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Polarization (Olympus BH2-KP and crystals)
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NikonUser



Joined: 04 Sep 2008
Posts: 2534
Location: southern New Brunswick, Canada

PostPosted: Mon Oct 10, 2011 9:26 am    Post subject: Polarization (Olympus BH2-KP and crystals) Reply with quote

I just received an Olympus "Simple Polarizing Attachment - BH2-KP" that consists of an intermediate tube with a slide-in analyser, and a substage polarizer.
Image below is of a mixture of salicylic and lactic acids, DPlan 4x + 1.25x intermediate tube + 2.5x relay lens; flash
I was expecting pretty colours Sad

NU11123

Admin edit by request: moved and changed name. Was "What am I doing wrong?"
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NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
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Charles Krebs



Joined: 01 Aug 2006
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Location: Issaquah, WA USA

PostPosted: Mon Oct 10, 2011 11:37 am    Post subject: Reply with quote

NU,

Try some ascorbic acid and compare the results. I think you will find what you are looking for. (At least the crystal from the salicylic acid compound I recently posted showed relatively weak birefringence under simple crossed pols... needed "help" from the DIC).

You will also benefit by placing some "wave plates" (aka "retardation plates") somewhere in the path between the two polarizers. (If they are home-made and optically not that great it's best, and easy, to put it somewhere below the subject).

A good source for half-wave plate material is common cellophane (like the thin kind kind used to tightly wrap CDs and DVDs)


Search "cellophane wave plate" and you will get many hits like these:
http://news.cnet.com/Researcher-sees-cellophane-window-to-3D/2100-1044_3-5070510.html
http://rsi.aip.org/resource/1/rsinak/v74/i8/p3636_s1?isAuthorized=no

From the lower left of your image it appears that you are getting excellent "extinction". Be sure to play around varying the subject rotations and polarizer rotations.
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NikonUser



Joined: 04 Sep 2008
Posts: 2534
Location: southern New Brunswick, Canada

PostPosted: Mon Oct 10, 2011 1:07 pm    Post subject: Reply with quote

Thanks for this Charles.
I have an Olympus 530nm wave plate, somewhere in transit, that is designed to slide in a slot beneath the analyser in the intermediate tube; so I will try it out before 'playing' with cellophane.
Extinction is so good that when I tried to photograph an aquatic mite larva I could get nice glowing muscles only on an otherwise black image.
So dark that even my powerful Nikon flash at full power ended up more like moon light.

Can one use a combination of DIC and polarization on a BHS?

Will give ascorbic acid a try.
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NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

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NikonUser



Joined: 04 Sep 2008
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Location: southern New Brunswick, Canada

PostPosted: Wed Oct 12, 2011 1:20 pm    Post subject: Reply with quote

Charles. I could not find and Ascorbic Acid but had some Oxalic Acid:
HERE

Cellophane made the Salicylic Acid smear a little more colourful; the Oxalic Acid gave nice colours without a wave plate and without cellophane.
_________________
NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

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Olympus microscope and objectives
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Planapo



Joined: 07 Nov 2006
Posts: 1533
Location: Germany, in the United States of Europe

PostPosted: Thu Oct 13, 2011 7:02 am    Post subject: Reply with quote

As I mostly see these BH2-KP intermediate tubes offered with the slide-in analyzer, but without the original Oly substage polarizer:
What could one use instead? Would a polarizing photo filter, laid upon the light-outlet, work well?

--Betty
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NikonUser



Joined: 04 Sep 2008
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Location: southern New Brunswick, Canada

PostPosted: Thu Oct 13, 2011 8:13 am    Post subject: Reply with quote

I could have saved money Crying or Very sad

I just substituted my camera's polarizer - a B+W TOP-POL - for the Olympus.
Identical results with the oxalic acid smear.
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NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

Nikon camera, lenses and objectives
Olympus microscope and objectives
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Planapo



Joined: 07 Nov 2006
Posts: 1533
Location: Germany, in the United States of Europe

PostPosted: Thu Oct 13, 2011 9:11 am    Post subject: Reply with quote

Quote:
I could have saved money Sad

I'm sorry for that!

But
Quote:
I just substituted my camera's polarizer - a B+W TOP-POL - for the Olympus.
Identical results with the oxalic acid smear.


thanks for trying it out and the fast answer! Very Happy

--Betty
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Pau
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Joined: 20 Jan 2010
Posts: 4345
Location: Valencia, Spain

PostPosted: Thu Oct 13, 2011 9:40 am    Post subject: Reply with quote

NikonUser wrote:
What I am doing wrong?

Nothing Laughing
Not all crystals produce the same interference colors. In the middle of the Michel-Levy interference color chart the colors are more vivid (psycho ) and higher or lower order ones are weaker.
http://www.modernmicroscopy.com/main.asp?article=15&page=1
It's a consequence of the birrefingence, that varies as function of several factors, being the more important ones the crystalline structure, the thickness, crystal orientation and composition.

In fact, despite you was looking for vivid colors, I like more this picture than the oxalic acid one.
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Pau
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PostPosted: Thu Oct 13, 2011 9:52 am    Post subject: Reply with quote

Planapo wrote:
As I mostly see these BH2-KP intermediate tubes offered with the slide-in analyzer, but without the original Oly substage polarizer:
What could one use instead? Would a polarizing photo filter, laid upon the light-outlet, work well?
--Betty

Betty, it's a matter of test, not all camera filters are equally convenient. All will allow cross pol observations of crystals but tue quality of the colors and in special the black background rendering can vary a lot. Much of them induce strong color backgrounds (usually blue but can be red, purple...uneven..)while others are OK or with just a bit less black background)
If you have the filters try them, if not perhaps a good polarizing film would be a better inexpensive option: http://www.edmundoptics.com/products/displayproduct.cfm?productID=1912
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Planapo



Joined: 07 Nov 2006
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PostPosted: Thu Oct 13, 2011 2:15 pm    Post subject: Reply with quote

Pau, thanks for the additional info!

As I have only a circular polarizing filter, the sheet material you have linked to, seems a good option.
Moreover, from that I think I could cut out a little disc and use it as an insert in my condenser.

--Betty
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Chris S.
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PostPosted: Thu Oct 13, 2011 9:57 pm    Post subject: Reply with quote

The product that Pau suggested, Edmunds Optics Techspec "Visible Polarizing Laminated Film" is something I use regularly to polarize my lights, and it is excellent. I also have a cheaper polarizing film from another source, and the Techspec product is far better--in extinction, color neutrality, and ease of handling. With the Techspec product, the polarizing layer is laminated between sheets of cellulose triacetate, which give just the right amount of stiffness to make it easy to handle; the cheaper product kept coiling into a tube, which made it a nightmare to handle. On the downside, I am creating dark "burned" areas in the Techspec material--but am often shooting flash at full power, 1,000-1,500 times per stack, and even so, it takes a few such stacks to see degradation. There are probably ways to prevent this discoloration (separate the flash from the polarizing material a bit, add IR or perhaps UV blocking, etc), but I haven't bothered trying any--I just consider the material to be a consumable.

Edmund also sells a very nice high extinction polarizing filter mounted in glass, which I use behind my infinite objectives. It works very well, comparably to the Olympus analyzer that I use behind finite objectives. My B&W circular polarizer, used in this role, delivers considerably lower extinction--quite a different experience than NU had with his B&W Top-Pol. (By the way, does anyone know what "Top" means in this instance? It appears to be the designation B&W puts on their linear polarizers, but the literature I've looked at does not say why.)

--Chris
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Planapo



Joined: 07 Nov 2006
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Location: Germany, in the United States of Europe

PostPosted: Sat Oct 15, 2011 12:56 am    Post subject: Reply with quote

Chris, thanks for reporting on your experiences with the polarizing foils. So I will definitely go for the stiff laminated sheets that don't coil up, as for a cut-out little disk to insert into my condenser it has to be plane.

When you write that you use polarizing filters "behind objectives" does that mean they are installed between objective and bellows, or do you use a microscope with an intermediate tube then?

--Betty
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Chris S.
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PostPosted: Sat Oct 15, 2011 1:41 am    Post subject: Reply with quote

Planapo wrote:
When you write that you use polarizing filters "behind objectives" does that mean they are installed between objective and bellows, or do you use a microscope with an intermediate tube then?

Betty, I have two polarizers/mounts that go behind the objectives--one for finite objectives on the bellows, and one for infinite objectives on a tube lens. This tube lens is not in a microscope per se, but perhaps the Bratcam is beginning to resemble one. Since I come from a photography background and have little knowledge of microscopy, I originally thought of polarizing filters as something that we stuck on the front of lenses. I wondered why I could not find information on polarizing filters for microscope objectives. A question in this forum was answered very helpfully--that microscopists call polarizers used in the optical path "analyzers," and typically put them behind their objectives. Seems obvious now, but it was a surprise to me. And getting addition information was much easier, once I knew the correct search term.

In my finite system, the polarizer goes between objective and bellows. In my infinite system, the polarizer goes between objective and tube lens. Both my polarizing assemblies use hardware from Edmund Optics. In the finite system, the filter itself is an Olympus microscope analyzer. In the infinite system, the filter is a Edmund Techspec high extinction.

I don't want to hijack NU's thread by posting pictures, but the infinite polarizing assembly is documented here in images 5 and 6, counting from the top. I haven't documented the finite polarizing assembly (though it's on my to-do list), but if you look here , fourth image down, it goes between the cone-shaped adapter labeled "L," and the objective.

Not sure if these approaches are as good as it can get. They are working well for me, but I do have ideas for improvement. Stay tuned. . .or PM me if you want untested thoughts.

Does this anwer the question?

Cheers,

--Chris
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Planapo



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PostPosted: Sat Oct 15, 2011 7:13 am    Post subject: Reply with quote

Quote:
Does this anwer the question?

Yes, Sir!
Thanks for the answer.

--Betty
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Charles Krebs



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PostPosted: Sat Oct 15, 2011 7:42 am    Post subject: Reply with quote

Betty,

Don't forget... if you have the "universal" condenser with a rotatable polariser built in, you can use that for the lower polarizer for cross-polarized shots. I always use the one in the BH2-UCD for that purpose.
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