LSD for macro photographers (high-tech diffusion material)

A forum to ask questions, post setups, and generally discuss anything having to do with photomacrography and photomicroscopy.

Moderators: Pau, rjlittlefield, ChrisR, Chris S.

rjlittlefield
Site Admin
Posts: 21134
Joined: Tue Aug 01, 2006 8:34 am
Location: Richland, Washington State, USA
Contact:

Post by rjlittlefield »

canonian wrote: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.
Now you've made me curious. Can you show us the lighting setup that you're using and the signature that it produces?

--Rik

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

Post by DQE »

Regarding the use of a laser pointer to test this type of diffuser:

is the use of coherent light interpretable in this context, where the ultimate goal is to create and use highly diffuse (and of course incoherent) light?

I guess what I'm getting at is that many times when I use coherent light, things happen that simply don't happen with incoherent light, including speckle and various specialized types of diffraction.
-Phil

"Diffraction never sleeps"

canonian
Posts: 890
Joined: Tue Aug 31, 2010 4:00 am
Location: Rotterdam, Netherlands
Contact:

Post by canonian »

Blcak wrote:Will they ship a sample to non-company people?
I had no trouble ordering a sample as a 'non-company' consumer.
rjlittlefield wrote: Now you've made me curious. Can you show us the lighting setup that you're using and the signature that it produces?
Rik , I gladly like to show the lighting setup.
The "OctoLite" as I like to call it:

Image

I made you curious because of my bad choice of words I guess.
The "signature" I'm talking about are the eight hotspots it reflects on shiny objects.

Two examples:

The "odd eyes", mis-shaped by the reflection of the LEDring. Is it anatomy or illumination?
Image

Hotspots in the droplets, created by the LEDRing:
Image

The hotspots are now better diffused, using both a polystyrene cup and the LSD diffusers in front of the collimatorlens of the PowerLED.
It's still hard to create a soft, even lighting. The hotspots --although vaguely-- still show up in the reflecting object.

Image

DQE wrote:...is the use of coherent light interpretable in this context
In the diffusertest I used the laser to show the amount of 'scatter' the different diffusers would produce, and I used the PowerLED because it's the type of lighting I use in my lighting setup, being more a practical situation.

rjlittlefield
Site Admin
Posts: 21134
Joined: Tue Aug 01, 2006 8:34 am
Location: Richland, Washington State, USA
Contact:

Post by rjlittlefield »

canonian wrote:
rjlittlefield wrote: Now you've made me curious. Can you show us the lighting setup that you're using and the signature that it produces?
I made you curious because of my bad choice of words I guess.
The "signature" I'm talking about are the eight hotspots it reflects on shiny objects.
This is actually what I expected to see.
The hotspots are now better diffused, using both a polystyrene cup and the LSD diffusers in front of the collimatorlens of the PowerLED.
It's still hard to create a soft, even lighting. The hotspots --although vaguely-- still show up in the reflecting object.
I hate to be a pest, but now I would like to see a wider view of the whole setup, showing separations between the LEDs, the LSD diffusers, the polystyrene cup, and the subject.

The reason I'm asking these questions is to help understand what's causing the hot spots. There is a common confusion between where the light goes to (starting from the light source) and where the light comes from (ending up at the subject). To eliminate the hot spots you're talking about, the light has to come from a uniformly emitting area around the subject. Since you're still seeing hot spots, apparently the innermost layer of diffusion is either not uniformly illuminated itself, or it's not completely scrambling the light that hits it, or both. Seeing the overall setup will help to figure out what's happening.

--Rik

canonian
Posts: 890
Joined: Tue Aug 31, 2010 4:00 am
Location: Rotterdam, Netherlands
Contact:

Post by canonian »

rjlittlefield wrote:I hate to be a pest, but now I would like to see a wider view of the whole setup, showing separations between the LEDs, the LSD diffusers, the polystyrene cup, and the subject.
No pest at all Rik . This is my attempt of an "Exploded View".The LEDs are dimmed.
Usually the subject and the cup are raised withing the center of the lights, or the cup is upside down, around the lens.

The LSD samples were very small so I cut them into round filters and used them in front of the collimatorlens of the PowerLED .
If I had more of this material I would choose to make a tube between the lights and the subject to get a better spread of the light.
(A diffusertube I sometimes use can be seen in the background. No LSD but the diffuser from a discarded LCD monitor)
Cutting small filters helps a bit but is not an efficient use of the LSD's.

Image

rjlittlefield
Site Admin
Posts: 21134
Joined: Tue Aug 01, 2006 8:34 am
Location: Richland, Washington State, USA
Contact:

Post by rjlittlefield »

That's a wonderfully explanatory picture -- thanks much!

Your polystyrene cup looks like the ones I'm familiar with. Mine are almost perfect diffusers in the sense of completely scrambling whatever light gets through them. Shine a laser pointer through yours, and I expect what you'll get out the back side is a red glow over everything in the vicinity. However, like all sheet materials they do not spread light very far within the sheet -- whatever pattern of light strikes one side is reproduced with only modest blurring on the other side.

So, what I think is happening is that the LEDs with their collimators and LSD sheets are shining a pattern of hotspots onto the outside of the cup, and the cup is dutifully relaying that pattern to the inside of the cup from where it can be reflected by the subject.

Your idea of making a tube of the LSD material could definitely help, but not if it simply replaces the polystyrene cup. Instead, you would need to have multiple layers of diffusion with significant space between them so that light ends up striking the inner diffuser in a uniform pattern, even though it's nonuniform at the outer diffuser. The advantage of LSD for this use would be its efficiency. From the standpoint of uniformity, two layers of white paper arranged in the same way would work just as well.

--Rik

canonian
Posts: 890
Joined: Tue Aug 31, 2010 4:00 am
Location: Rotterdam, Netherlands
Contact:

Post by canonian »

rjlittlefield wrote:Your idea of making a tube of the LSD material could definitely help, but not if it simply replaces the polystyrene cup. Instead, you would need to have multiple layers of diffusion with significant space between them ...
It always help to have someone else look at the situation. Thank you for the insight you gave me, Rik.
Indeed all the polystyrene did was following and passing thru the hotspot circle from the LED's. I was hoping it would blur out the circles of light, but it didn't.

This time I folded up a sheet of diffusermaterial ( again from the broken LCD monitor, great DIY material !) twice and much improvement can be seen.
I seems bigger distance between the light and the tube is key.

Not a very scientific approach because two parameters has now changed: distance and material. Also the diffuser material has a shiny side and a matte side, which is folded inwards, on the inside of the tube.
I think this is the path I have to follow. Next (not now it's getting late here across the pond) I'll try an inner and outer tube of diffuser material but the results so far looks promising.
Maybe two tubes make me lose a significant amount of light but the power LEDs can handle this, at least at low magnification.

Image
Two layers of diffuser material

Image
I upped the exposure a bit in PP to see the band of light, with less hotspots, or at least the beams of light are overlapping now



Edit: typo's
Last edited by canonian on Sat Dec 29, 2012 3:37 am, edited 1 time in total.

Chris S.
Site Admin
Posts: 3549
Joined: Sun Apr 05, 2009 9:55 pm
Location: Ohio, USA

Post by Chris S. »

Rather than use this material to provide simple diffusion, I keep thinking that it might provide a good way to direct light from a linear-shaped flash tube into the round shape of a fiber optic light guide. How to do this efficiently is an old question, and holographic diffusers might provide a better answer than others studied before.

Check out this composite of images from the Edmund Optics Webpage on holographic diffusors.
Image

I did some very rudimentary testing of such an approach, but my interests moved from flash to halogen. For flash shooters using fiber optics, I suspect this would work.

Cheers,

--Chris

--edited for clarity
Last edited by Chris S. on Sat Dec 29, 2012 1:27 pm, edited 1 time in total.

enricosavazzi
Posts: 1291
Joined: Sat Nov 21, 2009 2:41 pm
Location: Borgholm, Sweden
Contact:

Post by enricosavazzi »

Just a thought going off on a tangent: microlens array sheets and similar low-loss diffusers are expensive and difficult to find (except for recycling the components of some LCD panels), but thin Fresnel lenses marketed as reading magnifiers (and quite poor for this purpose) are common and cheap.

Any chance we can use two, three or four layers of these as diffusers, including their peripheral regions instead of using just the center region and discarding the rest? and how to orient these layers with respect to each other, in practice, to get the best diffusion? Would it be enough with two layers where the Fresnel grooves are roughly perpendicular to each other?
--ES

Blcak
Posts: 34
Joined: Wed May 09, 2012 6:19 am
Location: Switzerland (originally)

Post by Blcak »

Are microlens arrays really "expensive"?

I've not been able to find a price. I'll contact a distributor to find out, but that'll take a while these days.
canonian wrote:
Blcak wrote:Will they ship a sample to non-company people?
I had no trouble ordering a sample as a 'non-company' consumer.
With "sample" I meant larger sheets of the 30° and 80° (most interesting, imho).

rjlittlefield
Site Admin
Posts: 21134
Joined: Tue Aug 01, 2006 8:34 am
Location: Richland, Washington State, USA
Contact:

Post by rjlittlefield »

enricosavazzi wrote:Just a thought going off on a tangent: microlens array sheets and similar low-loss diffusers are expensive and difficult to find (except for recycling the components of some LCD panels), but thin Fresnel lenses marketed as reading magnifiers (and quite poor for this purpose) are common and cheap.

Any chance we can use two, three or four layers of these as diffusers, including their peripheral regions instead of using just the center region and discarding the rest? and how to orient these layers with respect to each other, in practice, to get the best diffusion? Would it be enough with two layers where the Fresnel grooves are roughly perpendicular to each other?
This does not sound promising to me. The periphery of a Fresnel lens is very much like the periphery of an ordinary lens with the same focal length, except for more scattering off the edges of facets. Its main effect on the laser pointer will be to bend the beam, not spread it. Two perpendicular layers should get you a different bend and some more scattering, but nothing like the smooth spreading provided by the micro lens arrays that have a specific distribution of shapes and slants to do that. See figure 2 at http://www.photonics.com/Article.aspx?AID=41972.

--Rik

enricosavazzi
Posts: 1291
Joined: Sat Nov 21, 2009 2:41 pm
Location: Borgholm, Sweden
Contact:

Post by enricosavazzi »

An interesting reference I just found. This web site owner was able to build a plenoptic camera as a hobby project, including its microlens sheet:

http://cameramaker.se/plenoptic.htm
--ES

Tom Jones
Posts: 304
Joined: Sat Jan 31, 2009 2:05 am
Location: Crestline, CA

Post by Tom Jones »

Fred,

What model of led assembly are those and what are you using as a dimmer?

Tom

enricosavazzi
Posts: 1291
Joined: Sat Nov 21, 2009 2:41 pm
Location: Borgholm, Sweden
Contact:

Post by enricosavazzi »

rjlittlefield wrote:
enricosavazzi wrote:Just a thought going off on a tangent: microlens array sheets and similar low-loss diffusers are expensive and difficult to find (except for recycling the components of some LCD panels), but thin Fresnel lenses marketed as reading magnifiers (and quite poor for this purpose) are common and cheap.

Any chance we can use two, three or four layers of these as diffusers, including their peripheral regions instead of using just the center region and discarding the rest? and how to orient these layers with respect to each other, in practice, to get the best diffusion? Would it be enough with two layers where the Fresnel grooves are roughly perpendicular to each other?
This does not sound promising to me. The periphery of a Fresnel lens is very much like the periphery of an ordinary lens with the same focal length, except for more scattering off the edges of facets. Its main effect on the laser pointer will be to bend the beam, not spread it. Two perpendicular layers should get you a different bend and some more scattering, but nothing like the smooth spreading provided by the micro lens arrays that have a specific distribution of shapes and slants to do that. See figure 2 at http://www.photonics.com/Article.aspx?AID=41972.

--Rik
Hi Rik,

yes, I can see how a good Fresnel lens would not make a reasonable diffuser. I was thinking that, poor as these Fresnel lenses actually are in practice, enough light would follow unintended paths to make them work, in practice, as diffusers, especially if two or more layers are used. Fresnel lenses have a set of surfaces intended to transmit light and a second set not intended to, near-perpendicular to the lens backing. This second set might help to reflect/refract light in multiple directions. But I do agree that a proper microlens sheet will make a much better diffuser.
--ES

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

Post by DQE »

In addition to enjoying this thread's multi-faceted optics discussions, I am eagerly looking forward to someone posting a link to a simple thin sheet "diffuser" that will magically convert my small Canon MT-24 twin-flash units to effectively much wider and highly diffuse flash units. Due to an overactive imagination, all I will need to do is to tape a couple of sheets of semi-exotic high-tech flash modifiers onto my MT-24 flash heads and all my macro photos will be pleasantly and of course diffusely illuminated and without bright spots.

Science fiction, wishful thinking or just silly?

<Insert friendly smiles here>
-Phil

"Diffraction never sleeps"

Post Reply Previous topicNext topic