LSD for macro photographers (high-tech diffusion material)

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Bob^3
Posts: 287
Joined: Sun Jan 17, 2010 1:12 pm
Location: Orange County, California

LSD for macro photographers (high-tech diffusion material)

Post by Bob^3 »

No, this is not a way to create “psychedelic” macro images through ingestion of psychoactive chemicals (although that also might be an interesting test)! :D

LSD (Light Shaping Diffusers) is one of several trade names for a special class of high-tech diffusion materials that incorporate a unique randomized pattern of microlenses or “microlenslets” (with different focal lengths) formed into the surface of plastic sheet material or coatings on glass. Other trade names include “Engineered Diffusers” or the general name “microlens diffusers” all of which fall under the broader category of “holographic diffusers”.
For reference, here are two earlier threads which refer to this or similar materials:

http://www.photomacrography.net/forum/v ... 2fdd928d0b

http://www.photomacrography.net/forum/v ... php?t=8783

Although the properties of Edmund Scientific's holographic diffusers mentioned in the first thread appear to be the same as microlens diffusers like LSD, they are relatively expensive and small in size. So apparently no members have been willing to buy one to test (?).

http://www.edmundoptics.com/onlinecatal ... &PageNum=3

These threads touched a memory of an article I read in a Photonics or SPIE publication, from at least several years ago, about the ongoing development of such materials for mass production (at low cost). The intended applications were in high efficiency LCD backlights (BLUs) to be used in computer monitors, TVs and cell phones as well as shaped light sources for machine inspection systems. I believe these diffusers have a high potential for macro photography lighting. So I’ve been doing some research for the past several weeks. Given the many ongoing discussions regarding diffusers on this forum, I thought I’d share what I’ve found so far, including some less expensive sources for larger sheets of the material.

The key patents appear to be held by two companies, Physical Optics Corp. (POC) (with their spin-off company, Luminit, LLC) and RPC Photonics:

http://www.poc.com/lsd/default.asp?page ... ripwithlsd

http://www.luminitco.com/

Properties and applications:

http://www.luminitco.com/Light_Shaping_Diffusers_LSD

http://www.luminitco.com/How_They_Work

http://www.rpcphotonics.com/engineered.asp

Some more technical descriptions:

http://www.physics.uci.edu/~isis/Yountville/Sales.pdf

http://www.rpcphotonics.com/pdfs/RPC_Lu ... tation.pdf

The properties which I think might prove valuable in macro lighting are:

1. very good “homogenization” of incoming light

2. high efficiency, 85% to 92% transmission (other roughened “surface” diffusers like ground glass show about 65% transmission, “volumetric” diffusers like opal glass, show about 20% to 40% transmission, ping pong balls? :D ).

3. able to shape an incoming (collimated) beam into a wide variety of specified divergence angles---so offer potentially more light on the subject.

4. can project an evenly illuminated spot (round, oval, square, etc) across a surface, unlike other surface diffusers like ground glass that produce a Gaussian beam profile.

5. maintains polarization of the incoming beam.

Sources of diffusion sheets:
A free sample of LSD sheet is available directly from Luminit. It consists of 9 individual, 1.5” x 1.7” (38mm x 43mm) samples at various divergence angles formed into an 8 x 10 inch sheet of thin polycarbonate film. They do seem to require a company name to ship to and a carrier (UPS, FedEx) account number to cover shipping charges. They also have larger sample sheets available for $49 each, including full single angle 8 x 10 inch sheets of any standard angle and a larger “variety” sheet containing 7 angle types, each 2 x 22 inch in size (don't think they list these prices or details on their site).

An eBay search turned up this inexpensive diffusion sheet intended for LED lighting from a vendor in the UK:

http://cgi.ebay.com/Microlens-sheet-LED ... 27b5719acc

I purchased a number of these at the four divergence angles offered and they do appear to be microlens diffusers. However, they are designed to shape the beam into an elongated oval shape or line pattern. But two can be used with crossed planes to form a circular pattern with about 10% extra (20% total) light loss. Also, I think the appropriate Luminit material may be a better match for some macro lighting applications, with better known specifications.

I’ve disassembled a number of non-working LCD displays and panels to see what type of diffusers they use. These “for parts or repair only” units seem to go for $10 to >$100 on eBay, plus shipping---even the ones with smashed glass!? But a cheap source of damaged (cracked glass) LCD panels from monitors and TVs is your local electronic salvage yard. I know a guy at a large yard near me. When I called him he said he had stacks of LCD panels that they would have to pay to dispose of because of the few mg of Mercury used in the CCFL lamps. He asked “how many tons do you want?”! :roll:

Another interesting material harvested from some of these panels is the highest-efficiency linear polarizing film I’ve ever seen. By high efficiency, I mean when I overlay two sheets of this stuff with the polarization planes crossed, I measured about 11 stops of light attenuation compared to when the planes were parallel! Also, there was very little color shift at maximum attenuation, unlike the blue tint and low attenuation that occurs with most other polarizing filters. I’ve read that the contrast ratio of LCD displays is directly dependant on the efficiency of the polarizing films used. Unfortunately, the film is usually applied to the glass LCD panel with contact adhesive. But I was able to carefully peel it off by lifting one corner and slowly rolling it off onto a dowel. Although the film it is not crystal clear, it should work well to polarize a macro light source to help cancel reflections from specular subjects. I think similar polarizing film must be used in Singh Ray’s Vari-ND, variable ND filter, which offers up to 8 stops of attenuation, with little color shift. Some of these may be "wire grid polarizers" that can have efficiencies of 100,000:1.

Be aware that, while most LCD panels do use diffusion sheets in the BLU (along with prism sheets that work differently, AKA 3M’s BEF ), not all panels use microlens diffusion sheets. In fact, none of the older desktop and laptop monitors I’ve opened have had them, probably because of cost. But I’ve read that manufacturing costs for these are decreasing. So many of the newer designed monitors (about 50% made over the past year) and almost all cell phones now use them. Also, the more expensive larger monitors and TVs are more likely use them for their higher efficiency (brightness) and energy savings. It can be difficult to determine whether or not a diffusion sheet uses microlens technology. I’ve found a good way to tell is to place them between crossed polarizers. Microlens diffusers may rotate the polarization angle but they do not cause it to completely depolarize, like simple diffusers do. Also, I think it’s possible that how well the microlens diffuser maintains the polarization of the incoming beam may be an indication of the quality of the microlens surface. Using this test, I found the LSD samples maintain very high polarization and do not rotate the plane. Also, a laser pointer is a good collimated light source to see the divergence angle and evenness of the beam exiting the diffuser. If the beam is constrained to a relatively tight, well defined cone, it’s probably a microlens diffuser. If the beam is spread into a Gaussian profile, it’s a simple diffuser.

I now have samples from each of the sources above and will be testing them as time permits. One quick test however shows that the Luminit LSD sheet does a great job of “randomizing” the light from the end of non-randomized fiber optics guides, with little loss of light. In addition to natural subjects (arthropods, etc.) for planned testing, I’ve collected some highly reflective, polished chrome ball bearings ranging in diameter from 1mm to 10mm; I think these may offer the ultimate stress test for a macro illumination and diffuser setup.

Thoughts? Anyone experimented with the stuff?
Bob in Orange County, CA

Rusty
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Location: Mosselbay South Africa

Post by Rusty »

Bob, I managed to obtain a new broken lcd panel that seems to contain both the micro lens surface diffuser sheet and the bef sheet
The diffuser will probably not be as good as the engineered ones in your post but i am going to try to build a light as in the attached drawing to see the result from the panel if it is not curved
Any suggestions welcome !
Image
Daniel

Bob^3
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Joined: Sun Jan 17, 2010 1:12 pm
Location: Orange County, California

Post by Bob^3 »

Rusty wrote:Bob, I managed to obtain a new broken lcd panel that seems to contain both the micro lens surface diffuser sheet and the bef sheet
I don’t know all the configurations used in these panels; but of the few I’ve opened that I’ve identified as containing what are likely microlens diffuser sheets, none have also had BEF sheets. One reference stated that microlens diffusers can combine the functions (light shaping and diffusion) of the simple diffuser/BEF configurations into one sheet, thus significantly increasing efficiency compared to the inevitable loss of light which occurs with each additional film layer.

I should have mentioned that since the primary benefit of microlens diffusers is higher transmission efficiency, its use becomes more important with weaker light sources and at smaller effective apertures/higher magnifications. You’ve demonstrated that you have an excess of light when coupling a flash tube to your LCD light guide (at least with your current lens, aperture and magnification)---so with this configuration, efficiency doesn’t appear to be an important factor. However, once you reach higher magnifications and start focus stacking, the extra efficiency can become critical even with flash to allow proper exposure of dark subjects, maintain fast recycle times for the flash unit and prevent overheating the flash.

Your polarized light plate looks good. Of course, this is closer to how these components were intended to be used. The same approach should work with your curved illuminator in the other thread.

I like your diagram showing how prism films work by directing light forward toward the liquid crystal assembly, while refracting off-axis light back to the rear reflector for “recycling”.
Bob in Orange County, CA

Rusty
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Location: Mosselbay South Africa

Post by Rusty »

Bob wrote:
......none have also had BEF sheets....
Bob, i may be wrongly assuming it is a Bev sheet (i have not seen an of the shelf one yet)
It is a thin sheet with a metallic sheen, reflective only from one side
Placed on top of a white sheet of paper under ambient light,the section where the sheet covers the paper appears to be more white than the bare paper ?
Daniel

Bob^3
Posts: 287
Joined: Sun Jan 17, 2010 1:12 pm
Location: Orange County, California

Post by Bob^3 »

Bob^3 wrote:I don’t know all the configurations used in these panels; but of the few I’ve opened that I’ve identified as containing what are likely microlens diffuser sheets, none have also had BEF sheets.
Daniel, re-reading that statement, I didn't say it very well. What I meant was that microlens diffusers do not seem to be as common as simple matte surface diffusers. And that when no BEF sheets (which are very commonly found) are present in a panel, it may be more likely that the diffusion sheet in that panel uses microlens technology, since microlens diffusers can do the job of both BEF and simple diffusion sheets. My original statement could be wrong; some panels might use BEF in combination with microlens diffusers.

The point being that the diffusion sheet in your new panel may not use microlenses. You can check this by placing the diffuser between two linear polarizing filters. If the diffuser passes polarized light (darkens as one of the filters is rotated), then it's probably uses microlenses.
Rusty wrote:It is a thin sheet with a metallic sheen, reflective only from one side
Placed on top of a white sheet of paper under ambient light,the section where the sheet covers the paper appears to be more white than the bare paper ?
These are likely BEF (prism sheets). I've found one or two of these in almost every panel I've opened.
Bob in Orange County, CA

Craig Gerard
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Location: Australia

Post by Craig Gerard »

Bob^3,

Thanks for info on LSD (Light Shaping Diffuser).

I emailed Luminit and received some info regarding the LSD, the Linear samples (for strip lighting fixtures) and the order form.

I would be interested to see what happens when a beam of light is shone through each of the nine LSD samples with consideration of possible application for macro.
Luminit Light Shaping Diffusers® homogenize light to eliminate hot spots and add precise angular control with a large selection of angles.
Light Shaping Diffuser (LSD)
40° Circular
Image
60°x10° Elliptical
Image


Craig
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

DQE
Posts: 1653
Joined: Tue Jul 08, 2008 1:33 pm
Location: near Portland, Maine, USA

Post by DQE »

This is really interesting material, to say the least. Thanks to all who are contributing and/or commenting!

My mostly qualitative way of thinking about diffuser properties for macro work is that there are two basic parameters to be considered. First, the diffuseness of the light upon exiting the diffuser - totally diffuse would mean the light is emitted uniformly into a hemisphere. Second, one must consider the size of the illuminated diffuser vs the size of the subject. Per my best but no doubt limited understanding, an illuminated diffuser that occupies a large percentage of the space surrounding the subject is better than one that does not provide this feature. I believe but do not know with much certainty that a large partially diffuse diffuser would perform better than a perfectly diffuse but much smaller diffuser. If anyone can provide a quantitative or even better supported qualitative discussion of size vs diffuseness, I would be greatly interested, and suspect others would also be very interested.

These novel materials seem very interesting and very promising.
-Phil

"Diffraction never sleeps"

Bob^3
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Location: Orange County, California

Post by Bob^3 »

Craig Gerard wrote:I emailed Luminit and received some info regarding the LSD, the Linear samples (for strip lighting fixtures) and the order form.
Craig,

Do you mean you have received the 7-strip Linear samples or just the order form? Did they offer the free 9 sample sheet (I had them ship both in the same package)? Are the posted images ones you’ve taken or from the Luminit site?

At the time I wrote the first post, I hadn’t yet looked closely at the Linear samples and didn’t realize that only one of the 7 strips project a circular beam, 60 x 60 degrees (the rest are elliptical or line). Their order form is not clear on this; so I assumed the sample angles were similar to the 9 sample sheet. The 9 sample sheet has three circular samples and 6 elliptical.
Craig Gerard wrote:I would be interested to see what happens when a beam of light is shone through each of the nine LSD samples with consideration of possible application for macro.
I assume you’re trying to decide which material might be best for a particular macro lighting configuration? That’s what I’m currently debating before purchasing an 8 x 10 inch sheet of one specific “ideal” material ($49ea).

As you may have read on the Luminit site, the quality and divergence angle of the exit beam is directly dependant on the width, distribution and degree of collimization of the source beam. So far, I've tested this using a green laser pointer (fully collimated source, but narrow) and several LED flashlights with various beam widths, uniformities and degrees of collimization. The laser best shows the divergence angle and spot profile (light distribution) on both axes, while the flashlight shows the degree of “homogenization” and may better represent what the illumination (from LED, flash or FO) might look like on a macro subject.

I think what may be a more important quality for a diffuser used in macro illumination is not what the projected beam looks like reflected off of a white surface, but rather how well the diffuser “hides” any non-uniformities in the source, from the subject’s point of view. When I get a moment, I’ll post some shots of a point source as seen through the 9 samples. Based on my eyeball observations, this will reveal more differences between the samples than the white surface test.
Bob in Orange County, CA

Craig Gerard
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Post by Craig Gerard »

Bob^3,

I don't have the sample sheets. The images in my previous post were sent to me by Luminit via email.

The LSD looks like the way to go, I wouldn't be too interested in the Linear samples (they are designed for strip lighting features); but still worth investigating via the separate sample sheet. The LSD 40° Circular looks promising.
Bob^3 wrote:I think what may be a more important quality for a diffuser used in macro illumination is not what the projected beam looks like reflected off of a white surface, but rather how well the diffuser “hides” any non-uniformities in the source, from the subject’s point of view. When I get a moment, I’ll post some shots of a point source as seen through the 9 samples. Based on my eyeball observations, this will reveal more differences between the samples than the white surface test.
I'm also curious how well the LSD maintains the distribution, uniformity of light at close range to subject. A wall would be a good initial subject. Another observation I use is to point the diffuser/softbox at a shiny, reflective LCD screen (turned off) and see via reflection what is happening with the output (LED torch, flash). The key here is the 'hotspot'. How well does the LSD distribute the 'hotspot' at close range to subject (3" to 6")?

Craig
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

Rusty
Posts: 146
Joined: Mon Jul 05, 2010 5:54 am
Location: Mosselbay South Africa

Post by Rusty »

DQE wrote:
.....Per my best but no doubt limited understanding, an illuminated diffuser that occupies a large percentage of the space surrounding the subject is better than one that does not provide this feature.......
I am in the same mind, i don't think the main attribute of a diffuser should be perfect uniformity of radiation, but rather covering as large as possible an area as viewed from the subjects point of view
This can be achieved in my view by either wrapping the diffuser around the subject (curved ) or a larger diffuser further away
After all, an overcast sky gives excellent light and can be considered as a 180 degree domed diffuser with a diffused hot spot at the suns position
a gentle graduation in light intensity from the center outwards towards a feathered edge would in my view be a good way to mimmick natural light , if that is the goal
Daniel

Blcak
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Post by Blcak »

I wonder if anyone has followed up on this trace!?
It's been a while and it seemed quite promising.

canonian
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Post by canonian »

Blcak wrote:I wonder if anyone has followed up on this trace!?
I received a sample sheet from Luminit.
It's a transparant A4 sheet with small squares of LSD , various examples of their product line.
These squares are very small; big enough to see the characteristics of the material when lit from behind by a single LED but unfortunately to small to use or test it in the field of macrophotography.
It became one of many longer running 'projects' :) and haven't tested this thoroughly.

I agree it is still very promising and of great potential in diffusing harsh light.
The lighting I often use consist of 8 powerleds, and although properly diffused with what is at hand like plastics or polystyrene, it leaves a 'signature' on shiny object and can sometimes mislead its shape.
I'm positive the Luminit LSD's would solve this problem.

Blcak
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Post by Blcak »

I've tried an LCD-diffusor, which unfortunately resulted in a linear pattern. Crossing two sheets at 90° resulted in a round pattern, but also reduced the light quite a bit.

I wonder if there's a source for "normal" diffusion at good sizes. Could be very promising for light diffusion in the field.

canonian
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Post by canonian »

Blcak wrote:I've tried an LCD-diffusor, which unfortunately resulted in a linear pattern.
You probably have used the 50° X 10° sample.(see below)
Craig Gerard wrote:I would be interested to see what happens when a beam of light is shone through each of the nine LSD samples with consideration of possible application for macro.
I have put all the samples of the sheet I received from Luminit to a simple test using a 2.3Watt PowerLED and a laserpointer.
The 80° diffuser works to my satisfaction.
From the 80° diffuser samples I've cut out small round filters to place in front of my powerLEDS.
The 30° diffusion difusses somewhat less but loss of light is also less then with the 80° diffusor.

Image
Last edited by canonian on Fri Dec 28, 2012 12:06 pm, edited 1 time in total.

Blcak
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Post by Blcak »

The 80° one looks amazingly even.
Is there a source for larger sheets?

Edit: I've used the 40°*0.2° ;)

Edit2: the 30° might be a better choice for larger sheets + flash, I guess?
Hm.

Will they ship a sample to non-company people?
Last edited by Blcak on Fri Dec 28, 2012 10:40 am, edited 2 times in total.

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