Another phase contrast cheat?

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
Post Reply
Message
Author
Sauerkraut
Posts: 211
Joined: Tue Apr 16, 2019 2:07 am
Location: Oregon, USA

Another phase contrast cheat?

#1 Post by Sauerkraut » Mon Jul 29, 2019 2:37 pm

Has anyone tried this method? If so, what does the author mean when he says "Imagine a small opaque (black) disk attached in the middle of the objective lens..." (near top of second page)? Does the dot need to be in the middle of the objective lens or could it be at the top/readily accessible part of the objective?

http://www.staff.science.uu.nl/~hooft10 ... ntrast.pdf

Heather

MichaelG.
Posts: 3976
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Another phase contrast cheat?

#2 Post by MichaelG. » Mon Jul 29, 2019 3:36 pm

Sauerkraut wrote:Has anyone tried this method? If so, what does the author mean when he says "Imagine a small opaque (black) disk attached in the middle of the objective lens..." (near top of second page)? Does the dot need to be in the middle of the objective lens or could it be at the top/readily accessible part of the objective?

http://www.staff.science.uu.nl/~hooft10 ... ntrast.pdf

Heather
First; Thanks for the interesting link, Heather

I'm almost certain that the author simply means the disk to be concentric with the objective lens, and that he is contemplating a fairly simple objective, not a complex multi-element design.

MichaelG.
Too many 'projects'

Sauerkraut
Posts: 211
Joined: Tue Apr 16, 2019 2:07 am
Location: Oregon, USA

Re: Another phase contrast cheat?

#3 Post by Sauerkraut » Mon Jul 29, 2019 6:01 pm

Thank you for the clarification. I'll give this method a try.

billbillt
Posts: 2895
Joined: Mon Nov 10, 2014 10:01 pm

Re: Another phase contrast cheat?

#4 Post by billbillt » Mon Jul 29, 2019 6:13 pm

Hi Heather,

Thanks for the link!... It looks doable...

The Best
BillT

Hobbyst46
Posts: 4277
Joined: Mon Aug 21, 2017 9:02 pm

Re: Another phase contrast cheat?

#5 Post by Hobbyst46 » Mon Jul 29, 2019 6:15 pm

An interesting idea from a Physics Nobel Prize Laurate. Thanks for the link, Sauerkraut.
My understanding is that the dot or disk is to be placed on the rear glass surface of the objective.
On the other hand, I wonder how easy it is do actually make and attach that disk. Would have been nice to see a real-world example. My new unbranded 4X0.1 plan objective looks a good candidate... ;)

Sauerkraut
Posts: 211
Joined: Tue Apr 16, 2019 2:07 am
Location: Oregon, USA

Re: Another phase contrast cheat?

#6 Post by Sauerkraut » Mon Jul 29, 2019 8:02 pm

Hobbyst46,

For my first attempt I'm going to try placing dots of various sizes on plastic discs, made from salvaged plastic packaging. There would likely be some distortion from the plastic but it could be enough to prove concept without putting dots directly on the objective lens.

Sauerkraut
Posts: 211
Joined: Tue Apr 16, 2019 2:07 am
Location: Oregon, USA

Re: Another phase contrast cheat?

#7 Post by Sauerkraut » Tue Jul 30, 2019 2:53 pm

So far small dots have achieved no noticeable changes and larger dots have given very nice dark field. It's possible the dot needs to be directly on the lens or very close.

MichaelG.
Posts: 3976
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Another phase contrast cheat?

#8 Post by MichaelG. » Tue Jul 30, 2019 4:01 pm

Sauerkraut wrote:So far small dots have achieved no noticeable changes and larger dots have given very nice dark field. It's possible the dot needs to be directly on the lens or very close.
That appears to be what the author illustrated ... Although, of course, it's only a diagram not a scale drawing.

MichaelG.
Too many 'projects'

chrisimbee
Posts: 105
Joined: Fri Mar 19, 2021 5:34 pm

Re: Another phase contrast cheat?

#9 Post by chrisimbee » Mon Apr 05, 2021 9:50 am

hello;

i've tried the method and yes it works quite well but it wont give the top results you can get with a proper phase contrast kit but still : if you have a spare objectif you can just put a dot of dark blue or black marquer in the center of the back lens. When you observe protists they 'll appear a bit brighter then the backgroung and if you make a stop the proper diameter in the filter holder you can reinforce the contrast even more.

The black dot acts both as the 1/4 wave plate as its a vry thin layer of a quite transparent material and also attenuate the direct light (zero order) :most of the light diffracted by the objects ( protozoa in this case) passes through the whole lens surface of the objectiv (even through the center where the dot is) and will interfere with whats left of the zero order ( somewhat dimmed by the ink and phase modified by the thickness of the ink) and create some contrast.

Funnily enough though ; the protozo appears quite bright surrounded by a darker halo.


Chris

I still think the cheapest way to obtain good phase contrast is to buy a secondhand phase objective and make you own phase annulus to put into the filter holder of the condenser (i'm working on it).

Chris
microscope Olympus BH2-BHTU+epifluo RFC @ 470 nm
Zeiss neofluar x16Ph, x40Ph, x100 oilPh
LOMO Ph x10 X20 X40 X90oil
Olympus SPFl x2
Olympus SPx20, SPx40 SPx100
camera astro ZWO ASI 120MM (n&b) et ZWO ASI 120 MC (colour)
Nikon D3100

Post Reply