DIY Polarized light

[Javier]

Hi,

I'm looking forward to trying some DIY polarized light techniques. Can you tell from this image if these regular 3d glasses will do the job? The seller does not offer a detailed description.

TIA.

[PeteM]

If you're trying to add simple polarization to a microscope, you're better off buying cheap camera polarizers. These are available in sizes small enough for cell phones, in lots of sizes from the mid 30mm to 52mm or so to fit the field apertures of compound microscopes, and even large enough to serve as a stereo microscope stage. A range from perhaps 14mm to 95mm or more. The Chinese ones are cheap and sandwiched between glass. You may have to flip the orientation to get extinction, since many will be circular rather than linear polarizers. Cost for one for the bottom field aperature and one to fit between the objectives and the head - maybe $20 for both.

There are also Ebay sellers with rigid linear polarizers cut to various diameters. These would also be better than the 3D glasses, even without being sandwiched between glass.

Compared to those 3D glasses the camera polarizers will be flat, more durable glass rather than plastic surfaces, with better optics, and in useful sizes without cutting them. Compared to OEM polarizers, they typically won't have quite as good extinction when crossed. Good enough, though, for most simple polarization.

The trick is finding a place and size that will fit between the stand and the head. Perhaps 2/3rd of compound microscopes can be somewhat easily adapted. Perhaps a third won't have enough space or a recess to fit even a small polarizer. If not, the better ones will have dedicated "intermediate" pieces for polarizers/analyzers - but the cost might be a couple hundred dollars (used) or more.

[Javier]

Hi Pete, thanks for your input.

Indeed, I'm trying to add simple polarization to my regular bright field microscope. It makes sense to buy some cheap camera filters. In fact, I have one 1,25 filter from my scopes, so I would only need one more.

The trick is finding a place and size that will fit between the stand and the head. Perhaps 2/3rd of compound microscopes can be somewhat easily adapted. Perhaps a third won't have enough space or a recess to fit even a small polarizer. If not, the better ones will have dedicated "intermediate" pieces for polarizers/analyzers - but the cost might be a couple hundred dollars (used) or more.

I was thinking of placing one filter under the slide and the other on top, as I saw in some of Oliver's tutorials (image attached). Do you think this would work?

[Javier]

Indeed, I'm trying to add simple polarization to my regular bright field microscope.

Let me rephrase that. I'm trying to have some fun playing with polarized light. No high expectations whatsoever.

[PeteM]

The polarizers will work immediately above and below the slide, but not as well as the previously suggested spots. Three minor problems:

- You're more like to get dirt or smudges on (or scratch) the polarizers if you handle them as a "sandwich" with a slide.
- At low power those smudges or scratches can show up in the image plane.
- It's easier to rotate a polarizer located on the field lens than one just above or below a slide

[Javier]

Great, thank you!

[SilverWolf]

You can get some CP filters as small as 25mm on eBay, I was thinking of glass instead of plastic myself also and was just looking about myself.

I was hoping a 25-30mm would sit in under my trinocular head and then use say a 40mm between my LED and the condenser that I could rotate freely. I'm a newbie but I'm hoping that will work and be better than plastic film I hope, cost like $10 each roughly.

https://www.ebay.com.au/itm/25mm-27mm-2 ... 3587212276

Thinking something like these filters and use a small rotary tool to cut the metal ring off the smaller filter I drop into my camera port/head so it can sit flat.

[Javier]

Thinking something like these filters and use a small rotary tool to cut the metal ring off the smaller filter I drop into my camera port/head so it can sit flat.

Most if not all filters have a retaining ring that can be unscrewed to separate the optical glass from the monting ring.

[Hobbyst46]

Please see response #28 here
viewtopic.php?f=5&t=9957&p=85365&hilit=SVbony#p85365

[SilverWolf]

Thinking something like these filters and use a small rotary tool to cut the metal ring off the smaller filter I drop into my camera port/head so it can sit flat.

Most if not all filters have a retaining ring that can be unscrewed to separate the optical glass from the monting ring.

Please see response #28 here
viewtopic.php?f=5&t=9957&p=85365&hilit=SVbony#p85365

Thank you both for the helpful info/confirmation, sounds way too easy but who doesn't like easy

[Javier]

So, I bought an used Japanese 37 mm filter for two dollars in mint conditions, but things did not go well so far.

I couldn't get this filter and my previous 1,25" filter to work at all. The new filter seems to be a variable polarizer of some sort, because there are two slim filters cemented. When looking through that filter to a monitor or a cell phone, it will darken to extinction, but won't interact with the other filter at all. Also, this effect won't be seen at the scope...

I'm thinking the problem is this doublet camera polarizer, but splitting them is an impossible task, I will en up broken the filter to pieces.

Any ideas?

[Greg Howald]

The paper glasses you are looking at are sold on Amazon. They are circular rather than Linear polarization filters. They will work only in one orientation. Flipping them over and fiddling with them to find the right combination is normal behavior with them.
And they are very easily scratched. You can but 10 pair for $12.99 and go through them pretty quickly or you can spend a little more for things that work and last.
Greg

[SWmicro]

Japanese 37 mm filter
there are two slim filters cemented.
but splitting them is an impossible task,
Any ideas?

Hi,
I have been down this rabbit hole and here is what I think :-
Splitting them would not help much anyway!

This is because one layer is a linear polarizer (LP) which we want and the other is a thing called a "quater wave plate" (QWP) which we dont need - and which with the linear, makes the combination a circular polarizer in one direction only. If you flip it over then it reverts to being just LP, the QWP is then of little consequence when we use it this way round in a microscope. (I think it changes the expected colours when used with other birefringent objects but they are easily changed by rotation anyway)

I started out as you are, and got very confused so I eventually ended up with 2 circular and 2 linear camera filters, cheap on ebay in England, [plus some foil repair sheets for cellphones, more on that later if you want].
These 2 circulars can be used in the reverse orientation either with each other, or 1 circular + 1 linear, in the microscope.

Just to make sure we know where we are :
tell us what happens with your new 37mm, does it extinct your monitor/cellphone when looking through one way only, with little effect the other way round ?

Same question for your old 1.25" (it may not be a polarizer at all !)

[Javier]

Japanese 37 mm filter
there are two slim filters cemented.
but splitting them is an impossible task,
Any ideas?

Hi,
I have been down this rabbit hole and here is what I think :-
Splitting them would not help much anyway!

This is because one layer is a linear polarizer (LP) which we want and the other is a thing called a "quater wave plate" (QWP) which we dont need - and which with the linear, makes the combination a circular polarizer in one direction only. If you flip it over then it reverts to being just LP, the QWP is then of little consequence when we use it this way round in a microscope. (I think it changes the expected colours when used with other birefringent objects but they are easily changed by rotation anyway)

I started out as you are, and got very confused so I eventually ended up with 2 circular and 2 linear camera filters, cheap on ebay in England, [plus some foil repair sheets for cellphones, more on that later if you want].
These 2 circulars can be used in the reverse orientation either with each other, or 1 circular + 1 linear, in the microscope.

Just to make sure we know where we are :
tell us what happens with your new 37mm, does it extinct your monitor/cellphone when looking through one way only, with little effect the other way round ?

Same question for your old 1.25" (it may not be a polarizer at all !)

Oh my... and here I was thinking "let's try this polarizing light that sounds easy and fun "

You are right, the QWP acts exactly as you described it. The old filter is sold as a polarizer filter for astronomy. Do you think it could be not a polarizer at all? I noticed that most polarizer camera filters have a ring to rotate them, are they all QWP?

Thanks for your help.

[Javier]

As for my old 1,25" filter, it is a simple layer filter and it does not produce any effect when rotating it in front of my monitor or cellphone.

[SWmicro]

As for my old 1,25" filter, it is a simple layer filter and it does not produce any effect when rotating it in front of my monitor or cellphone.

Sounds like it may not be a polarizer then, just a neutral density filter ? It should extinct both ways if linear, or only one way if circular (I think ,,, I will check later to make sure )
If a an astronomy variable polarizer I would expect 2 linears in a mount in which one can be rotated rel. the other ??
I have seen them advertised as variable moon filters but not used one ( my eyes can accommodate the moon in all my scopes up to my 9.25" (not used my 12" on the moon yet !) )
I can later describe a mirror test for circular for you, but my domestic is calling me !! you may be able to google for it.

[Javier]

As for my old 1,25" filter, it is a simple layer filter and it does not produce any effect when rotating it in front of my monitor or cellphone.

Sounds like it may not be a polarizer then, just a neutral density filter ? It should extinct both ways if linear, or only one way if circular (I think ,,, I will check later to make sure )
If a an astronomy variable polarizer I would expect 2 linears in a mount in which one can be rotated rel. the other ??
I have seen them advertised as variable moon filters but not used one ( my eyes can accommodate the moon in all my scopes up to my 9.25" (not used my 12" on the moon yet !) )
I can later describe a mirror test for circular for you, but my domestic is calling me !! you may be able to google for it.

Yes, astronomy polarizers are sold as you described them: two linear in a mount that can be rotated. I used to have one, but it was quite messy on reflections.

I'm confused with what you are saying about a single polarizing -linear or circular- producing extinction. What's the point of using two of them then?

[SWmicro]

I'm confused with what you are saying about a single polarizing -linear or circular- producing extinction. What's the point of using two of them then?

Sorry, my fault for missing some words out :
When looking at a monitor/cellphone screen through a filter it will -
(A) if it is a circular, extinct in only one orientation. When flipped back to front it will have little effect.
(B) extinct both ways if it is a linear
(C) and neither, of course, if just a ND filter
All that was only for the purpose of testing what type(s) of filters you have, or may acquire.

When using in a microscope you need 1 linear* to polarize the random light source (ie. make it behave like your cellphone screen, which has built in polarizers)
then the 2nd linear* (above the slide) to analyse the birefringence of the sample, and any included wave plate, by the change of colours the sample makes.
*or circulars behaving in linear mode in the correct flip.

[SWmicro]

are they all QWP?

I'm in danger of exceeding my pay grade here ! I think :-
that all the circular ones will be the double layer with a QWP

In the olden days of film slr, (with or without range finder manual focus), the anti-glare/reflection filters were single layer linear and are still about for particular purposes.
With the advent of dslr with fancy autofocus gizmos, some get confused by linear so the light entering the lens needed to become circular by passing through the QWP, after the anti-reflection having been accomplished by the front linear element.
Caveat - I think some autofocus (Nikon ?) are even more clever and can use linear ie. without need of a QWP ?????

I stand to be corrected on all of that

[Javier]

Thank you for the interesting data.

I will try to get the system to work with all this in mind.

[EYE C U]

OLDER CAMERA LENSES DIDN'T SPIN WHEN FOCUSED SO LINEAR POL WORKED FINE....NEWER LENSES, THE FRONT WOULD SPIN AND CHANGE THE POL EFFECT OF A LINEAR FILTER..