Optical birefringence (plastic rainbow effect)

anotherscotsman

macrumors 68020
Original poster
Aug 2, 2014
2,105
13,858
UK
After another rainy day, I looked to explore the phenomenon of optical birefringence.

This effect occurs when polarised light passes through certain transparent objects that contains a range of molecular alignments. Changes in molecular alignment and small differences in thickness result in the polarised light taking different times to pass through the object. When these 'rays' of light exit the object, they cause an interference pattern that can be seen as a rainbow effect. This is similar to the effect we say with the light being reflected from the surfaces of the bubble film in the Soap Bubble Macro project.

Enough science - how do we do it?

1. What we need:

A source of polarised light. You can buy sheets of polaroid film to place in front of any light source but unless you have it to hand then you have to order online. You could use the lens from a pair of polaroid sunglasses but this makes your light source small. A convenient polarised light source is an LED computer display (eg iMac or iPad but brand is not important).

You also need a polarising filter for the front of your lens. Most landscape photographers, myself included, use a polarising filter to reduce glare and increase saturation in landscape photos. Again, like the source, you could use a lens from a polaroid sunglass but this is not convenient (see later).

Something transparent. Many crystals and plastic objects work well but part of the fun is to explore what works.

2. How-To:

(a) Place the test object (in this example a CD case) in front of your polarised light source:

RMG_8364.jpg

(note: the tin of The Broons Scottish Fudge is optional)



RMG_8367.jpg

(focussed-in on the transparent part of the CD case)

(b) Then attach the polariser filter to the front of your lens:

RMG_8368.jpg

As if by magic, rainbow colours appear.

(c) Rotate the polariser on the front of the lens and watch the light-source go black indicating full cross-polarisation:

RMG_8369.jpg

Colours begin to pop!

3. Post processing

Very little or no work needed to get the final image - perhaps darken the blacks a fraction and brighten the mid-tones as we did with the bubbles.

4. What to use?

Have fun experimenting with what works and what doesn't. Here is a bit of food packaging as you've never seen it:

RMG_8371.jpg


Many thin, blow-moulded plastic objects will work well but many cast- or pour-in-place resin materials won't (since they have fewer stress zones in the polymer that result in the changes in molecular alignment

Hope this helps you pass an hour or two on a wet weekend and I promise it is a lot less frustrating than trying to blow and catch bubbles :)
 
Last edited:

Clix Pix

macrumors demi-goddess
Oh, cool! Actually, one day a while back I was waiting for something to download in the computer and my eye fell on a plastic box that was sitting on the workstation, and the light was reflecting in it much in the way you've described, although there was no polarizer filter nearby. I snapped a few shots with my iPhone just for fun. I'll have to see if I've got a polarizer filter that will fit on my macro lens. Another way I've found the rainbow effect is also by using actual (blank) CDs and sprinkling a little water on them.....One gets really interesting results from that!

There is also using a prism.... somewhere I've got a couple of prisms which can create neat results, too. Haven't played with those in a long time. Goody, this inspires me to look for those prisms, repurpose a CD case without the CD and also to do the thing with the CD as well..... That should provide many happy hours for me and my beloved 90mm macro lens!
 

anotherscotsman

macrumors 68020
Original poster
Aug 2, 2014
2,105
13,858
UK
Oh, cool! Actually, one day a while back I was waiting for something to download in the computer and my eye fell on a plastic box that was sitting on the workstation, and the light was reflecting in it much in the way you've described, although there was no polarizer filter nearby. I snapped a few shots with my iPhone just for fun. I'll have to see if I've got a polarizer filter that will fit on my macro lens. Another way I've found the rainbow effect is also by using actual (blank) CDs and sprinkling a little water on them.....One gets really interesting results from that!

There is also using a prism.... somewhere I've got a couple of prisms which can create neat results, too. Haven't played with those in a long time. Goody, this inspires me to look for those prisms, repurpose a CD case without the CD and also to do the thing with the CD as well..... That should provide many happy hours for me and my beloved 90mm macro lens!
a
As you’ve seen, you don’t need the lens polariser to generate the effect - it allows you to black-out the polarised light source to maximise the visibility of the rainbow. CDs, bubbles prisms, butterfly wings - all the same basic phenomenon.
 
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Clix Pix

macrumors demi-goddess
Fascinating, isn't it? All of this is playing with light and the magical things it can do.....

Just took a quick look in my iPhone and I still had the image of the plastic box in there. It was picking up colors from the computer screen and adding a few more of its own. The round green sticker is my reminder that this is one of the containers for an external SSD that goes to the bank for safe-keeping, one that contains my photos. This is SOOC, not processed, just for fun viewing:

IMG_0409.JPG


I like the idea of using a polarizer filter when shooting something like this, as yes, it definitely will darken the environment and make the colors really pop. Gonna try this tomorrow....
 
Last edited:

Clix Pix

macrumors demi-goddess
Oh, boy, is THIS stuff FUN!!!! I've had a blast this afternoon. I found that yes, plastics are better at this than crystal, although I did find one piece of crystal that lit up beautifully when I set it in front of the LCD monitor. I posted that one in the POTD thread. Here's another sample of today's fun -- plastic utensils are ideal for this kind of project! They are standing in a plastic container that I often use upside down to get my subjects to the right height, and in turn that is standing on the largest one.....

What's for dinner?

What's For Dinner?.jpg
 

anotherscotsman

macrumors 68020
Original poster
Aug 2, 2014
2,105
13,858
UK
Oh, boy, is THIS stuff FUN!!!! I've had a blast this afternoon. I found that yes, plastics are better at this than crystal, although I did find one piece of crystal that lit up beautifully when I set it in front of the LCD monitor. I posted that one in the POTD thread. Here's another sample of today's fun -- plastic utensils are ideal for this kind of project! They are standing in a plastic container that I often use upside down to get my subjects to the right height, and in turn that is standing on the largest one.....

What's for dinner?

View attachment 893660
Glad you like it - passes a dull afternoon 😀
 
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Clix Pix

macrumors demi-goddess
It's fun doing this stuff and exploring what one can do with what is already available or which can be readily assembled -- I have really been enjoying the bubble rainbow earth, the plastic rainbow effect (birefringence), playing with food coloring, and also returning to something I'd done a long time ago, shooting the amazing effects of water drops/water-and-glycerine drops -- on a blank CD under lots of sunlight. It's amazing what interesting results we can get from experimenting with all of these (and undoubtedly there are more to explore!). All of this has kind of sparked that tiny flickering of creativity that I apparently have within me somewhere.....not to mention arousing my sense of determination and "by-gum-I'm-gonna-figure-this-out!" when things aren't going as I would have expected. :D

All of these are interesting and potentially challenging projects to investigate on a yucky and cold winter's day or when one is bored and wants to shoot something with nearly instant impact and which is likely to turn out totally different than expected, a fun surprise. Certainly nothing to maintain as a steady diet, so to speak, but it does help with those days when one wants to shoot something -- anything -- and weather isn't cooperating, inspiration just isn't there, etc. This also is a good reminder to me that macro lenses can come in handy for all kinds of subjects, not just insects and flowers. Actually, I don't like shooting and sharing the same thing over and over again, so for me this has been great during the often uninspiring days of winter, especially in this particular year when in my area we really have not had any snow to speak of, or intriguing ice images to capture. I'm happy about the warmer, milder winter but it does limit what's available for shooting if one wants to be outdoors.....

Thanks, AnotherScotsman! You have been the source of providing much delight for me these past few weeks!
 

kenoh

macrumors demi-god
Jul 18, 2008
5,451
8,341
Glasgow, UK
After another rainy day, I looked to explore the phenomenon of optical birefringence.

This effect occurs when polarised light passes through certain transparent objects that contains a range of molecular alignments. Changes in molecular alignment and small differences in thickness result in the polarised light taking different times to pass through the object. When these 'rays' of light exit the object, they cause an interference pattern that can be seen as a rainbow effect. This is similar to the effect we say with the light being reflected from the surfaces of the bubble film in the Soap Bubble Macro project.

Enough science - how do we do it?

1. What we need:

A source of polarised light. You can buy sheets of polaroid film to place in front of any light source but unless you have it to hand then you have to order online. You could use the lens from a pair of polaroid sunglasses but this makes your light source small. A convenient polarised light source is an LED computer display (eg iMac or iPad but brand is not important).

You also need a polarising filter for the front of your lens. Most landscape photographers, myself included, use a polarising filter to reduce glare and increase saturation in landscape photos. Again, like the source, you could use a lens from a polaroid sunglass but this is not convenient (see later).

Something transparent. Many crystals and plastic objects work well but part of the fun is to explore what works.

2. How-To:

(a) Place the test object (in this example a CD case) in front of your polarised light source:

View attachment 893522

(note: the tin of The Broons Scottish Fudge is optional)



View attachment 893523

(focussed-in on the transparent part of the CD case)

(b) Then attach the polariser filter to the front of your lens:

View attachment 893524

As if by magic, rainbow colours appear.

(c) Rotate the polariser on the front of the lens and watch the light-source go black indicating full cross-polarisation:

View attachment 893525

Colours begin to pop!

3. Post processing

Very little or no work needed to get the final image - perhaps darken the blacks a fraction and brighten the mid-tones as we did with the bubbles.

4. What to use?

Have fun experimenting with what works and what doesn't. Here is a bit of food packaging as you've never seen it:

View attachment 893526

Many thin, blow-moulded plastic objects will work well but many cast- or pour-in-place resin materials won't (since they have fewer stress zones in the polymer that result in the changes in molecular alignment

Hope this helps you pass an hour or two on a wet weekend and I promise it is a lot less frustrating than trying to blow and catch bubbles :)
You might also need to explain who the Broons are for the uneducated on here.
 
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