DIY polarizing

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Maryfox
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DIY polarizing

#1 Post by Maryfox » Tue Feb 26, 2019 8:59 pm

I finally learned about polarizing film. My budget student microscope doesn’t have any place to put normal polarizing filters. My ‘net searches took me to a clever device, (pic above) but the site referenced in the article no longer exists. The article was written in 1998 so that’s not a surprise Is anyone familiar with this or something similar? I ended up buying inexpensive film and it’s OK but there are minute scratches and artifacts that sometimes show up. My current solution is to cut a strip of film and tape it to the stage, then use another strip on top of the slide. I’ve just ordered acrylic polarizing filters from American Polarizers Inc hoping there’s be no scratches, etc.
Does anyone have a better solution than what I’m doing now
Clever polarizing device
Clever polarizing device
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My scope
My scope
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75RR
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Re: DIY polarizing

#2 Post by 75RR » Tue Feb 26, 2019 9:47 pm

Lift the head of your microscope and put the analyzer there (make sure it lies flat), then place a polarizer over the field diaphragm housing/ light port as shown in the image.
The analyzer and the polarizer are or can be the same. The different names denote their position on the microscope.
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mrsonchus
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Re: DIY polarizing

#3 Post by mrsonchus » Tue Feb 26, 2019 9:48 pm

Hi, for starters the polarising film needs to be of the 'linear' type not the 'circular' type - they look the same but the linear needs to be used.
I would place the piece below the slide resting on the light-source port, where it may be turned to whatever degree of extinction you like. The upper piece doesn't need to be turned, and is usually positioned above the objective but below the eyepiece....

Remember first, Linear polarising film not circular. For the lower polariser I use a camera-lens screw-on (the type that just screw onto the front of a camera lens) polarising filter simply placed onto the light-port and rotated as required.

There are many threads covering this subject in this forum, you may like to make a search for this topic also, within this forum that is.

John B.
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billbillt
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Re: DIY polarizing

#4 Post by billbillt » Tue Feb 26, 2019 9:53 pm

Hi Mary,

The idea is to have one between the light and the subject and another between the subject and the eye.. I use a second hand camera filter over the light so it is easy to rotate to get extinction.. This works also:

https://www.ebay.com/itm/Polarizing-Fil ... 2617982312

BillT

Hobbyst46
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Re: DIY polarizing

#5 Post by Hobbyst46 » Tue Feb 26, 2019 9:54 pm

The proper place for the top polarizer is not between the slide and objective, but between the objective and the sensor. That means, that you can place it on top of the eyepiece, or on/in the bottom end of the eyepiece (taking precautions that it does not glide down inside), or - where I think the best place - between the head and the stand. From the pic of your scope, the head is removable. So, remove the head, find a way to safely place a thin polarizer film circle in the space between the bottom of the head and the receptacle in the stand, then return the head.

Likewise, the proper place for the bottom polarizer, in this cae it will be the analyzer, is freely on top of the illumination port of the stage, directly below the condenser. This way, you can easily rotate it, and get the beautiful color patterns from birefringent specimends on the slides.

Such arrangement works nicely for me and other microscopists. The only downside is a slight loss of brightness, because the top polarizer is there all the time, and it blocks and reflects some light, but if the light source is bright, that is no big deal.

Edit: seems that several forum members responded simultaneously - so my suggestion only repeats others... ;)
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PeteM
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Re: DIY polarizing

#6 Post by PeteM » Tue Feb 26, 2019 10:26 pm

It's possible to buy inexpensive Chinese camera lens polarizers (say, $5 each) on Ebay. These will typically be flat, scratch free, glass mounted in a threaded filter mount. Ideally you'll get a linear polarizer but most circular polarizers can be flipped one way or the other to give the linear effect you want (inverse from the way the light would pass if on a camera).

So, if you measure the diameter of your bottom field area, you can typically find a camera polarizer that will fit in or over it -- and be easy to rotate. Cheap adapter rings can also help you get the right size or raise it up a bit.

You might be limited to cutting a piece of the linear film to fit over the objective turret and under the head (hopefully there's room) -- but there are also very small diameter polarizers meant for cell phone cameras. Some of these have very small diameters and will fit.

I've found the cheap polarizers better than the typical film for casual use. They don't have the full extinction (99.99% of light blocked when crossed) of better quality linear camera or microscope polarizers, but are a relative bargain.

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Maryfox
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Re: DIY polarizing

#7 Post by Maryfox » Thu Feb 28, 2019 1:32 pm

Thanks for your suggestions and especially for the quick responses. This is a very impressive forum on a truly great website. Most of what I've learned so far has come from this site and forum. I visit several other topic specific sites and a big difference is that everyone here is helpful, and not condescending to a newcomer. Many thanks.

BTW my light source is domed not flat precluding placing a filter directly on it. I'll use your suggestions to get it done. (Until my next problem) My 'net searches have taught me that I want linear polarization. Onward and upward.

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Re: DIY polarizing

#8 Post by Hobbyst46 » Thu Feb 28, 2019 2:55 pm

Indeed, you need linear polarizers. Please note, the optical plastic pieces in 3D movie spectacles are circular polarizers, not linear.
I suggest that, when you get the polarizing film, cut a circular piece, and place it "inside" the top of the illumination port, flat on top of the glass, whether the latter is planar or concave/convex. The polarizer can touch the glass, no problem. Where the red arrow points at.
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ChrisR
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Re: DIY polarizing

#9 Post by ChrisR » Fri Mar 01, 2019 12:32 am

You can use circular pol filters as long as you can choose which way round they go. Then it makes no difference.

You can tell what you've got, by using a mirror:

Watch carefully - it's quick!
https://www.youtube.com/watch?v=6lVIo9C0NDA

A circular pol filter is just a linear pol with a quarter wave plate on one side - the one which goes to the camera normally.
The qwp makes the polarization rotate, like a corkscrew as the wave travels, by making the electromagnetic wave out of phase with the electric field by 90º. The mirror reverses the direction of the rotation so when the light gets back to the filter it's blocked - the electric and electromagnetic waves are then 180º out of phase, and the plane of rotation is rotated by 90º.

If you have the qwp towards your eye instead of towards the mirror, the mirror gets plane pol light which it reflects in the same plane, so it's like you're looking through two linear pol filters which are not crossed - just the expected couple of stops dimmed.

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Re: DIY polarizing

#10 Post by Hobbyst46 » Sat Mar 02, 2019 12:36 pm

Creative and business minded people around the globe identify current needs or "vacuum" and rush to fill it with solutions.
Here is an entry from eBay for a set of "DIY" polarization kit for simple microscopes:
https://www.ebay.com/itm/Microscope-32- ... ctupt=true
(I am not related to them in any way).
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Maryfox
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Re: DIY polarizing

#11 Post by Maryfox » Sat Mar 02, 2019 4:26 pm

Linear My web searches have taken me to diagrams describing circular. Not for me. Nor do I want to think about wavelength ranges, retarders (whatever they do), etc. At this stage of my life (retired) I'm looking for simple, not necessarily easy, but simple. I'm waiting for my round (not circular) linear acrylic lenses to arrive.

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75RR
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Re: DIY polarizing

#12 Post by 75RR » Sat Mar 02, 2019 6:38 pm

Maryfox wrote:Linear My web searches have taken me to diagrams describing circular. Not for me. Nor do I want to think about wavelength ranges, retarders (whatever they do), etc. At this stage of my life (retired) I'm looking for simple, not necessarily easy, but simple. I'm waiting for my round (not circular) linear acrylic lenses to arrive.
There does seem to have been a somewhat overenthusiastic response to your question that has managed to obfuscate things a bit. ;)

Linear polarizers is the way to go.

Keeping it simple is my motto as well.
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mrsonchus
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Re: DIY polarizing

#13 Post by mrsonchus » Sat Mar 02, 2019 7:24 pm

Agree with you 100% 75' - it's really easy to get lost in technical detail in this hobby. I very often find that a step back and consideration of just what 'is going on' suggests a simple solution to start with at the very least.

John B. :)
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MichaelG.
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Re: DIY polarizing

#14 Post by MichaelG. » Sat Mar 02, 2019 7:26 pm

Maryfox wrote: At this stage of my life (retired) I'm looking for simple, not necessarily easy, but simple. I'm waiting for my round (not circular) linear acrylic lenses to arrive.
Whilst you are waiting: May I recommend this document, from Micscape:
http://www.microscopy-uk.org.uk/mag/ind ... eopol.html
The quoted prices are, of course, ludicrous ... but the simplicity, and effectiveness, of the device should be immediately apparent.

MichaelG.
Too many 'projects'

PeteM
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Re: DIY polarizing

#15 Post by PeteM » Sat Mar 02, 2019 8:06 pm

As noted above, a circular polarizer IS a linear polarizer when light passes the opposite way from its intended use on a camera.

The advantage here is that circular polarizers, complete with metal rings and threads, are now available for a few bucks each. They will be flatter and more scratch resistant than plastic polarizers cut to shape. They will also be more durable and easier to rotate, complete with that aluminum mounting ring.

Sure it's better to buy a linear polarizer if it is available -- and especially one from a name brand maker which will likely go to fuller extinction. I'll buy those whenever they are available in the size needed and not too many $$$.

Still, the cheap circular polarizers (a few bucks on Ebay, shipped from China) will do better, in my experience, than the typical linear polarizing film commonly sold -- or even the polarizers now being laser cut from plastic sheet and mounted in aluminum rings for microscopes by an Ebay seller for near 10x the price. Some of these end up domed and cause some slight optical problems.

For the OP -- if you measure the inside and/or outside diameter of your lamp housing, chances are you can find a combination of extensions or filter ring adapters that will work either inside or outside the mounting ring. Perhaps post a picture of your microscope with diameters measured (best in mm, since filters are measured that way). I've found affordable polarizers from around 16mm (cell phone camera) to 72mm (that one on a camera) with sizes a few mm apart all the way between.

Having outfitted dozens of scopes for kids and, while benefitting from a large filter/adapter scrap bin, I have always been able to find some combination that would fit over even a domed field lens. I'll use the plastic film to quickly help a kid with whatever scope they have, but don't consider it a long term solution.

Mounting a polarizer above the objective can be a little trickier. There's usually room under the head for a glass/ mounted polarizer (analyzer) -- as shown by 75Rr's diagram -- perhaps removed from its ring. Failing that a cut-to-fit bit of plastic will do. Failing even that, the polarizer can be mounted above an eyepiece.

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Re: DIY polarizing

#16 Post by PeteM » Sat Mar 02, 2019 8:32 pm

Just as a heads up on another field lens polarizer option, there is this:

https://www.ebay.com/itm/LOMO-MULTISCOP ... ctupt=true

It's a proper linear polarizer, with good extinction (better than most film or cheap camera polarizers, not quite as good as Nikon or Olympus high end scope polarizers costing 10x used).

It will clear a slightly domed lens and will fit OVER a 39mm feature or INSIDE a 43mm cavity (works OK on most Olympus BHS, BH2 series, for example). The polarizer itself is mounted in a 33+mm ring, which can be carefully separated from the the rest by sawing or turning.

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Re: DIY polarizing

#17 Post by ChrisR » Sat Mar 02, 2019 11:35 pm

The advantage here is that circular polarizers, complete with metal rings and threads, are now available for a few bucks each.
Exactly. Bottom line, use whatever you have or can get in good enough quality, cheapest. If it turns out to be a circular polarizer, which you can check for free in a mirror, just use it the right way round.
I don't think that's overcomplicating it!

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Maryfox
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Re: DIY polarizing

#18 Post by Maryfox » Tue Mar 05, 2019 1:46 pm

So I finally watched Oliver Kim's video "Crystals made with fire under the microscope" Should have done before my original post. :)

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75RR
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Re: DIY polarizing

#19 Post by 75RR » Tue Mar 05, 2019 7:01 pm

"Crystals made with fire under the microscope"
Great title and neat idea. Nevertheless, placing the analyzer under the head and the polarizer on top of the field housing/light port remains a more functional solution for sustained viewing.
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billbillt
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Re: DIY polarizing

#20 Post by billbillt » Sun Mar 10, 2019 1:27 pm

Here is more on polarizing microscopes.. This person did it the easy way and it works.. No need to spend much money on it..

https://microscopetalk.wordpress.com/pr ... icroscope/

BillT

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Maryfox
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Re: DIY polarizing

#21 Post by Maryfox » Sun Mar 10, 2019 6:23 pm

Thanks, BillT. Interesting blog - too bad it died.
Mary

billbillt
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Re: DIY polarizing

#22 Post by billbillt » Sun Mar 10, 2019 8:07 pm

Hi Mary,

Did you check out the rest of his site?.. He has a page on using home products for staining which I found interesting...

The Best,
BillT

Culicoides
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Re: DIY polarizing

#23 Post by Culicoides » Tue Mar 12, 2019 12:17 pm

I can understand linear polarisation, where the light is in one plane, but what is circular? Spiral, or concentric??
John B, Guildford, Sy.

billbillt
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Re: DIY polarizing

#24 Post by billbillt » Tue Mar 12, 2019 3:10 pm

Culicoides wrote:I can understand linear polarisation, where the light is in one plane, but what is circular? Spiral, or concentric??
John B, Guildford, Sy.
"Circular Polarizers are actually made up of a piece of high quality optical glass followed by a linear polarizing film, this film, which is actually a micro screen, filters out the scatters light rays and only passes light moving in one linear direction. Modern camera meters and auto focus systems can have problems reading light moving linearly is a quarter wave plate is added behind the polarizing film to send the light into the lens in a circular pattern. "

"A circular polarizer filter only allows light rays that are traveling in one direction to enter the lens. ... That is how the circular polarizer darkens blue skies, it reduces the amount of light coming from the sky into the camera. That is why when a circular polarizer is rotated the shutter speed or aperture will change"

"With a circular pol, the quarter wave plate on the rear of the polarizer spins the light before it enters the camera lens so that it doesn't get cross polarized on any reflective surfaces in the system, such as the partial mirror in a video tap or a DSLR mirror."

This is about it from Google... A lot of other pages but redundant...

BillT

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Re: DIY polarizing

#25 Post by Scarodactyl » Thu Mar 14, 2019 9:23 pm

The wikipedia article is a bit more specific about the optical phenomenon as well https://en.m.wikipedia.org/wiki/Circular_polarization
Basically it is rotating within the plane as it travels along, which traces a helix.

Culicoides
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Re: DIY polarizing

#26 Post by Culicoides » Thu Mar 14, 2019 10:50 pm

Many thanks for the explanation.
Now I begin to understand!

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