Darkfield Microscopy... is it that easy?

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ojd01
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Joined: Sun Nov 15, 2020 10:56 am
Location: Teesside, Middlesbrough, UK

Darkfield Microscopy... is it that easy?

Post by ojd01 »

Hello everyone!

Once again I am suffering from the problem of reading too much into a topic and getting confused. I have a "Radical" (Chinese brand I think) compound trinocular microscope with a standard brightfield condenser. I also have some 3D printed darkfield filters I purchased from eBay.

Is it as easy as sorting your illumination and sticking a filter before the condenser? If there any any resources, articles anyone recommends in particular, that would be amazing!

My microscope has the little attachment slot for the 3D printed filters. I am learning these techniques one-by-one and having great fun! I think the holder is 32mm diameter.

P.S. I am hoping to upgrade to an Olympus BH2 or similar in the future. Just stuck with this microscope for now :)
Instagram: @ojd_photo

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Alan Wood
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Re: Darkfield Microscopy... is it that easy?

Post by Alan Wood »

Yes, it really is that easy. Just put a dark-ground stop in the filter tray of the condenser, with the condenser iris diaphragm wide open.

You will need to experiment to find the best size stop for each objective. Too small and direct light will spoil the effect. Too big and not enough light will get around the edges of the stop, causing a dim image.

You can probably find one size that works o.k. with 4×, 10×, 20× and 40× objectives.

Do not expect to get good results with objectives over 40×.

Alan Wood

Ichthyophthirius
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Re: Darkfield Microscopy... is it that easy?

Post by Ichthyophthirius »

ojd01 wrote:
Thu Apr 15, 2021 6:23 am
Is it as easy as sorting your illumination and sticking a filter before the condenser?
Yes, for anything up to the 40:1 objective. The 10 - 40 range is probably the most rewarding with a simple condenser stop. You can also do oblique illumination in that range. A bright LED illumination is an advantage.

The specialised darkfield condensers (which often have to be used with oil illumination) are really meant for the 40 - 100 range, where a bright, high NA light cone is required. That shouldn't deter you from making your own filters for the low magnifications first!

https://www.olympus-lifescience.com/en/ ... darkfield/
https://www.future-science.com/doi/pdf/ ... /02324bi01

One thing that is important is the sample preparation. The sample should be as thin as possible for best results.

Good luck, Ichty

Beatsy
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Re: Darkfield Microscopy... is it that easy?

Post by Beatsy »

Yep, except for high NA objectives as noted by others. You need a darkfield condenser oiled to the slide for anything >NA0.95. I used to have a Zeiss NA1.4 DF condenser, but I lost it in a move (I think).

But losing the proper tool for the job led me to discover that simply shining a bright torch or similar onto the specimen from the side can work surprisingly well at all magnifications. It does with diatoms, anyway. Just needs careful aiming to avoid directing any light straight into the objective.

ojd01
Posts: 49
Joined: Sun Nov 15, 2020 10:56 am
Location: Teesside, Middlesbrough, UK

Re: Darkfield Microscopy... is it that easy?

Post by ojd01 »

Hey Beatsy, Alan and Ichty,

Thank you all for your amazing advice as always! I will give some DF stuff a go with my <10x objectives first!

Best Regards

Owen
Instagram: @ojd_photo

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