www.photomacrography.net :: View topic - To demostrate the principle of Phase Contrast?
www.photomacrography.net Forum Index
An online community dedicated to the practices of photomacrography, close-up and macro photography, and photomicrography.
Photomacrography Front Page Amateurmicrography Front Page
Old Forums/Galleries
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
To demostrate the principle of Phase Contrast?

 
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Beginners Micro
View previous topic :: View next topic  
Author Message
ChrisR
Site Admin


Joined: 14 Mar 2009
Posts: 7256
Location: Near London, UK

PostPosted: Sat Dec 03, 2016 11:32 am    Post subject: To demostrate the principle of Phase Contrast? Reply with quote

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
Back to top
View user's profile Send private message
JohnyM



Joined: 24 Dec 2013
Posts: 166

PostPosted: Sat Dec 03, 2016 11:58 am    Post subject: Reply with quote

I think cheek cells are excellent for this. Eazy to prepare, diff vs bf is huge.
Back to top
View user's profile Send private message
Pau
Site Admin


Joined: 20 Jan 2010
Posts: 4003
Location: Valencia, Spain

PostPosted: Sat Dec 03, 2016 12:17 pm    Post subject: Reply with quote

Chris, could you elaborate it?
_________________
Pau
Back to top
View user's profile Send private message
ChrisR
Site Admin


Joined: 14 Mar 2009
Posts: 7256
Location: Near London, UK

PostPosted: Sat Dec 03, 2016 3:37 pm    Post subject: Reply with quote

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 Smile
I could buy a phase condenser and objective (Oly CH) to show the result, rather than the HOW.
_________________
Chris R
Back to top
View user's profile Send private message
JohnyM



Joined: 24 Dec 2013
Posts: 166

PostPosted: Sat Dec 03, 2016 5:14 pm    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message
Pau
Site Admin


Joined: 20 Jan 2010
Posts: 4003
Location: Valencia, Spain

PostPosted: Sat Dec 03, 2016 5:35 pm    Post subject: Reply with quote

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
Back to top
View user's profile Send private message
ChrisR
Site Admin


Joined: 14 Mar 2009
Posts: 7256
Location: Near London, UK

PostPosted: Sat Dec 03, 2016 7:09 pm    Post subject: Reply with quote

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/phase-contrast/introduction-to-phase-contrast-microscopy
Interactive Tutorial - Specimen Optical Path Length Variations

really doesn't do its job well at all. Evil or Very Mad
_________________
Chris R
Back to top
View user's profile Send private message
Pau
Site Admin


Joined: 20 Jan 2010
Posts: 4003
Location: Valencia, Spain

PostPosted: Sun Dec 04, 2016 2:24 am    Post subject: Reply with quote

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
Back to top
View user's profile Send private message
ChrisR
Site Admin


Joined: 14 Mar 2009
Posts: 7256
Location: Near London, UK

PostPosted: Sun Dec 04, 2016 2:52 am    Post subject: Reply with quote

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
Back to top
View user's profile Send private message
ChrisR
Site Admin


Joined: 14 Mar 2009
Posts: 7256
Location: Near London, UK

PostPosted: Sun Dec 04, 2016 3:56 pm    Post subject: Reply with quote

Quote:
By the way it appears to me that Nikon's demonstration of phase shift:
https://www.microscopyu.com/techniques/phase-contrast/introduction-to-phase-contrast-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
Back to top
View user's profile Send private message
Pau
Site Admin


Joined: 20 Jan 2010
Posts: 4003
Location: Valencia, Spain

PostPosted: Mon Dec 05, 2016 9:27 am    Post subject: Reply with quote

Quote:
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
Back to top
View user's profile Send private message
ChrisR
Site Admin


Joined: 14 Mar 2009
Posts: 7256
Location: Near London, UK

PostPosted: Mon Dec 05, 2016 10:32 am    Post subject: Reply with quote

Thanks!
_________________
Chris R
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Beginners Micro All times are GMT - 7 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group