with the lights dimmed, and you can see the pattern. Sometimes I take a photo of the diffuser being lit up by the flash to see how easily distributed the light is across the diffuser.

I regard this type of cone shaped of flared diffuser as a compromise for when the best diffusion isn't required. In fact I often just use it for fill-in on predominantly natural light exposures. The flared shape makes it more versatile as it is less likely to shade or scare more skittish insects, where it can be difficult to put a none flared end of lens concave diffuser over the subject.




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Wilt
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May 01, 2016 17:12 |  #87

Dalantech wrote in post #17991994 (external link)
Try this one (external link) -odd that the other link doesn't work.

I figured out that I was clicking the wrong thing...I had tried moving the mouse on top of the blue double-arrow; I now know the right place to click was actually on the text "Video if you're interested". It would be good if you could format "Video if you're interested" or "Try this one" as underlined blue text, so the text visually looks like a web link, for example, since POTN doesn't do that automatically.


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Archibald
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May 01, 2016 17:53 |  #88

SteB wrote in post #17992215 (external link)
At this distance the flash does not illuminate the whole diffuser, and the light is concentrated on the central part. The idea of pre-diffusing the flash is to spread out the light more before it hits the diffuser, so it's more evenly distributed over the diffuser, rather than being a bright central part.

To understand how the flash works I either shine a powerful LED light through it, or I fire the flash on low power with the lights dimmed, and you can see the pattern. Sometimes I take a photo of the diffuser being lit up by the flash to see how easily distributed the light is across the diffuser.

I regard this type of cone shaped of flared diffuser as a compromise for when the best diffusion isn't required. In fact I often just use it for fill-in on predominantly natural light exposures. The flared shape makes it more versatile as it is less likely to shade or scare more skittish insects, where it can be difficult to put a none flared end of lens concave diffuser over the subject.

My fan-shaped diffuser (which is 22 cm wide) subtends an angle of about 60 degrees at the flash head. The 270EX II in normal mode is suitable for a 28mm lens on FF, which corresponds to about 66 deg. So I'm fully covered. Any additional diffuser on the flash head won't help but will just dim the light.

Yes, I agree it is a compromise.


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May 01, 2016 18:26 |  #89

Aphid eating my rose bush.

Taken with the 100mm L with 68mm of extension tubes, which I think is about 1.7x. Cropped about 50% linear, so effectively 3.4x. Hand-held. 270EX II flash at 1/16 power and bond paper fan-shaped diffuser on the front of the lens.

A bit soft on the eyes. That is focus error. This was the best out of several.

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Archibald
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May 02, 2016 18:40 |  #90

I've been shooting a bit with the fan-shaped diffusers. The bond paper works well, and so does the vellum. Here's a comparison of the two. For the vellum shot, I took the flash power down about two stops. To me, the two look almost identical. Other shots show that the vellum gives more contrasty light, but it is not bad at all.

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