How to create Nomarski-like effects with simple filter techniques
by Wim van Egmond, The Netherlands
a filter made of black paper with a piece of coloured plastic in the center creates a combination of oblique and dark-field illumination with a touch of colour!
my earlier Micscape article about 'Easy
to make' contrast enhancement filters for the microscope I gave
several suggestions how to use colour filters to create interesting effects.
One of the most expensive microscopic illumination techniques is differential interference contrast (D.I.C. or Nomarski). For this type of illumination a set of polarized filters and expensive prisms is required. It is a contrast enhancing technique with some special characteristics. The main advantage of this technique is the fact that it gives a very good optical section of a subject. It does give an attractive image but it should be noted that a false idea of relief is given.
I recently found out a combination of oblique illumination with dark field illumination to imitate the 'high light' and shadow effect that we see in Nomarski. By using a dark coloured filter in the center it is possible to make coloured backgrounds to complete the Nomarski imitation.
The filter can be made out of black paper. The moon-shaped hole can be cut with a circle cutter. First with the needle of the cutter in the center. Than the cutter should be placed off center to cut the hole. The small opening in the center is perhaps too small to be made with a circle cutter. It can be pierced or cut with a small surgical knife. It does not have to be perfectly round. The filter in the center should be dark. It can be darkened with a black marker pen. I often use blue because it gives a suggestion of an aquatic environment. But it can be any colour, even the combination of two colours works well, giving a more Nomarski-like result!
These two images of fossil radiolaria and sponge spicules from Barbados show the slight differences between this filter technique and Nomarski. I don't remember which one was taken with the new filter set but I think the one with slightly more 3D effect is the Nomarski. Or was it the other one :-) .
All comments to the author Wim van Egmond are welcomed.
Visit Wims home page for links to his many web pages on microscopy
An Introduction to Microscopy
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