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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

 
Archibald
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Apr 30, 2016 16:06 |  #61

Dalantech wrote in post #17990815 (external link)
LOL! It's obviously too late in my day :)

When you pull the flash head out it actually concentrates the light. My bad. I though it would work to help force the light to spread out. Doh!

Agreed.


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Wilt
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Apr 30, 2016 18:05 |  #62

Not usually being inclined to macro photography as a pastime pursuit, I had not dealt significantly with the issue of lighting tiny things, nor the characteristics of different types of light modifier shapes.

  • Since someone mentioned liking the 'wrap' of light from a concave surface diffusion panel, I decided to give that a try.
  • Also, in view of the size of the usual macro subject, anything 7" in size from 7" away is truly a 'large source', so would an even larger source do anthing to improve the lighting?!



Here is my test setup, showing a concave surface (left) and a convex surface (right). The plastic material is a translucent piece of polyethylene plastic normally used as a cutting surface in the kitchen, curved by using two pieces of string to pull it into a curve. While the ideal test would have had the luminous surface at a constant distance to the subject (a small handheld remote), the macro subject's placement had to keep the curved luminous surface away from the field of view of the lens...one might say I was dealing with a real world type of situation in which lighting modifiers can't always be located at the position we desire!

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/Principles/macro%20diffusion%20test_zpsxxteo8be.jpg

In addtion to these two 'sources' I also shot with the flash with native lens, and the same flash with a 5" x 7" Wescott MicroApollo softbox. In all cases, I wanted a low angle to the subject, to cast shadows from the buttons as well as from the remote control's case. The flash unit was always positioned with its hotfoot positioned at a small piece of masking tape for consistency of flash position and set on the tabletop.
Flash was on manual, I flash metered with the Minolta Autometer Vf, I shot at ISO 100, 1/200 f/16, adjusting the flash manual power for a constant aperture size on the lens.
Repro ratio is 0.3x lifesize (button '4' is 7mm across)

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/Principles/Macro%20diffusion_zpsb33dqti4.jpg

Shot 1 is with the 5" x 7" Wescott MicroApollo at 7" from the subject. Shot 2 is the flash head alone.
Shot 3 is with the convex curved polyethelene. Shot 4 is with the concave curved polyethelene, and the frontal area is 12" x 17", about 2.5x the Wescott in apparent size

Comparing shot 1 vs. shots 3 or 4, I do not see a significant difference in softness due to increased apparent size of the source. Part of that is simply the inability to move the flash head away from the translucent polyethylene sheet so as to fill the entire surface area.
As for comparing shot 3 vs. shot 4, I would say the concave is a bit harsher, and again I would blame the fact that the flash head is so much closer to the surface so the spread of light across it is more limited than with the convex surface.

Another test, this next time with concave and convex both
  • at same distance to subject AND
  • with flash head to plastic surface at same distances to each other,


are in order. Based upon these initial test results, I would not bother carrying around a rolled up piece of polyethylene for its size, the 5x7" softbox does just as well and is easier to deal with in the field. Even if the additional testing discloses that increased flash-to-polyethene gives better results, and that concave is superior to convex, it may still be too much bother for field work, and might be better reserved for the pace and control of studio conditions.

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Archibald
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Apr 30, 2016 18:14 |  #63

Wilt wrote in post #17990928 (external link)
Not usually being inclined to macro photography as a pastime pursuit, I had not dealt significantly with the issue of lighting tiny things, nor the characteristics of different types of light modifier shapes.
...

...

Very good, Wilt. Note that convex sheets are concave too, on the other side. When you say convex, do you mean wrapping around the subject or wrapping around the light?

And yes, it is essential that the flash output cover the entire sheet.


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Wilt
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Apr 30, 2016 18:21 |  #64

Archibald wrote in post #17990933 (external link)
Very good, Wilt. Note that convex sheets are concave too, on the other side. When you say convex, do you mean wrapping around the subject or wrapping around the light?

And yes, it is essential that the flash output cover the entire sheet.

I am using the definition that a dome is a convex shape shielding us from the rain, a bowl is a concave shape the holds the soup.

In going back to my earlier post, I had inadvertantly flipped flopped the terms in places, which are now corrected in post 62


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Wilt
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Apr 30, 2016 19:16 |  #65

OK, here is the followup test. This time, for both shots, the surface of the curved piece of polyethylene was fixed at 10" to the subject, the flash was fixed at 10" away from the surface of the polyethylene with flash set at 24mm coverage angle.

The concave result...

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/Principles/Concave_zpscmhahbk4.jpg

The convex result....

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/Principles/Convex_zpsftjrpio7.jpg

The convex setup looked like this...

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/Principles/Convex%20setup_zpssmg3fmke.jpg
, the front of the flash would be at the 20" mark on the ruler (not close to the camera) during actual shots taken.

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Archibald
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Apr 30, 2016 20:13 as a reply to Wilt's post |  #66

Wilt,

I will let SteB deal with the ins and outs of concave diffusers.

My diffuser assumed a concave shape because it worked with the shape of the lens, and because the shape gave it some structural stability. IMO the concave shape might improve the quality of the lighting, but I doubt by much.

BTW, I don't think anyone advocates a convex shape for a light modifier.


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Wilt
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Apr 30, 2016 23:27 |  #67

Archibald wrote in post #17991044 (external link)
BTW, I don't think anyone advocates a convex shape for a light modifier.

The point that SteB had made was that concave was better, with the explanation about the light falloff from the edges to the subject. In testing the theory I simply wanted to try to exaggerate what might result from the convex modifier.

As we see vs. my somewhat small Wescott softbox, there is not a whole lot of difference between my softbox and the convex. And there does not seem to be a whole lot of visible difference vs. the concave either.

Folks sometimes refer to improved 'wrap' with umbrellas. Since the umbrella is purely a reflective surface there is an element of truth if the source is a bare tube pointed into the umbrella dish. And folks do also use translucent umbrellas as shoot-thru devices, and in this case they are convex shapes. Effectively what SteB advocated was what amounts to using a shoot-thru translucent umbrella with the umbrella shaft pointed toward the subject, for macro subjects. So my testing simply was analogous to pointing the shoot-thru umbrella shaft toward the subject vs. away from the subject.

I will not claim my testing was exhaustive, it was merely one diffusive material being tested, not unlike others trying vellum vs. bond. I provided another data point.


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Dalantech
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May 01, 2016 00:01 |  #68

Archibald wrote in post #17991044 (external link)
...I don't think anyone advocates a convex shape for a light modifier.

The only reason I use a convex diffuser (Gary Fong Puffer Plus) is because the surface is dimpled, so it acts like a much larger diffusion surface. If I could find a flat material with the same characteristics I'd use it.


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Dalantech
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May 01, 2016 00:06 |  #69

Wilt wrote in post #17991215 (external link)
The point that SteB had made was that concave was better, with the explanation about the light falloff from the edges to the subject. In testing the theory I simply wanted to try to exaggerate what might result from the convex modifier.

I'm not gonna say that one shape is necessarily better than the other, but in your tests the convex is diffusing the light better (look at the shadows).

It seems to me that a concave shape would act like a concentrator for the light, and to me that's counterintuitive to diffusion.


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Archibald
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May 01, 2016 01:08 |  #70

Dalantech wrote in post #17991238 (external link)
The only reason I use a convex diffuser (Gary Fong Puffer Plus) is because the surface is dimpled, so it acts like a much larger diffusion surface. If I could find a flat material with the same characteristics I'd use it.

Well, that is convex - but at non-macro distances, I don't think the shape of the diffuser matters.


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LordV
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May 01, 2016 01:11 |  #71

Interesting discussion. I have a feeling that the shape of the diffuser does not really matter that much, what matters is the apparent size of the diffuser from the subjects POV and from that I think it's possible to get more diffusing area near the subject with a concave shape - ie it wraps around the subject.
With dead subjects the favourite diffuser is a hemisphere which is placed over the subject with a hole in it for the lens to see the subject.
Of course practicality comes into this a bit when shooting in the field. I found any protruding type diffuser either scares away the subject more than normal or stops me getting the lens into the position I want, but I guess we all get used to the limitations of the system we are using and like many things in macro photography the end result is a compromise between competing factors.

Brian v.


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Dalantech
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May 01, 2016 02:04 |  #72

LordV wrote in post #17991319 (external link)
Interesting discussion. I have a feeling that the shape of the diffuser does not really matter that much, what matters is the apparent size of the diffuser from the subjects POV and from that I think it's possible to get more diffusing area near the subject with a convex shape.
With dead subjects the favourite diffuser is a hemisphere which is placed over the subject with a hole in it for the lens to see the subject.
Of course practicality comes into this a bit when shooting in the field. I found any protruding type diffuser either scares away the subject more than normal or stops me getting the lens into the position I want, but I guess we all get used to the limitations of the system we are using and like many things in macro photography the end result is a compromise between competing factors.

Brian v.

Agreed -it really just boils down to apparent light size. Just about everything that I do with my light is dictated by my personal style of shooting and how I want the final image to look.


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Dalantech
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May 01, 2016 03:14 |  #73

Archibald wrote in post #17991314 (external link)
Well, that is convex - but at non-macro distances, I don't think the shape of the diffuser matters.

True. Again I use it not because it's convex, but because the surface is "dimpled" so it acts like a much larger diffuser. Video if you're interested (external link).


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Wilt
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May 01, 2016 09:20 |  #74

LordV wrote in post #17991319 (external link)
Interesting discussion. I have a feeling that the shape of the diffuser does not really matter that much, what matters is the apparent size of the diffuser from the subjects POV and from that I think it's possible to get more diffusing area near the subject with a concave shape - ie it wraps around the subject.

...Of course practicality comes into this a bit when shooting in the field. I found any protruding type diffuser either scares away the subject more than normal or stops me getting the lens into the position I want, but I guess we all get used to the limitations of the system we are using and like many things in macro photography the end result is a compromise between competing factors.


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.


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May 01, 2016 09:24 |  #75

Dalantech wrote in post #17991378 (external link)
True. Again I use it not because it's convex, but because the surface is "dimpled" so it acts like a much larger diffuser. Video if you're interested (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!


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