Rheinberg illumination for Foldscope

123 years ago Julius Rheinberg invented a variation of the darkfield microscope by adding color to it. Essentially it involved using various combinations of transparent colored papers set up in a way where diffracted light would be of one color and the direct light falling on the object of another. Typically annular rings are made with the annular ring of one color and the central stop of another. You can also make a multi-colored annular ring and get really fancy effects. Read more about those in the following links.



The foldscope can also be hacked for Rheinberg illumination and here is how you do it. First, you need transparent films of various colors. I bought mine on amazon, but I remember buying these as a kid at throwaway prices in India. Then you need a desk-lamp on which you can place these papers. Being lazy I didnt make annular rings but just cut them into rectangles. I am sure we can a make a variety of annular ring filters too. So here is how I set it up.

Rheinberg illumination for Foldscope

This kind of optical staining has a range of possibilities, but they work best for near transparent life like the optical staining of Amoeba proteus (one of my favorite microscopic organisms). See the next video.

The range of microscopic objects you can enhance by optical staining are left to one’s imagination. In fact I am doing this more than often for everything I see. Some excerpts follow of the organisms I plan to write about soon.

13 Comments Add yours

  1. Manu Prakash says:

    Love love love the creativity. Beautiful work Laks! The color schemes are incredible!

    People – let’s paint the world with beautiful colors. What are we waiting for!


  2. Manu Prakash says:

    Also; need I say – just in time for Holi!!


  3. laksiyer says:

    Yes we are not far from holi. These gel filters are really fun to play with.
    I am planning to replicate this interesting filter that gives a nomarksi like effect. It seems to be a combintion of dark field and oblique illumination. How might we engineer this for the foldscope?

  4. Mitali says:

    That amoeba looked gorgeous! Need to try this out!!! 😀

  5. laksiyer says:

    @mitali you must try this. Gel paper is easy to get from an art shop. Also available online.

  6. Manu Prakash says:

    On your note on combined olblique and dark field imaging – our trick of tilting the angle just the right amount to get “pseudo phase” like contrast does do the same effect.

    I think you know this one very well, but here is an old link https://microcosmos.foldscope.com/?p=16093

    I made several Rhenberg filters in the past using a laser cutter. But many of these other patterns don’t need that – just an exacto knife will do. I have my weekend planned out to play with ideas you presented here. Can’t stop thinking about how beautiful this is!!


  7. laksiyer says:

    Oh yes @Manu. Can’t wait to see what you will come up with.

  8. Akib says:

    Great! Can foldscope be used for phase contrast microscopy? ( I think it will be very hard to do so).

    1. laksiyer says:

      @Akib. You get what we call pseudo phase contrast, a mixture of dark field and angular illumination by playing with the tilt of the camera. Manu has a post above where he shows how to do it. It is very useful to improve contrast.

  9. Akib says:

    Can you get rheighnberg illumination by cutting a color dot sticker into half and putting it on the led of the magnifying glass?

  10. laksiyer says:

    Perhaps you can, but the dot sticker is best transparent.

  11. Krrissh Singh says:

    How can I find amoeba (where exactly can I find it like pond water or something like that)

    1. laksiyer says:

      Pond water. Soil. Take some hay infusion, add some soil and you will find some there. Amoebae are everywhere.

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