DIY polarization

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victhree
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DIY polarization

#1 Post by victhree » Sun Jan 02, 2022 8:47 pm

Evening, everyone

I've been having tons of fun with my 2nd hand microscope. Since my budget is basically 0, part of the fun has been trying to overclock the thing with homemade filters and cheap parts. Now i wanna dip my toes into polarization techniques, but I have a couple of questions:

1. Linear or circular? I've read a couple of comments arguing that it doesn't really matter, but I'd like to hear your experiences with both.

2. Physical stores which might have polarizing film? Really, this is only a problem for linear polarization, circular would be as easy as getting a couple of disposable 3d glasses (citation needed). I remember our middle school science teacher letting us play with polarizing film, but I can't for the life of me figure out where she got it. Photography filters won't work, since i'd like to cut it up and experiment with different setups.

3. Where in the optical train should I place the filters? Best spot would be directly above and below the slide, but both are pretty inconvenient in my setup. I'm afraid that separating the filters with lenses will unpolarize the light a little, but i don't know the first thing about optics, so I might be wrong. I've read that some people place the top filter inside the head, right above the hole for the objective. This would be excellent, but i'd have to build up the courage to remove the head, and i'm not sure how it would affect the final image when not using the bottom filter. I'm fine with a bit of dimming, my light doesn't go quite dim enough for extended observation, so it would actually be a welcome change.

Thanks in advance for any responses, this community is super welcoming and helpful. Happy holidays everyone!

PeteM
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Re: DIY polarization

#2 Post by PeteM » Sun Jan 02, 2022 9:51 pm

If you flip a circular polarizer to the proper orientation, it will work fine. You can probably buy two cheap camera polarizers (sandwiched in glass) for around $20 from various Chinese suppliers.

There are two things to watch with cheap polarizers (from 3D glasses, cheaper film, and cheap camera polarizers):

1) Extinction. OEM polarizers, when crossed, will have deep extinction and provide better images. Cheap ones won't.

2) Flatness. Film polarizers can sometimes introduce a bit of glare or other defects. You might be pleased enough, though.

As for placement, the lower one can fit over the field lens or in a holder below the condenser. Buy one of a diameter to fit.

The upper one can ideally fit between the stand and head. There is often enough space to fit (and leave) one in with no intermediate piece - the ideal low cost solution. Buy one of a smaller diameter to fit. If you plan to leave it in for brightfield (without the other polarizer very little light is lost), then I'd suggest one of optical (camera) quality.

In other cases you may want to buy or make an intermediate piece with a slide-in polarizer. These run around $200+ used. For finite scopes, you'll need one with a lens to correct for the added tube length. Ideally, your scope has room under the head.

Years ago, some makers had polarizer add-ons to fit above the eyepieces. As long as you get the top polarizer above the slide and away from an image plane there are multiple suitable locations.

Chas
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Re: DIY polarization

#3 Post by Chas » Sun Jan 02, 2022 10:01 pm

Circular polarising filters, like the cinema spectacle filters, are linear polarising filters with a 'twisting' layer on the front. The cinema spectacles have the linear filter on the eyeball side ... so if you have two filters out of cinema specs and put them eyeball-side facing eyeball-side ( a bit like a beetle might wear them!) then they should go black when one is rotated.

On your microscope you will want to be able to rotate one of them to get to the black postion.... the most obvious place for this one is on the top of your illiminator light, to start with.

I would then get a phillips screwdriver and undo the screw that holds on the angled head ( I looked at the photo in your initial post!) and , if you can, place the second filter in there [eyeball side down] you may have plenty of spare extra illimination,if so, you could leave this in permanently.

Try that and then, looking at the same specimen, remove your condenser and see if it is causing much of a problem to the 'darkness'.

Search ebay for polarising film, it can be bought in 50mm squares.

EDIT; I have just tried with two pairs of 3d specs and eyeball-side facing eyeball-side works..but so does cinema screen-side facing screen-side .. but one against the other doesn't.
The two ways seem slightly different in terms of the extinction .. it might be worth trying both ways. [Maybe mark the front faces of the lenses with a small dot before you take them out of their frames !]

EDIT 2: Its even more complicated than this! To get two cinema-facing sides to extinguish you need two pairs of specs ... and you need the left eye of one to face the left eye of the other and ditto the right sides.... easiest to stick with the eyeball facing sides, to start with ;-)

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victhree
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Re: DIY polarization

#4 Post by victhree » Mon Jan 03, 2022 1:03 am

PeteM wrote:
Sun Jan 02, 2022 9:51 pm
If you flip a circular polarizer to the proper orientation, it will work fine. You can probably buy two cheap camera polarizers (sandwiched in glass) for around $20 from various Chinese suppliers.

There are two things to watch with cheap polarizers (from 3D glasses, cheaper film, and cheap camera polarizers):

1) Extinction. OEM polarizers, when crossed, will have deep extinction and provide better images. Cheap ones won't.

2) Flatness. Film polarizers can sometimes introduce a bit of glare or other defects. You might be pleased enough, though.

As for placement, the lower one can fit over the field lens or in a holder below the condenser. Buy one of a diameter to fit.

The upper one can ideally fit between the stand and head. There is often enough space to fit (and leave) one in with no intermediate piece - the ideal low cost solution. Buy one of a smaller diameter to fit. If you plan to leave it in for brightfield (without the other polarizer very little light is lost), then I'd suggest one of optical (camera) quality.

In other cases you may want to buy or make an intermediate piece with a slide-in polarizer. These run around $200+ used. For finite scopes, you'll need one with a lens to correct for the added tube length. Ideally, your scope has room under the head.

Years ago, some makers had polarizer add-ons to fit above the eyepieces. As long as you get the top polarizer above the slide and away from an image plane there are multiple suitable locations.
Thanks for the response, that was very helpful! I didn't know camera filters were just regular film between two pieces of glass; definitely makes them worth considering for the top element.

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victhree
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Re: DIY polarization

#5 Post by victhree » Mon Jan 03, 2022 1:12 am

Chas wrote:
Sun Jan 02, 2022 10:01 pm
Circular polarising filters, like the cinema spectacle filters, are linear polarising filters with a 'twisting' layer on the front. The cinema spectacles have the linear filter on the eyeball side ... so if you have two filters out of cinema specs and put them eyeball-side facing eyeball-side ( a bit like a beetle might wear them!) then they should go black when one is rotated.

On your microscope you will want to be able to rotate one of them to get to the black postion.... the most obvious place for this one is on the top of your illiminator light, to start with.

I would then get a phillips screwdriver and undo the screw that holds on the angled head ( I looked at the photo in your initial post!) and , if you can, place the second filter in there [eyeball side down] you may have plenty of spare extra illimination,if so, you could leave this in permanently.

Try that and then, looking at the same specimen, remove your condenser and see if it is causing much of a problem to the 'darkness'.

Search ebay for polarising film, it can be bought in 50mm squares.

EDIT; I have just tried with two pairs of 3d specs and eyeball-side facing eyeball-side works..but so does cinema screen-side facing screen-side .. but one against the other doesn't.
The two ways seem slightly different in terms of the extinction .. it might be worth trying both ways. [Maybe mark the front faces of the lenses with a small dot before you take them out of their frames !]

EDIT 2: Its even more complicated than this! To get two cinema-facing sides to extinguish you need two pairs of specs ... and you need the left eye of one to face the left eye of the other and ditto the right sides.... easiest to stick with the eyeball facing sides, to start with ;-)
Wow, that was super thorough! Thank you so much for actually trying it out, I think I'll go with the 3d glasses for now and see how it turns out on my setup. I'm a bit scared to remove the head, but then again, I've already done some unspeakable things to the stage in order to mod it :lol:

crb5
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Re: DIY polarization

#6 Post by crb5 » Mon Jan 03, 2022 1:23 am

Here's a video to add to the previous suggestions: https://studio.youtube.com/video/iNNkdHyvhbs/edit

MichaelG.
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Re: DIY polarization

#7 Post by MichaelG. » Mon Jan 03, 2022 10:49 am

crb5 wrote:
Mon Jan 03, 2022 1:23 am
Here's a video to add to the previous suggestions: https://studio.youtube.com/video/iNNkdHyvhbs/edit
.

Could you check that link, please ?
… Google is asking me to sign-in, to edit it :?

Thanks
MichaelG.
Too many 'projects'

SWmicro
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Re: DIY polarization

#8 Post by SWmicro » Mon Jan 03, 2022 10:55 am

crb5 wrote:
Mon Jan 03, 2022 1:23 am
Here's a video to add to the previous suggestions: https://studio.youtube.com/video/iNNkdHyvhbs/edit
Ooops!
I think you have posted the link to your youtube channel editor,
you need to post (share) the published, public, video link.

Chas
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Re: DIY polarization

#9 Post by Chas » Mon Jan 03, 2022 1:13 pm

There are all sorts of grades of complication ;-) .. there is no need to take the head off your microscope, if you dont want (but it is a sensible place for a filter to go..before the extra glass of the prism and the eyepiece).

Simplest; (if you have a dry mounted 'something'): One filter directly underneath the slide, or condenser and hold the other on top of the eyepiece .. look through and rotate this one.
Next: one filter directly under the slide, the other resting on top the slide.
-I am sure that you can muddle some variants together.
AND a bit of a health warning: I have not taken the angled head off your model/type of microscope, but 99% of the time when you release an angled-head, the prism is mounted into the top part and it has been perfectly safe to remove.

Also; 100+ years ago, the filters (polarising prisms, back then) were simply placed in the condenser mounting (with no condenser ) If you have something 'wet' you could drop out the condenser and simply rest the lower filter on top of the light ...
[They were often had to use weak light sources like oil lamps ...we have LEDS :-) :-) :-) ].

Hobbyst46
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Re: DIY polarization

#10 Post by Hobbyst46 » Mon Jan 03, 2022 1:49 pm

Also note, that if adding the polarizer seems to add weird small rings and ghosts and artefacts to the image, perhaps dust or scratches on the polarizer are the reason - when the polarizer is incorrectly placed in a plane that is simultaneously in focus as the specimen.
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

crb5
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Re: DIY polarization

#11 Post by crb5 » Mon Jan 03, 2022 5:00 pm

Sorry, I posted the wrong link - here is the one to access the polarization video https://www.youtube.com/watch?v=iNNkdHyvhbs - just need to skip the ad.

MichaelG.
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Re: DIY polarization

#12 Post by MichaelG. » Mon Jan 03, 2022 5:20 pm

crb5 wrote:
Mon Jan 03, 2022 5:00 pm
Sorry, I posted the wrong link - here is the one to access the polarization video https://www.youtube.com/watch?v=iNNkdHyvhbs - just need to skip the ad.
Much appreciated ... Thank You

MichaelG.
Too many 'projects'

Chas
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Re: DIY polarization

#13 Post by Chas » Mon Jan 03, 2022 10:36 pm

victhree, if you do pluck up the courage to take off the angled head, I think others will be interested to know what is underneath (mirror, prism?) :-)
..well I would be, if no-one else!
(It is also a good opportunity to see if these optics have a bit of fog).
Good luck with the polarisation .. some things show up more strikingly than others, if you have a ready made leaf section the heavier-walled 'pipework' can light up well.

SWmicro
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Re: DIY polarization

#14 Post by SWmicro » Mon Jan 03, 2022 11:58 pm

crb5 wrote:
Mon Jan 03, 2022 5:00 pm
Sorry, I posted the wrong link - here is the one to access the polarization video https://www.youtube.com/watch?v=iNNkdHyvhbs - just need to skip the ad.
Thanks, nice demo.

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victhree
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Re: DIY polarization

#15 Post by victhree » Tue Jan 04, 2022 5:48 am

crb5 wrote:
Mon Jan 03, 2022 5:00 pm
Sorry, I posted the wrong link - here is the one to access the polarization video https://www.youtube.com/watch?v=iNNkdHyvhbs - just need to skip the ad.
Brilliant, this covers pretty much all my questions. Thank you very much.

Chas
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Re: DIY polarization

#16 Post by Chas » Thu Jan 13, 2022 3:52 pm

A bit late in the day, this !
But I had read that cellophane .. the material that flowers etc are wrapped up in (and cellotape but that has the horrible gum on the back) works to somehow twist different colours, different amounts.
I thought one day when I go past the florists I will get some ..but I never went past the florists.
However on ebay there were 10 40x40cm sheets for £3..

Here is the effect on a section of unstained wood:

Crossed polarisers ...not very exciting:
XSC Unstained wood crossed polaroid.jpg
XSC Unstained wood crossed polaroid.jpg (79.89 KiB) Viewed 257 times


Uncross the filters a bit ... a little more colourfull..but not much:
XSC No cellophane not quite crossed polarisers.jpg
XSC No cellophane not quite crossed polarisers.jpg (107.47 KiB) Viewed 257 times


But one layer of this the cellophane over the understage polariser:
XSC cellophane effect one layer.jpg
XSC cellophane effect one layer.jpg (83.42 KiB) Viewed 257 times


And two layers :
XSC cellophane effect two layers i think.jpg
XSC cellophane effect two layers i think.jpg (108.35 KiB) Viewed 257 times

Just single shots, not stacked, Chinese condenserless scope.
( x10 objective)

The strapline is " Dont forget the cellophane, mum "
Last edited by Chas on Fri Jan 14, 2022 12:08 am, edited 1 time in total.

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josmann
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Re: DIY polarization

#17 Post by josmann » Thu Jan 13, 2022 6:16 pm

Chas wrote:
Thu Jan 13, 2022 3:52 pm
A bit late in the day, this !
But I had read that cellophane .. the material that flowers etc are wrapped up in (and cellotape but that has the horrible gum on the back) works to somehow twist different colours different amounts.
I thought one day when I go past the florists I will get some ..but I never went past the florists.
However on ebay there were 10 40x40cm sheets for £3..

Here is the effect on a section of unstained wood:
Very cool, Chas! I've been exploring polarization by plastics recently myself. It seems that the really tricky thing is to find plastic which doesn't elicit a strong polarization response! I have some craft plastic that I use for Rheinbergs (.020" 500 micron Craft Plastic by Grafix - it's on amazon) and it acts as almost a perfect visible spectrum half wave plate.

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Re: DIY polarization

#18 Post by BramHuntingNematodes » Thu Jan 13, 2022 7:58 pm

the film is acting as a wave retarder for some unknown portion of the waves. A Zeiss pol scope has an insert called the "Glimmer" which achieves this same effect over a more precisely known interval.
Last edited by BramHuntingNematodes on Fri Jan 14, 2022 12:12 am, edited 1 time in total.
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

Chas
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Re: DIY polarization

#19 Post by Chas » Fri Jan 14, 2022 12:03 am

Hi josmann.. I dont even begin to understand this polarisation stuff.. but (very roughly) are you making rheinberg filters that have different orientations of the film in different sectors?
(This cellophane looks to be around 0.02mm thick).

-Bram... Is glimmer a derivation of glamour, maybe ? ?

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Re: DIY polarization

#20 Post by BramHuntingNematodes » Fri Jan 14, 2022 12:11 am

I think it is German for mica, which is what wave retarders not made out of plastic film are made of.
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

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Re: DIY polarization

#21 Post by josmann » Fri Jan 14, 2022 8:43 am

Chas wrote:
Fri Jan 14, 2022 12:03 am
Hi josmann.. I dont even begin to understand this polarisation stuff.. but (very roughly) are you making rheinberg filters that have different orientations of the film in different sectors?
Well that's a real clever idea for an experiment! But I just bought it for regular Rheinbergs and happened to be playing with some sheets of polarizing film and some different stuff I had around the house.

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victhree
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Re: DIY polarization

#22 Post by victhree » Fri Jan 14, 2022 1:24 pm

I'm back, just wanted to post the results of the mod! Despite living in a city of 6M I somehow couldn't find any cheap solutions for polarization, so I ended up getting a small, 10 buck sheet of polarizing film from amazon. Since it's only 10x10 cm I'm treating it like it's the holy shroud. I've already allocated some parts of it for future experiments (i'm thinking rheinberg/patch stops of the stuff to make birefringent organelles POP without the dimming!)

Installation was stressful but everything went without a hitch. Upon removing the head, I found that there was a perfect spot for the analyser beneath the prism (thought this one had a mirror, the more you know!). The bottom filter required some arts and crafts to fit, but I made a cardboard ring that turns like a charm. I forgot to take pictures of the thing, oh well.

Without further ado, here are the results. Sorry for the quality, phone mount is still a bit crummy. What isn't crummy is the subject matter: as I zoomed into my latest pond sample to take a picture for this post, I caught a ciliate in the middle of division!!! It's the first time I've seen this in person, and I actually managed to film the moment of separation. I probably could've got a better image if it wasn't for the time constraint but holy cow! New profile picture anyone?

Image

Chas
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Re: DIY polarization

#23 Post by Chas » Fri Jan 14, 2022 9:40 pm

Definitely a nice new profile picture ! :-)

I have found some things out:
a]Even the thin (0.3mm) polarising film is sandwiched between protective layers.(I attacked it with some sandpaper !)

b] Sticky tape makes a good (stronger) twisting material than my cellophane sheets. Getting the same orientation of several layers, is easy too!

Here are several layerings of generic sticky tape on a microscope slide put between two crossed polarisers [my computer screen and a ~2"x 2"filter]:
sticky tape layers on microscope slide 640.jpg
sticky tape layers on microscope slide 640.jpg (43.8 KiB) Viewed 111 times
-One or two layers dont make for a vivid background colour (yellow and pale green) when the polarisers are crossed.

But when the polarisers are not crossed, but set to a straight-through orientation
One or two layers of tape do give a blue or vivid red colour:
Same slide but polariser turned to see through position 640.jpg
Same slide but polariser turned to see through position 640.jpg (45.89 KiB) Viewed 111 times

So if one places a filter of made of sticky tape over the bottom polariser, the two polarisers dont need, or perhaps want to be, set to completely blocked
Last edited by Chas on Sat Jan 15, 2022 9:09 am, edited 2 times in total.

Chas
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Re: DIY polarization

#24 Post by Chas » Sat Jan 15, 2022 8:48 am

This seems a helpful article :
https://charteredengineerspacific.ca/im ... oscopy.pdf

But I dont think that my modern generic tape is as powerful as the cellophane tape in this article [ 1974 ]... unless of course I still misunderstand ! :-) :-)!
EDIT: Yes I am wrong: The modern generic tape seems to be 'stronger' than the tape used in the 1974 article...the two layers of modern tape 'skip over' the red. [See next post].

Chas
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Re: DIY polarization

#25 Post by Chas » Sun Jan 16, 2022 11:22 am

Here is an interactive chart of the colours
for the tape between crossed polarisers:

https://micro.magnet.fsu.edu/primer/jav ... index.html


Moving the mouse pointer across the chart I come up with, very roughly (bearing in mind I might not have been holding the slide at 45 degrees, whitebalance et al.):
One layer ~ 370 ..First order Yellow
Two layers ~740..Second order Green
Three Layers ~1100..Second order Purple
Four Layers ~1480..Third order Red/Pink ish

So two layers of this tape go beyond the first order red and into the second order.

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