To demostrate the principle of Phase Contrast?

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ChrisR
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To demostrate the principle of Phase Contrast?

Post by ChrisR »

What can I use, to explain how the method works?

I can show materials which are polarising, or birefringent or fluorescent, but can't think what would demonstrate a property which enables "phase" to be used for contrast enhancement in microscopy.

Ideas?
Chris R

JohnyM
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Post by JohnyM »

I think cheek cells are excellent for this. Eazy to prepare, diff vs bf is huge.

Pau
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Post by Pau »

Chris, could you elaborate it?
Pau

ChrisR
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Post by ChrisR »

The school doesn't have anything but basic microscopes. I have Pol but that's all. I can explain how some microscopy techniques work from pictures, and rocks, filters and so on.
For example polarized light is easy to talk about with a skipping rope and some filters, DIC starts with birefringence, ie a big lump of calcite.
Fluor takes a UV lamp and some rocks.
Some of that's even pretty, which helps.

But how can I show "how phase contrast works" with physical lumps of things?

Cheek cells would be a good specimen, they all have those :)
I could buy a phase condenser and objective (Oly CH) to show the result, rather than the HOW.
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JohnyM
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Post by JohnyM »

That's a good idea. You can print condenser diaphragm pattern to save some bucks.
I dont think you can show phase contrast on anyhing else, because human eye doesnt detect phase subjects. PC is a converter - from phase, to contrast detection. It works on exact same physic laws as DIC acutally, as it is causing an interference between wavefronts.
Maybe, you can actually reproduce it in different scale. Phase ring can be made with soot, so if you got some old lenses and dia macro setup, maybe you can do "macro pc"... im actually gonna try to do that with old helios44 lens.

Pau
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Post by Pau »

When I was teaching a small Microscopy course (now unfortunately gone) I explained the principle with a power point with images mostly taken from Microscoyu, I'm pretty sure that most students didn't understand it because the lack of Physics background.
But having former experience with dark field (they made the condenser stops...) and comparing images from different techniques they had at least some idea of the practical aspects of the technique.
I also brought my personal phase microscope to the school so they could actually see the components and compare the image of the same samples (of course cheek cells between them) with DF and BF.

If the school physics lab has a wave cuvette the phenomenon of interference can be easily visualized, although translating it to the microscope is not obvious.
Pau

ChrisR
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Post by ChrisR »

What's a "wave cuvette" - it could be lost in translation. Is that something with "Young's slits"?



By the way it appears to me that Nikon's demonstration of phase shift:
https://www.microscopyu.com/techniques/ ... microscopy
Interactive Tutorial - Specimen Optical Path Length Variations

really doesn't do its job well at all. :evil:
Chris R

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Post by Pau »

wave cuvette....wrong translation from spanish cubeta de ondas, sorry

I think the adequate term is ripple tank, see for example https://www.youtube.com/watch?v=by7_TGZTZ_o
Pau

ChrisR
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Post by ChrisR »

Ah yes, I remember those from school days!

I'm trying to think of something using light waves.. Perhaps there's a demonstration based around a slide (dia) projector, or an overhead projector, using partial sheets of "wave plate".
Someone will have already done anything I can dream up.


I'm questioning my own understanding too of course.** EG, when the thoughts return from oil-on-water interference to a phase contrast image, why aren't colours more obvious?


** that curse and joy of teaching!
Chris R

ChrisR
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Post by ChrisR »

By the way it appears to me that Nikon's demonstration of phase shift:
https://www.microscopyu.com/techniques/ ... microscopy
Interactive Tutorial - Specimen Optical Path Length Variations

really doesn't do its job well at all.
Can anyone get this demo working? I can't!
ie:
discover how two specimens can have different combinations of these variables but still display the same path length.

I can only get the waves in phase with identical RIs and thicknesses.


Can someone help with this - some illustrations of phase 'scope configurations show a wave plate at the condenser, some don't. I was looking at a system whch used a ring of LEDs instead of a condenser annulus, which had no wave plate, I'm fairly sure.

If I were to put together demo image forming device, what could I use to demonstrate the action of the Phase ring at the ojective?
Chris R

Pau
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Post by Pau »

Can anyone get this demo working? I can't!
ie:
discover how two specimens can have different combinations of these variables but still display the same path length.

I can only get the waves in phase with identical RIs and thicknesses.
No, there must be a bug: the phase changes inside thr specimens but exits in phase at any setting, not useful to demonstrate anything
Pau

ChrisR
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Post by ChrisR »

Thanks!
Chris R

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