Getting micro-organisms in focus
using mouse-over images with different optical sections
by Bill Ells & Wim van Egmond


wait for the second image to load and move your mouse over the image to switch focus

Bill mentioned the problems of getting microscopic organisms with a distinct three dimensional shape in focus. When you observe these creatures under the microscope you can change your area of focus very easily by adjusting the height of the sample. This way you can get an idea of the actual 3D shape of the organism. The only way to capture this in images is by video or film.

There is one (more limited method), a simple trick I demonstrated in the article an Interactive Rotifer. This time I used the mouse-over trick to show 2 different optical sections through two freshwater algae. On the first page it was a desmid. I could show both the cell wall structure and the cell contents. On this page I photographed the common pond-scum Spirogyra. The first image shows the chloroplasts that run in a helix. When you move your mouse over the image we go deeper inside the cell. There the nucleus can be seen hanging between thin fibres.

Like Bill said, it is not always easy to get a good image of micro-organisms. There are some simple methods that might make observations easier. When you heat Vaseline it becomes fluid. With a small brush you can make a ring under the coverslip. This way the sample will not dry out and can be examined for hours (make sure the sample is not heated too much by the microscope's light). You can press the coverslip until the creature can't move. The spirogyra picture shows that the cell was pressed against the coverslip, just enough to get a larger area in focus without destroying the cell.

The shallow depth of field does have one advantage. By selective focussing you can point out certain features!

It is not difficult to make these mouse-over (or roll-over) images. You can copy part of the html from this page and change the names I gave to the images into the names of your own images. I made the backgrounds one even colour to make the images more alike.

Both pictures were made with the 40X objective and an Olympus 2.8X photo-eyepiece on a Zeiss standard microscope.

Page 3 shows some interesting features on Micrasterias papillifera!

Back to Page 1

Comments to the authors Comments to the author sent via our contacts page quoting page url plus : ('wells','')">Bill Ells & Comments to the author sent via our contacts page quoting page url plus : ('wegmond','')">Wim van Egmond are welcomed.

More pictures of micro-organisms can be found on Wim's HOME PAGE 

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All photographs Wim van Egmond

Published in the March 2001 edition of Micscape Magazine.

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