To the Fun Science Gallery Contents

 

Let's Build a
STEREO-ZOOM MICROSCOPE

Giorgio Carboni, August 2001
Translation edited by Joe Della-Fera

 


Stereo-Zoom Microscope

 

CONTENTS
INTRODUCTION
OPTICAL SCHEME
CHARACTERISTICS OF THIS MODEL
CONSTRUCTION
PARTS OF THE MICROSCOPE
PEDESTAL AND COLUMN
FOCUSING DEVICE
MATERIALS
INTRODUCTION
INTERMEDIATE PLATE
CARRIAGE
FOCUSING DEVICE
ANTI-ROTATION COLUMN
SETTING THE TENSION OF THE CABLES
SETTING THE BRAKE ON THE FOCUSING SHAFT
SETTING THE POSITION OF THE INTERMEDIATE PLATE
LINKAGE TUBE
OPTICAL ASSEMBLY
MATERIALS
INTRODUCTION
INTERNAL PRISMS
EXTERNAL PRISMS
ADJUSTING THE MOVEMENT OF THE SLIDES
ASSEMBLING AND ALIGNING THE PRISMS
BLACKENING OF INTERNAL PARTS
MOUNTING THE BINOCULARS
CHOICE AND MOUNTING OF THE OBJECTIVE
MATERIALS
MAGNIFICATION OF THE MICROSCOPE
CHOICE OF THE OBJECTIVE
MOUNTING THE OBJECTIVE
FINISHING
APPLICATION OF THE PLUGS
TRANSPARENT PEDESTAL
BOX AND BELL
USE OF THE MICROSCOPE
ADJUSTMENTS
SUPPORTING PLANE
ILLUMINATION
ACCESSORIES
MAINTENANCE
OBSERVATIONS
CONCLUSION
SOURCES OF PARTS
BIBLIOGRAPHY

INTRODUCTION

A stereo-zoom microscope is a stereoscopic microscope in which the variation of magnification is continuous. What is the main advantage of such an instrument? It is to be able to adjust the magnification to suit yourself. Obviously, you can do it only within the range of the available magnifications. Moreover, you can pass gradually from one magnification to another, without losing sight of the sample. However, what makes this type of instrument astounding is that increasing the magnification will make it appear as though you are diving into the sample. The first time you do this, it will take your breath away.

This project allows you to fabricate, with your own hands, a high quality stereo-zoom microscope, an instrument very useful for observing natural samples. As a bonus, it will serve to instill in young people, as well as adults, an interest in biology. The cost of this instrument is very low. But that is not the only reason to build it, in fact you can also find pleasure in doing mechanical and optical constructions. As we have said with regard to the normal stereoscopic microscope already described in this gallery, the construction of this instrument is good training to practice your own mechanical capabilities; it can also be an opportunity to acquire them. A technical school can use this article as the basis for a construction project to be carried out by the students, with the advantage of leaving to each student an instrument very useful for their education and their studies. Finally, to show to your friends a stereoscopic microscope, what's more provided with a zoom, made by your own hands, is something of which you will be proud.

 

OPTICAL SCHEME

The basic idea of this microscope is simple. After having build the stereoscopic microscope with a common objective, we asked ourselves: "What about using a camera zoom as an objective? Could we obtain a zoom stereoscopic microscope?". The answer which we have gotten from the construction of this instrument has been affirmative, but let us to have a closer look at how this microscope works.

Do you know that the stereoscopic microscopes allow us to see the samples in relief (in three dimensions)? To do this, it is necessary that each of our eyes sees the object from a slightly different angle. Many stereomicroscopes are made up of two separated microscopes which are kept aligned to observe the same point from two distinct angles. As with the normal stereoscopic microscope which we have already described in this gallery, this one is a common objective model. That is to say that the light bundle which gives origin to the two light bundles seen by the eyes passes through the same objective. Four prisms placed between the common objective and the binoculars split the original bundle into two equal parts and direct them to the objectives of the binoculars.

Binoculars are made to observe distant objects, and the light from the object which enters into the objective lens is practically parallel. Each objective of the binoculars forms an image at its focal distance, in a plane suitable to be observed and magnified by the eyepiece. As shown in Figure 2, the common objective is placed at its focal distance from the sample, so the light which emerges from this objective is parallel, as if the object was placed at infinity. As a consequence, the objectives of the binoculars will focus the separate images of the sample in the focal planes of their eyepieces. As usual, the eyepieces will magnify the image and will supply it to the observer.

Schema ottico


CHARACTERISTICS OF THIS MODEL

The optical scheme of this instrument does not show anything radically different compared to the stereoscopic microscope we have already described. The main difference is that, instead of using an objective with a fixed focal length, we will use an objective with a variable focal length, in practice a common zoom lens for a photographic camera. Unfortunately, these objectives have a rather small useful hole (aperture) for the passage of the light, of about ten millimeters in diameter. This forces us to modify the system of adjusting the interpupillary distance. To keep the two optical paths inside the aperture of the zoom, the external prisms must follow the movement of the objectives of the binoculars during the adjustment of the interpupillary distance. If, instead, the external prisms were kept fixed, in the same way we have done with the stereoscopic microscope we have already described, varying the interpupillary distance with the binoculars, the optical paths would go outside of the hole of the light from the zoom. Another difference in comparison to the preceding project concerns the focusing device. This change would not be necessary, but it seemed useful to us to illustrate another focusing device, a system more fluid in its motion, simple to build, but also interesting from a mechanical point of view. Finally, we have added a pedestal for illumination by transmitted light. Its fabrication is optional; however, it is a very useful feature, as well as being easy to build.


CONSTRUCTION

Type of screws used- all dimensions are expressed in mm
- the dimension indicated are referred to our example
- means diameter
- M if for screws which follow the metric system of measurement
1 = pan head screw (or fillet head screw for a thicker head)
2 = flat head screw
3 = hex head screw
4 = socket head cap screw
5 = flat head socket cap screw
6 = socket set screw

As usual, we do not supply detailed drawings of all pieces, but only the general directions and many diagrams concerning the solutions we have adopted. Anyway, detailed drawings would help you very little because you hardly could find exactly the same components we have used. With the general directions, instead, you will always be able to fit the project to the pieces you have found.


PARTS OF THE MICROSCOPE

Parti del microscopioThis microscope can be divided into two parts: the optical part and the mechanical structure.

The main components of the optical part are:
- a camera zoom lens
- a box containing four prisms
- a 8x30 binocular set.

The structure is divided into:
- a pedestal with a supporting column
- a focusing device
- a linkage tube.

Later on we will see how much magnification it will be possible to attain on the basis of the characteristics of the zoom and of the binoculars. The two external prisms can be obtained from an old set of binoculars to be dismantled, otherwise they can be bought. The two internal prisms must be without bevels or rounded edges. For this reason the prisms of binoculars are not suitable, so you have to buy them. Their base dimensions and thickness should be between 12 and 20 mm.

As you see from the figures 1, 2 and 4, a binocular set is part of this microscope. It has to be a 8x30 model (where 8 is the magnification power and 30 the diameter of the objectives in millimeters). Choose a high quality instrument fitted with wide field eyepieces. This will make the observations at the microscope excellent. The binoculars will be inserted into seats on the microscope top and you will be able to remove them to observe distant objects.


PEDESTAL AND COLUMN

MATERIALS

COMPONENT

DESTINATION

Qty

18x300 chromium-plated and ground (not hardened) rod supporting column 1
30x7 aluminum rod ring for sharing the load 1
180x200, 18 mm thick black covered chipboard panel or wood board pedestal 1
h 18x760 white plastic tape edge of the pedestal 1
contact cement to attach the plastic trimming 1
8MAx40 hex head screw attaching the column 1
i 8 washer attaching the column 1
20x10 white rubber foot pedestal feet 4
3x15 self-tapping screws attaching the feet 4

As usual, when houses and microscopes are built, it is necessary to start from the foundation. The foundation of this instrument is made up of a table which also has the function of a pedestal. On it is fastened a cylindrical column. The pedestal can be made of a black painted chipboard panel. Round off the corners of the pedestal and apply a white plastic trimming around its edge. Under the table, screw four plugs of white rubber. The column has to be a chromium-plated and ground steel rod. On one end, you have to make a threaded hole to fasten it on the pedestal.


FOCUSING DEVICE

MATERIALS

COMPONENT

DESTINATION

Qty

12x50x64 aluminum plate central plate 1
12x50x74 aluminum plate upper plate 1
12x50x74 aluminum plate bottom plate 1
12x50x104 aluminum plate front plate 1
12x16x24 aluminum plate shaft support 2
10x104 chromium-plated and ground (not quenched) rod anti-rotation column 1
10x 86  chromium-plated and ground (not quenched) rod focusing shaft 1
0,7x250 steel cable for model aircraft construction (0.4 mm-diameter nylon coated steel braided cable. The outside diameter of this cable should be 0.7 mm). You can buy this cable in a model aircraft, hobby, or hardware store. cables to transmit the focusing movement 2
i 18x14 teflon coated elastic bushing upper and bottom plates 2
i 10x12 teflon coated elastic bushing supports for the shaft 2
60 knob focusing movement 2
25 knob intermediate plate blockage 1
5MAx50 threaded rod intermediate plate blockage 1
5MAx20 flat head socket cap screw fastening of the plates 4
5MAx25 hex head screw supports of the focusing shaft 2
i 5 washer supports of the focusing shaft 2
4MAx20 hex head screw tension screw for the steel cables 2
10x30, 1 mm thick stainless steel plate lock of the upper ends of the cables 1
3x4 brass bar upper ends of the cables 2
5MAx10 pan head screw mounting of the linkage tube 2

 

CarrelloINTRODUCTION
The focusing device is moved with two steel braided cables. The resulting movement is very smooth and regular. The travel range of the carriage is wide. Moreover, the carriage can be positioned at different heights along the column. This allows you to observe thick samples.

The focusing system is made up of two parts, one of which is fixed and the other movable along the column. To make it easier to understand the operation of this focusing system, Figure 5 shows in a schematic way the movable part (coloured), and the fixed part (white).

INTERMEDIATE PLATE
The fixed part of the focusing system is formed by an intermediate or central plate which is fastened to the column. For this reason, the central plate has a hole through which the column passes. This hole is made expandable with saw kerfs cut into the plate, so that it can be tightened on the column by means of a little knob. In Figure 8 you can see the cuts made on the fixed plate to make the braking device adjustable on the column.

CARRIAGE
The carriage, the mobile part of the focusing system, is "C" shaped and it is made up of three aluminum plates fastened together. Also the upper plate and the bottom one have a hole to allow the column to pass through. To make the movement of the carriage more smooth, these holes have been widened and into them have been inserted teflon coated elastic bushings which slide on the column. You need to machine the holes for the column, which are to be made on the intermediate, upper and bottom plates, with a lathe or a drill press. Other work which needs machine tools are the fabrication of the seats for the binoculars and the holes on the tension screws for the cables. All other work can be done with your own hands at the bench and with common tools such as vise, saw, file, tap threaders, square, ruler, caliper, and drill press.

Dispositivo di manovra della messa a fuoco

FOCUSING DEVICE
The shaft for the focusing mechanism and its supports are mounted on the fixed central plate. Two steel cables are wrapped for three turns around this shaft. The ends of the cables are finished with a knot. The ends of these cables are on the upper plate and on the bottom one respectively. At the bottom end of each cable there is a screw for the adjustment of the tension of the cable. Why have we used two cables instead of one? We wanted to avoid the possibility that, if the single cable broke, the carriage would be allowed to fall down on the sample. If in that moment you are observing a mineral, the risk of ruining the bottom lens of the objective would be very high. Hence, the second cable supplies a degree of safety.

Messa a fuoco

Figure 7 - Focusing device. Notice the anti-rotation column, the groove on the intermediate plate, the elastic supports of the focusing shaft, the screws which fasten the supports and which act also as a brake.

Messa a fuoco

Figure 8 - Focusing device (a knob has been removed). Notice the "C" structure of the carriage, the cables, the focusing shaft, the supports. The hole for the column on the intermediate plate is made elastic by means of the anterior cutting and other two lateral cuttings. By tightening the little knob, the plate is fixed on the column.

ANTI-ROTATION COLUMN
At this point, the carriage could still rotate like a flag around the column. To avoid this, a ground steel rod, fixed on the top and bottom plates of the carriage, passes through a groove on the fixed plate (figure 7). This groove has to be as precise as possible on the column.

SETTING THE TENSION OF THE CABLES
Each bottom end of the cables passes through a hole drilled in the screw. By turning these screws you can adjust the tension of the cables. They have to be taut enough to allow raising and lowering the carriage in a reliable way when you adjust the focusing knobs. Verify that during this operation the cables do not slide around the focusing shaft. While adjusting the tension screws you risk twisting the cables with the consequence of making them work poorly and of producing dangerous overloads. To avoid this, we have put two washers under the head of each of these screws. One of these washers is nylon, the lowest one is metal.

SETTING THE BRAKE ON THE FOCUSING SHAFT
The supports of the focusing shaft, on which the cables are wrapped, are elastic. Their stroke can be adjusted by the two screws under them. Tighten these screws as much as necessary to prevent the focusing carriage from going down by gravity. Make this setting when the microscope is complete with binoculars and objective. So, these screws and the elastic supports form the brake of the focusing device. In order to improve this device, you can insert a teflon-coated elastic bushing on each of the two supports of the focusing shaft. In this way, the shaft will rotate more regularly and the brake will be effective with less tension.

SETTING THE POSITION OF THE INTERMEDIATE PLATE
You have to do this setting when the microscope has been completed. Put a paper sheet with small print on the pedestal. By rotating the knobs, lower the focusing carriage until it approaches the supports of the focusing shaft for few millimeters. Now, move the intermediate plate up or down along the column. When you see the print become sharp, secure the plate. At this point, you will have the whole upward excursion of the carriage at your disposal. It should be about 45 mm.


LINKAGE TUBE

Tubo di collegamento

The linkage tube has the function of connecting the focusing carriage to the prism housing. It is made up of a square tube in aluminum, in which you have to make holes for the passage of the screws (see figure 9).


OPTICAL ASSEMBLY

MATERIALS

COMPONENT

DESTINATION

Qty

prism: base = 12 - 20 thickness =20 (about) central prism 2
prism: base = 20 - 34 thickness =20 (about) lateral prism 2
aluminum square tube: 50x50, L = 180, wall thickness = 2 prism housing 1
aluminum square tube: 40x40, L = 44, wall thickness = 2 central slide 1
aluminum square tube: 40x40, L = 50, wall thickness = 2 lateral slide 2
8x34x40 plastic plate support of the central prisms 1
8x34x50 plastic plate support of the lateral prisms 2
20x30, L = 176, 2 mm thick, "L" shaped aluminum bar pushing on the lateral slides 1
60x134, 0.2 mm thick, teflon or nylon sheet friction reducer for the lateral slides 2
46x46, 2 mm thick,  black plastic plate closing plug for the prism housing 2
2MAx7 flat head screw mounting the plates which support the prisms 6
2MAx4 flat head screw mounting the central slide 2
4MAx7 flat tip set screw. Its tip has to be flat or rounded to push against the "L" shaped bar 4
4MAx4 pan head screw mounting the prism assembly on the linkage tube 2
two-parts epoxy glue gluing the prisms on their support plates 1
matte (flat) black aerosol paint can to blacken the inner parts of the slides and the prism assembly 1


INTRODUCTION
The optical part is made up of the prism housing, the binoculars and the zoom objective. Figures 10, 11, 12 and 13 illustrate the prism housing and its contents. The central prisms must remain in contact with each other, so as to collect and split a light bundle of a few millimeters in diameter. The lateral prisms, instead, must follow the objectives of the binoculars during the adjustment of the interpupillary distance. For this reason, each prism is mounted inside a short square tube which slides inside the main tube of the prism housing. The external binoculars are inserted in two seats by their objectives. These seats are integral with the slides of the external prisms (figure 12). In this way, when you make the interpupillary adjustment, the lateral prisms are forced to follow the objectives of the binoculars. The common objective is mounted under the microscope by means of a suitable bayonet mount.

Scatola dei prismi

 

Components of the prism box

Figure 11 - Components of the prism housing.

INTERNAL PRISMS
The central prisms, in the same way as the lateral ones, are glued by means of a two-part epoxy resin on a plastic plate. This plate is fastened inside an aluminum square tube. In turn, this tube is fixed on the center of the prism housing.

EXTERNAL PRISMS
Each lateral prism is glued on its own plate, which is fastened inside a short square tube. These two tubes can slide inside the prism housing and for this reason we have named them slides. A "L" shaped aluminum bar, placed inside the same prism assembly, keeps the two slides aligned during their movement. The "L" shaped bar is maintained slightly pressed against the slides by means of four flat or rounded tip set screws. Two of them push from the front and the other two from the bottom. To make the movement more smooth, the two lateral slides are wrapped in a sheet of teflon or nylon 0.2 mm thick (figures 11 and 13). A series of slots allows the light to enter from the center of the prism housing and exit into the objectives of the binoculars. Two seats, one for each objective of the binoculars, are fastened on the lateral slides. In this way, when you adjust the interpupillary distance, the lateral prisms follow the movement of the objectives of the binoculars. All three tubes which are inside of the prism housing, are referred to as slides, although the central one is fixed.

Slitte portaprismi

Scatola dei prismi

 

Figure 13 - Prism Housing. Internal view (the external plug has been removed). Notice the prism, the plastic plate, the slide, the teflon sheet, the "L" shaped bar, the external tube. The teflon sheet wraps almost entirely around the slide.

Regolazione dell'allineamento dei prismiADJUSTING THE MOVEMENT OF THE SLIDES
Slightly tighten the four set screws which push the "L" shaped bar against the lateral slides. Ensure that all parts are in contact with the "L" shaped bar. Actually between them there is the sheet of teflon which wraps the lateral slides. The four set screws must not dent the "L" shaped bar, otherwise they would prevent the slide from attaining the right position. So these set screws must have a flat or a rounded tip. When you have verified that the position of the "L" shaped bar is correct, loosen the set screws a little to allow the slides to move freely, but without excess play. Use set screws with an inner hexagonal seat so the adjustment tool will allow you to move them with precision.

ASSEMBLING AND ALIGNING THE PRISMS
The prisms have to be glued on the plates in the closest position possible to the theoretical one. In spite of every care in doing this operation, the two images produced by the microscope will not be superimposed. In fact even the slightest error in the alignment of the prisms will cause this problem. To correct the alignment errors, the last prism has to be glued separately, while viewing a small test object. So the instrument has to be completed and the glue of the other prisms has to be set. The glue of the last prism has to be set well enough to hold the prism temporarily, but not enough to prevent the final adjustments of its orientation. Figure 14 shows how you have to move the last prism to correct the alignment errors of the two images. When you have finished with this operation, leave the wood wedges in place. Cut them when the glue has completely hardened.

BLACKENING OF THE INTERNAL PARTS
To avoid light reflections which would lower the contrast of the images, the internal surfaces of the prism housing and of the slides have to be blackened with a matte black aerosol paint. Do not blacken any optical surfaces. You should also avoid blackening the plastic plates of the prisms.


MOUNTING THE BINOCULARS

COMPONENT

DESTINATION

Qty

8x30 binoculars with wide field eyepieces to observe the images produced by the common objective 1
45x16.5 black PVC or other plastic material seats for the objectives of the binoculars 2
2MAx7 flat head screw mounting the seats for the binoculars 6

The objective end of the binoculars have to be inserted into the seats fastened on the lateral slides. As these slides are mobile, they will follow the objectives during the interpupillary adjustment. The length of the slides and of the external tube allow the binoculars to vary the interpupillary distance between about 45 and 75 mm.


CHOICE AND MOUNTING OF THE OBJECTIVE

MATERIALS

COMPONENT

DESTINATION

Qty

Zoom objective for reflex camera.
Suggested focal length: 35 - 200
common objective 1
10x162 steel or aluminum rod spacer for the objective holder plate 2
100, 1 mm thick stainless steel sheet plate to mount the bayonet seat 1
bayonet or threaded mount, suitable for the objective mounting the zoom objective 1
3MAx7 socket head cap screw mounting the objective holder columns 2
4MAx7 socket head cap screw mounting the bayonet joint holder plate 2
i 4 washer mounting the bayonet joint holder plate 2
2MAx5 flat head screw mounting the bayonet joint 3

 

CALCULATION OF THE MAGNIFICATION POWER OF THE MICROSCOPE
The power of this microscope is given by:  Im = 250 x In/Fo
where:
Im = power of the microscope
In = nominal power of the binoculars
Fo = focal length of the common objective
Let us distinguish a minimum power (Imin) and a maximum power (Imax)

For example, using a 35-200 mm zoom objective and a 8x30 binoculars set, you will obtain a continuous variation of the power between 10 and 57 X:

Imin = (250 x 8)/200
Imin = 10 X

Imax = (250 x 8)/35
Imax = 57 X

CHOICE OF THE OBJECTIVE
There are two main kinds of objective for a reflex camera: the normal one and the compact one which has aspherical lenses. Both types work fine, but with the compact objective you will make a less bulky microscope. As you have seen, the power of the microscope depends on the focal length of the common objective and the shorter it is, the higher will be the power of the microscope. As we use a zoom objective, its longest and shortest focal length will correspond the lowest and the highest power. It doesn't suit you to go under 10 magnifications for minimum power and for maximum power it doesn't suit you to go much beyond 50 magnifications because the image tends to lose its sharpness. With a 35-200 mm focal length objective you will obtain a range of magnifications between 10 and 57 X. For our microscope we have used a 28-200 objective which we already had at our disposal and we have obtained a range of magnifications between 10 and 71 X. This objective offers a wider range of magnifications, but over 50 X, a diffused and very bright illumination becomes necessary. Instead of the zoom objective, you can use fixed focal length objectives. In this way, however, you will again have a step by step variation of magnification power. In other words, to change the power you will have to replace the objective with another.

MOUNTING THE OBJECTIVE
You have to mount the objective so that the part which usually sees the film is facing the sample you observe. This serves to allow the objective to work in the correct way from an optical point of view and as a result, to obtain sharper images. Mount the objective on a plate on which you have fastened a proper bayonet fitting. The plate is kept at the necessary distance by two metal rods.


FINISHING

APPLICATION OF THE PLUGS
It is necessary to apply plugs to the extremities of the prism housing. These plugs serve to prevent light entering, and lowering the contrast of the image. The plugs also will reduce the quantity of dust which will be deposited on the prisms. The plugs can be obtained from a black plastic sheet 2 mm thick. They will have a square shape and will simply be inserted by a press fit inside the square tube. You also have to apply a plug on the linkage tube. It has only an aesthetic function.

Tavolino per illuminazione in trasparenza.TRANSPARENT PEDESTAL
Often, the translucent samples are better seen when illuminated by transmitted light. They will show details of internal structures which could not be perceived by reflected light. This is, for example, the case of larvae of insects which you can find under the stones in river beds. It is not difficult to build a pedestal for transmitted illumination. As you see in figure 15, it is sufficient to place under the pedestal an adjustable mirror. In this way, by shining some light on the mirror, you will be able to direct it in a suitable manner onto the bottom of the sample. It is better that the mirror is reflective on one side and white opaque on the other, so it is also possible to produce a diffused light. This system of illumination requires raising the pedestal about 50 mm. You can adopt this solution also for the normal stereoscopic microscope which we have described in a preceding article.

BOX AND BELL
Store the microscope in a wooden box when you are not using it. Build the box in a way it can also hold the binoculars, a 20-Watt halogen lamp, and the accessories. The box should be dust-proof, hence the window should close on velvet borders. Instead, if you prefer to leave the microscope in view on a piece of furniture, it will be necessary to protect it from the dust. To this purpose, you can use a transparent plastic cover. The best solution is to make a bell in transparent plexiglas. You can cut the plates and stick them with silicone, in the same way you build an aquarium. If you want to make a more attractive case, you can hot-bend a sufficiently long plate and close the sides with two other plates, using a solvent glue designed for plexiglas.


USE OF THE MICROSCOPE

ADJUSTMENTS
If necessary adjust:
- the set screws of the prisms housing
- the tension of the cables of the focusing system
- the brake on the carriage
- the position of the intermediate plate along the column
- the interpupillary distance of the binoculars
- focus the binoculars to the infinity
- insert the binoculars in their seats and place them in center
- open the diaphragm of the zoom at the maximum

When you adjust the interpupillary distance, the images can split. Shift the position of the binoculars a little until they overlap again. (In fact, moving the binoculars causes a slight change in the position of the slides, hence the prisms.)

Adjustment of the parfocality.
The parfocality is a condition in which, when you vary the magnification, the image remains in focus. If this does not happen, try to modify the focusing of the binoculars or of the zoom objective until you achieve it.

SUPPORTING PLANE
As this microscope is rather tall, if you want to use it when you are sitting, you have to put it on a low surface.

ILLUMINATION
With a quite powerful and directional light, you will have good light and shadow effects which will bring out the relief and the colors of the samples. To this end, you can use a 20_Watt halogen task lamp. There is a model with a magnetic support which allows you to orient the lamp. Unfortunately, this light gives off a lot of infrared radiation. If you want avoid desiccating the insects you are observing, avoid prolonged exposures to strong light and release the specimen soon after the observation. To reduce this problem, filter the light using a heat absorber filter that gives a more cold light. You can find such filters in slide projectors or in a camera shop. Usually illumination by transmitted light requires a less powerful lamp, but one adjustable in intensity. Try bare filament and polished-reflector lamps.

Over 50 magnifications, you will have to supply a bright and diffuse illumination, otherwise the resolution of the microscope will be lowered. Outdoors you can use the direct light of the Sun. Anyway, as it come from a perceived point source, this light is not suitable for high magnifications because it produces a sort of grainy appearance, which decreases the sharpness of the images. In this case, to perceive the tiniest details, place a white screen around the sample to obtain a diffuse illumination.

The quality of the image depends mainly on the quality of the optics you use for the construction of this instrument; however, you will soon notice that the illumination also has a great effect.

ACCESSORIES
The stereoscopic microscope is a research instrument. During the observations, you may wish to manipulate the samples, hence you will need some tools such as the following:

- petri dishes to hold fluids or insects to be examined
- a pair of tweezers with thin tip
- a black and a white card on which to place the object and easily move it
- plastic jars or vials with screw caps to collect samples of water from ponds
- a glass Pasteur pipette with rubber bulb
- some transparent boxes to collect insects
- a box to collect vegetation, lichens and mushrooms without crushing them
- a bag to collect humus
- a heat absorber filter for the spot light
- screwdriver and spanners (wrenches) to adjust the microscope


MAINTENANCE

Keep this instrument in a dry room and if it is possible in its box. Do not leave it exposed to dust, but cover it. Now and then, check that the column is clean. If necessary, clean it with a dry cotton cloth. Verify the instrument works fine and adjust the screws if necessary. Try to avoid the need to clean lenses and prisms. Optical surfaces should rarely be cleaned and this operation has to be performed with great care. To this end, use special optical paper, or a clean cotton cloth. Do not use ordinary paper because often it contains minerals used as fillers (i.e: kaolin) which would ruin the lenses.


OBSERVATIONS

With this microscope you can do an innumerable quantity of observations. In fact, this type of instrument is particularly suited for the investigation of the natural world. In the article on the other stereoscopic microscope we have already supplied some suggestions of possible observations which are valid also for this model. So, we limit ourselves to add some other suggestions.

The observation of an anthill is surely fascinating. You will see many ants come out of the tunnels bringing a sand grain in their jaws. Ninety percent of the time, they lay it in a too high place, so the grain will roll again into the tunnel. Other ants carry a grain at the highest place possible, like the top of grass blades, and they let it fall... again into the nest. This will not prevent the ants from carrying the ground out of their nest, creating what is a mountain for them. A similar thing is the transport of food in the nest. Often many ants are engaged in the transport of the same object. Each of them pulls to its side. The object moves randomly. No one knows how, but in the end they succeed in reaching the entrance of a gallery and disappearing inside it. Raising a stone, often you will discover the nursery of the anthill. Be quick to place the microscope because in a short time the ants will remove the larvae into the shelter of their nest. What about the war among ants? This event is not preceded by war declarations, so it is not easy to observe. Anyway, if it happens that you notice an unusual dark stain in your garden, approach it: it is possible that it is a battle between opposed ant armies. Watching this fight with the stereoscopic microscope is an impressive thing: soldier ants equipped with powerful jaws pierce through the belly, the thorax or the head of each other. After a while, the struggle ends. Worker ants will arrive to evacuate the dead bodies which are carried in a special dumping-cemetery and the mysterious stain will disappear in silence, as it appeared.

To comfortably observe an ant hill, you may obtain a steel tube with the same diameter of the column of the microscope and mount the instrument on it. At this point, you can drive the tube into the ground near the ant hill. To avoid taking the microscope off its column, you can prepare a fitting which allows you to connect the column to the tube to be driven into the ground.

The dytiscus is an aquatic coleopter large as a phalanx of a finger. Also its lava lives in water. It is a ferocious predator. It has huge sharp jaws, like sickles. With them, it injects into the victim a proteolytic fluid, then it sucks its substances. At the end, what remains of the victim is the external skin only. Observing the larva of a dytiscus when it captures a boatfly, kills it and devours it is a impressive sight.

Also the larvae of dragonfly can offer a similar bloody spectacle, anyway, when they are young, they limit themselves to capturing water fleas. To do this, they evert a pair of jaws "mounted" on an articulated arm placed under their throat. This movement is so quick that the human eye is not able to follow it, but you can see the animal while it is chewing the unhappy shellfish. Particularly elegant are the larvae of damselflies.

Butterflies are very beautiful, and observing them through the microscope is surely spectacular. Their coiled proboscis, the instrument with which they suck the nectar of the flowers, is indeed interesting. Also their compound eyes are fine to see, but the colored scales which cover the wings and the body of these insects is what is most fascinating about them. These scales have a different color and shape according the position on the wing and on the body. To observe a butterfly, you can place the microscope in the garden or in a field, close to flowers which are visited by these insects. To this end, you can use the same technique we have suggested to observe the ant hill. You can also capture a butterfly and place it in a transparent box. To keep it motionless, offer it some drops of honey mixed with water.


CONCLUSION

Who ever would have said it was not possible for someone to build a zoom stereoscopic microscope by himself? And yet here is the complete design. What is more, it is not even difficult to make this instrument. Obviously it is necessary to commit yourself a little. We live in a time in which we are accustomed to push a button to obtain immediately what we want. We let ourselves go more and more to watch spectacles, but during these shows we stay passive, we do not make any effort to create anything. After some years passed in front the television, many people start to show signs of suffering. It is a subtle and persistent pain, of which most people do not understand the origin. Building something with your own hands means recovering the use of your manual ability, your creativity, your ability to reason and the use of your mind. These are components of our soul which need to live, to be expressed. In this way we regain our equilibrium and with it our serenity. Often we start jobs which we leave half done. These things held over do not leave us in peace. If this often happens to you, try at any rate to complete this instrument. Sure, it is a good challenge, but to win it by completing the microscope will gain you a precious self-confidence. Making something with our own hands is much more satisfying than to receive the same object as gift, it means also to immerse yourself into an endeavor in a much deeper way and conquer a piece of reality. In order to build this microscope, you will have to redo the project, to obtain the components, to work them, to mount them, to adjust them. You will have to do all the adjustments. But when you have completed the instrument, you also will want to use it and you will want this much more than if you had received it as gift. Then, almost by magic, this instrument will become a guide which will encourage you to discover nature. To fabricate this instrument is not only a financial advantage by the money you save instead of buying it, it also lifts you out of the banality of the civilization of disposable things, to face something in a systematic way, with dedication. At the end, you not only will have the microscope, you not only will have acquired or enhanced your fabrication capabilities, but also you will have conquered wide spaces in the fields of optics, mechanics, and nature - spaces in which you will move at ease. You also will have gained for yourself an interest in these fields. These interests, this experience in meeting the challenge of mastering the demands of such a project, and the confidence in your capabilities are even more important than the same instruments you will have built.


SOURCES OF PARTS

Here are a few sources for the US builder to obtain parts:

Edmund Scientific: www.edsci.com
Surplus Shed: www.surplusshed.com
Sterling Resale Optics: www.sro-optics.com

Metal and plastic parts:
Small Parts, Inc.: www.smallparts.com
McMaster-Carr: www.mcmaster.com

Another source is to get friendly with some local machine shops, as they usually have lots of small pieces of raw stock left over from various projects. They usually don't sell to the public, so get to know them first.


BIBLIOGRAPHY

Here, we give to you some useful links to increase your knowledge of the stereoscopic microscopes and of microscopy in general.

Introduction to Stereomicroscopy  A very good description of the stereoscopic microscope. Produced by Nikon in collaboration with Molecular Expression.
MicroscopyU  Articles and links of high interest on the microscopy. Produced by Nikon in collaboration with Molecular Expression.
Molecular Expression   Introduction to Optical Microscopy and Photomicrography. This website also supplies a lot of very interesting articles and links on microscopy.


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