Video of oblique light testing on a dark background under a microscope using "darkfield patch"

[fdupre]

Hello everyone,

Here is a video of oblique light tests on a dark background under the microscope using a "darkfield patch" :
https://youtu.be/gJV5Z7wWuA0

Drop of culture broth water deposited on a glass slide, filmed with a Canon 1200D/Rebel T5 in full HD 1080p at 24 frames per second directly controlled on a PC with Canon EOS Utility 2 software.

- sequence 1: taken with the 10x objective without patch
- sequence 2: taken with the 10x objective with a 15 mm diameter central circle patch
- sequence 3: taken with the 10x objective without patch
- sequence 4: taken with the 10x objective with a 15 mm diameter central circle patch
- sequence 5: taken with the 10x objective with a 15 mm diameter central circle patch
- sequence 6: taken with the 10x objective with a 15 mm diameter central circle patch
- sequence 7: taken with the 10x objective with a 15 mm diameter central circle patch
- sequence 8: taken with the 10x objective with half moon patch
- sequence 9: taken with the 40x objective with half moon patch
- sequence 10: taken with the 40x objective with half moon patch
- sequence 11: taken with the 40x objective with half moon patch

Sincerely,
FRanck

[MichaelG.]

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Very nice demonstration !
… particularly [and predictably enough] at the low magnification.

Thanks for sharing it.

MichaelG.

[Roldorf]

Congratulations in getting it to work and by the way I have never been able to use a darkfield patch above 10x only ever turns out oblique. Never been able to get the correct diameter. Think I will have to buy the darkfield condensor.
https://www.bresser.de/Mikroskopie/Zube ... y-TFM.html

Alan

[richbart]

Pretty neat.

[woyjwjl]

Can you provide a configuration image? Did the darkfield patches be made by myself?

lei

[fdupre]

Hello everyone,

Thank you very much for your feedback

@ Roldorf / Alan : For the diameter of the central circle, I took 9mm and 15 mm then, whatever the diameter, I had to adjust the condenser by completely decentering it in order to have the oblique light closer to the subject .
I also played with the diaphragm of the condenser in order to have as black a background as possible without attenuating the oblique light too much.
Regarding the adjustment of the vertical position of the condenser in relation to the blade, it is as close as possible to the top but not completely. You also have to play around a bit with this setting.
In short, I adjust the lighting as well as possible with the eyepiece on the subject and then I focus on the digital SLR and fine-tune the settings which are also really not very far from the rendering with the eyepiece.

@woyjwjl : I didn't make the patches myself. I bought them on the internet.
Regarding the configuration, I put the patches in the filter holder which is at the entrance of the condenser:

porte filtre condenseur.jpg (58.62 KiB) Viewed 2201 times

pastilles_fond_noir_petit.jpg (61.52 KiB) Viewed 2201 times

Sincerely,
FRanck

[MichaelG.]

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This, from the recently mentioned book by B.O.Payne, is succinct:

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Microscope Design and Construction

B938D204-4FC0-4542-9990-3CD493E71C45.jpeg (245.54 KiB) Viewed 2182 times

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MichaelG.

[fdupre]

Hello Michael,

Thanks for the very interesting informations.

Quote :
"In cases where this is troublesome it is better to use a low power dark ground condenser of the catoptric type (Fig. 5-11) which is markedly superior in this respect."

If I understood correctly what is explained above, with this:
https://www.bresser.de/en/Microscopes-M ... y-TFM.html
could we get better results ?

Sincerely,
Frank

[MichaelG.]

Hello, Frank

The one you have linked is suitable for the higher powers.

I will post a link, later, to an old Leitz document which details both high and low power dark-field condensers.

MichaelG.
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It’s later now: http://microscope.database.free.fr/Acce ... oscopy.pdf

… and here’s the updated version: http://www.science-info.net/docs/leitz/ ... denser.pdf

[fdupre]

thank you very much Michael