The Homemade Microscope by Roger Baker
A compelling piece that speculation that Leeuwenhoek must have invented a compound lens microscope and then he shows how he thinks it was done.
With permission from Science Probe April 1991.


An LED illuminator for reflected light microscopy and photomicroscopy

Roger C. Baker Jr., March 10, 2005.


led






















 On the left is a view of the "top" of my illuminatorr.  On the leftt is a veiw of the illuminotor it up and mounted on the 4x objective of my Chinese biological microscope;

This device was made to fit on my 4x and 10 x biological microscope planar microscope objectives, which are primarily designed to view slides. Accordingly, they have a relatively short focus and high numerical aperture. When the 4x objective is focused on an object, there is about 8 mm of clearance space.  

My LED illuminator resembles a removable cylindrical brass collar that clamps around the microscope objective. This collar bears four or more wooden fin-like LED supports. The LEDs are each wired in parallel with current limiting resistors via two semicircular copper wire connectors.

The collar was made from a strip of brass sold for hobbists (K&S Engineering, Chicago) .025” thick, an inch wide, and about 4.5” long. The strip width should be trimmed if necessary to slightly less than the flat  cylindrical length of the objective. The length of the brass strip should be such that it equals the circumference of the objective lens plus the length of two extended 5/8”  flanges used to tighten it.

The brass strip should be initially heated to a red heat with a propane torch to anneal and soften it. The two ends are then bent sharply upward in the same direction at a 90 degree angle. Finally, the strip is bent in the opposite  direction around a metal rod, with about the same diameter as the objective. I tapped the strip with a soft piece of wood so it conforms closely to the rod to make a nearly closed cylinder leaving the flanges extending outward and parallel to each other. The resulting shape should be such that there is some clearance around the objective until the extending flanges are squeezed together, causing the springy collar to tighten and grip the objective. Finally the flanges are clamped together and a dimple is made near to their edge with a nail set. A hole is drilled through the both of them them, allowing a nut and bolt to be inserted. These are used to tighten the collar onto the objective using mild finger pressure.

The white LEDs  I used have a beam spread of about 15 degrees, and are said to generate about 10 candellas apiece (RL5-W10015). Not including shipping, they cost $1.19 apiece from:      http://www.superbrightleds.com/leds.htm.

Chalky Limestone Slab
Here is an image of my illuminator showing a chalky limestone slab stained with  gentian violet (sometimes called crystal violet). The view is a  ground and stained fossil surface as seen at 40 power magnification.
The are a few artifacts; the light slash to one side is the reflective meniscus of the cover glass edge, there are a few bits of stray dust on the glass, etc. The rock sample is typical of Austin area sedimentary limestone, with a flower-like cross section of a fossil visible toward the bottom center of the image.

My Canon Powershot A-80 4 megapixel digital camera was held in direct contact with the rim of the wide glass binocular eyepiece and adjusted sideways until the image was nice and bright on the camera's LCD display.

I have not yet learned how to always attain the optimum focus, but the microscope optics theselves are capable of giving sharp images to the edges of the field assuming the surface is properly planar with respect to the objective lens axis. This is not necessarily the case with my hand sawed rock slabs.

A Previously Unpublished Limestone Micro-Fossil Staining Procedure
The surface of the rock is roughed out with coarser grinding methods and finally ground against glass with # 600 silicon carbide/water slurry. It is rinsed clean with fresh water. A few drops of a strong alcoholic solution of gentian violet dye is then spread across the surface with the help of the shaft of the eye dropper. It is then allowed to dry, giving the rock surface an iridescent green luster.

This dried stain is next rinsed off with several copious rinses of fresh water, without mechanical wiping although a hand-spray bottle can be used, to remove most of the non-absorbed stain. A drop of glycerine is then applied to the wet stained surface. Finally a cover glass placed on top of the glycerine to give an optically flat surface to view or photograph.

This staining procedure is capable of revealing visually interesting internal structures in many fossilized shell remains. These are subsequently visible as intensity variations of the adsorbed stain.

The nature of the gentian violet staining process at near neutral PH seems to depend  on the surface chemistry of the exposed material, and not merely the porosity of the mineral. That the atomic surface layer of an insoluble mineral can be stained is indicated to me by the fact that the glassy fractured grains of silicon carbide abrasive, which is a hard and chemically inert crystal, become stained and then look somewhat like flakes of purple confetti.