Polarization Contrast Lighting Technique

[Pat Thielen]

Howdy everyone!

I came across a video on YouTube where a representative of Motic was discussing polarization contrast using my model microscope (BA310). I realized that a little while ago someone here suggested I try polarization, which was what the video was about. So, I started thinking about it and found I could buy the polarization contrast kit by Motic for $90.00 at microscopeworld.com. However, they also said in the item description that it can't be sued with LED lighting, which is what I have.

So... Does anyone know if this is true -- That I can't use polarization contrast with my LED lighting? I assume it is, but I thought I'd run the question by the forums to see if anyone has any experience with it. Also, how good is this lighting for working with biological specimens?

Thanks much!

[zzffnn]

Pat,

My polarizer and analyzer work with my LED just fine. I got beautiful pol colors.

Pol may highlight muscle, fibrous or bone tissues of biological subjects. I would say it is fun to have, though may not be very useful (it is much more useful for minerals and crystals).

I am not sure why Motic said their kit won't work well with LED. I am guessing maybe because many LED have different spectrum distribution than a regular halogen? My LED lacks a major part of green color, for example. Polarization can be used to characterize crystals, so maybe such characterization process depend on certain light spectrum properties that LEDs do not have. Thus not good enough for scientific research. But good enough for my hobbyist use.

[mrsonchus]

Hi Pat, I use a home-made polarization setup on my SP200, which I converted to LED some time ago. It works perfectly well for me - examining permanently-mounted plant tissue for crystals therein. It works really well for showing raphides ('crystal 'rods) and especially druses (crystal 'flowers') within or between the cells; also the lignified cell-walls of vessels such as xylem will show beautifully with the polarizer.

Personally I see no problems with LED, but I'm not of course using it for a critically demanding purpose, just botanical sections, stained and/or unstained.

[billbillt]

I agree completely with John B.. Polarization is really simple to setup and use.. I place one filter over the light where I can easily rotate it, and one somewhere in the light train above the subject...

[mrsonchus]

Funnily enough I was looking at some crystals in the cells of an unplanted Daffodil bulb's root-tip section (LS) mounted last year (actually I made those slides to examine the cellular zones of the root-tip and mitotic stages).

The idea is that the tip cells (actually the 'root-cap' cells that protect the tip and slough-off continually as the root progresses in growth) contain tiny 'particles' that within each cell act like 'marbles in a jar' and settle towards gravity as the orientation of the root's tip may alter.
This mechanism enables Geotropic response of the root - enabling it to always 'know which way is down' and ensure by altering the rate of elongation of cells further back from the tip to allow one side to elongate more quickly than the other - effectively 'steering the root tip back to downwards' as it grows!

Anyway, looked at with brightfield these ('statoliths') are just ghostly outlines of "there's something in those cells" nature. Curiosity would never let me leave it there of course, so I moved over to my little phase contrast 'scope - "hmm crystals I think" being my next response to the deepening investigation (this is a great example of exactly why I love microscopy and Botany in particular - the mysteries never end, they just deepen...).

Looked at also through my improvised and very effective polarizer with my SP200 'scope they certainly were confirmed for my satisfaction to indeed be crystals, glowing with polarizers crossed to or close-to extinction...

The story didn't end there - I had since read that they were in fact not the usual and ubiquitous Calcium Oxalate variety found in so many plant tissues in differing crystaline forms (e.g. raphide needles, druse 'flowers') but in fact starch.
Well, this was supported by the fact that, as my brightfield images also showed, Lugol's Iodine did in fact stain these grains and indicate that they are likely to be starch - enough evidence you may think - you can never have too much information with Botanical microscopy!

Sooo, upon the acquisition of my 'Big O' Orthoplan, and recently bought Leitz polarizer filter disc/s for the light port - I used a camera polarizer filter over the light-port of my SP200 - (one end of the polarizer sandwich) side of the specimen, all that remained was to put my home-made analyzer side (made by cutting a 'tongue shaped' piece from plastic polarizing film bought online - note: - must be linear polarizer not circular) into the handy slot above the Orthoplan's nosepiece - thus fulfilling the requirement for polarized viewing.

Well, as I turned the lower polarizer ever closer to extinction and the image began to darken, out of the gloom came the expected brightly visible 'crystals' - only this time with a far superior image quality that - lo and behold - showed a beautifully clear 'Maltese cross' image of each crystal - definitely a strong sign of starch crystals!

The simple and very cheap (under £10) polarizer as made for my SP200 is a wonderful addition - forget the expensive but similarly basic kit and start with the camera polarizer (cost me £2 online) and a small sheet of film (cost about £6 online) - remember both must be linear.

Here's an image or two that pleased me greatly as soon as I spotted the 'Maltese crosses' - first time I'd seen these other than in other folks' images. I prefer the nearly-extinct version to the totally extinct 'starry night sky' version of these particular crystals...

Something's there....

ws_part2_x40_EH_root_phase.jpg (120.03 KiB) Viewed 5846 times

Polarizer at extinction - 'starry sky' image..

ws_polarizer-maltese-cross-.jpg (45.35 KiB) Viewed 5846 times

My favourite - part-extinction - lots of extra information to my eyes,

ws_polarized statoliths maltese cross.jpg (84.62 KiB) Viewed 5846 times

Sorry to ramble-on, just wanted to share the benefits I gained from the cheap and quick polarizing set-up..

[Crater Eddie]

Very cool John!
CE

[billbillt]

WONDERFUL!!... Beautiful photos... Your crystals show up nicely..

BillT

[Cyclops]

I have a couple of polarizers with a 30.5mm thread that a friend sent me years ago, I might try them with my new scope, tho fitting one above the subject could prove fun, unless I simply sit it on top of the eyepiece. But how well would pol work for say pond life? Regarding the pols I notice when screwed together if I simply hold them up and look through them and rotate I get an effect like a regular pol on a camera, reflections disappear and shiny objects appear matte. But if I do the same looking through the other way I see colours.

[Culicoides]

Pat, if you use a polarising filter or film over the light and one over the eyepiece make sure they are linear polarising (most pol filters for photography are circular polarised, and probable won't work.
John

[billbillt]

I agree with John.. They need to be linear polarized and not circular..

BillT