MicrobeHunter.com Microscopy Forum

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

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.

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

Hi Heather,

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

The Best
BillT

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...

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.

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.

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.

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