A Simple DIY
Stereoscopic Microscope

G. Carboni, January 2006
Translation edited by Drosera

TABLE OF CONTENTS INTRODUCTION THE STEREOSCOPIC MICROSCOPE FEATURES OF THIS MODEL COMPONENTS AND MATERIALS CONSTRUCTION TOOLS BUILDING PROCESS MAIN DIMENSIONS OF THE MICROSCOPE BASE SUPPORT COLUMN FOCUSING SYSTEM -  GUIDES -  CARRIAGE -  MANEUVERING DEVICE --  Mounting the cable --  Adjusting the brakes of the carriage FASTENING THE ACHROMATIC LENS MOUNTING THE COMPACT BINOCULARS FINISHING MAGNIFICATION OF THE MICROSCOPE USING THE MICROSCOPE CONCLUSION

INTRODUCTION

Another stereoscopic microscope? Actually, I was not thinking about writing another article on this topic, but a good idea convinced me to do it. In fact, I didn't think it was possible to further simplify the project of the dissecting microscope already published in this gallery. I also thought my readers had enough examples for building microscopes, but a friend gave me a ground-breaking idea, and I just had to include it. This innovation to the original project makes the prism box useless. This box was quite difficult to build, and its elimination simplifies the project and make the fabrication of the microscope easier.

How did I get this idea? I was at the First Tuscan Meeting of Amateur Microscopy which happened May 30th, 2004, in the small town of Pieve a Nievole, near Florence. I had just finished arranging my hand-made microscopes on my display table, when a microscopist friend approached me. He held a compact porro prism binocular, a binocular in which the objectives are very close, nearly in contact with each other, and he used them to see through a 50 mm lens which was sticking out of a microscope of mine. He said , "Good heavens, how well I see through here!". When I saw this, I understood the importance and the usefulness of combining that kind of binocular with an achromatic lens of the appropriate diameter.

In the first model of stereoscopic microscope, it was necessary to make a box for the prisms in order to bring in the light at the end of the objectives of a normal pair of binoculars. In this case, the objective of the compact binoculars were able to keep themselves inside the diameter of the lens, and the box of prisms was completely unnecessary. "Damn!", I said to myself that day, "How come I didn't think of this before?".

THE STEREOSCOPIC MICROSCOPE

What is a stereoscopic microscope? It is a microscope in which the sample is observed from two slightly different angles, to obtain two slightly different images, which when combined produce a three-dimensional view. This instrument works with low magnification, and is particularly suited to observing flowers, insects, minerals, and other samples whose sizes are somewhere between a tenth of millimeter and few centimeters.

FEATURES OF THIS MODEL

Figure 2 - By placing a pair of compact binoculars on an achromatic lens which is wide enough, it is possible to see objects sharply magnified, lying at the focal distan- ce from the lens. What is lacking is the body of the mi- croscope. In this article, I will deal with its fabrication.

Figure 3 illustrates the optical scheme of the microscope we are preparing to build. The philosophy which inspires this project is that of simplicity. To build the pedestal, we will use wooden boards. For the focusing system, we will use a carriage moved by a steel cable. With these solutions, this model of microscope is particularly simple to make. If you use good quality optics, you will obtain wide, sharp, and clear images. This microscope will provide only one magnification, around 12 X, and its' ease of use makes it suitable for children.

COMPONENTS AND MATERIALS

COMPACT PORRO PRISM BINOCULARS
In order to build this stereomicroscope, you have to obtain a pair of compact binoculars. These binoculars are made with two objectives of a small diameter and which are close enough together to make it pocket sized (figures 4 right and 5 right). On the market, you can find compact binoculars starting from 12 euro. The one I bought is made in China, and costed 16 euro, and works well. Quality compact binoculars can cost more than 50 euro, but you will have the advantage of increased sharpness of the images, a wider field of observation, and easier use.

When buying your binoculars, check that the images they form are sharp and the field of view is wide. In a stereomicroscope, a wide field of view makes observations very striking. Check that the eyepieces are comfortable and not difficult as can happen with certain optical devices. For example, if the exit pupil of the binoculars is too close to its eyepieces, it can be an effort to keep your eyes open. It is important that two objectives should be within a diameter of 50 mm, or at the very least not more than 60 mm. Finally, check that the binoculars can stand on their wide ends without falling, so that they can be supported when you place them on a plane by their objectives.

ACHROMATIC LENS
You must obtain an achromatic lens of 50 mm in diameter and with a focal length of about 200 mm. For this purpose, an objective lens of normal binoculars is suitable (figures 4 and 5 to the left). It is possible to obtain lenses of this kind from old/used binoculars, or from cheap binoculars you buy for this purpose in shops or from street vendors. Usually, the binoculars made in Russia are cheap and have high quality. Before you buy a pair of binoculars, check that you can see well through it, and that it is exempt from chromatic aberration and other defects. The objectives of the compact binoculars have to be comprised for the main part inside the diameter of this lens (figure 3). From now on, we will call this common objective an achromatic lens. This will help us to avoid confusion between the compact and dismantled binoculars

In figure 2, you can see that it is sufficient to mount the compact binoculars on the achromatic lens to obtain a stereoscopic microscope. What it lacks is the body of the microscope, a device able to keep the optical components in place and which allows you to focus the sample. Looking through the microscope without a support can cause dizziness. This article deals only with the manufacture of the pedestal and of the focusing device of this instrument.

MATERIALS

You can buy the chrome plated and ground steel bars in a hardware store, an industrial component store or a ball bearing store.

CONSTRUCTION

TOOLS
To build this instrument, you don't need any heavy-duty machinery. You will need a table fitted with a vice and some common household tools for D.I.Y., such as: hacksaw for cutting metal, files, calipers, set-square, a marker that can draw on metals, bits for threading, etc. You will however need a drill press fitted with a vice to grip the pieces to be drilled. If you have access to a lathe, the work will be easier. It will also help you in making the borders of the metal plates, otherwise you will have to work them with a file and this will take a much longer time.

BUILDING PROCESS
Before you start working, here is some advice to follow for metalworking. Often, you need to fasten 2 pieces by means of screws. If you drill the pieces independently from each other, usually you will unable to mount the second screw because the holes on the pieces have a difference in the clearance in relation to each other. Not only this, but when you mount them you can also have alignment errors of the pieces. To avoid these problems, the second piece has to be drilled while using the first one as a drilling guide. Moreover, it is necessary for the two pieces to be well aligned to each other. In practice, you have to make the first hole in the two pieces, then mount the first screw, align the pieces and block them in the vise of the drill press or with another system, finally make the second hole in the two pieces at the same time. When it is possible, you can also follow the simpler way to drill the two pieces superimposed and blocked on the vise of the drill press.

DETERMINING OF THE MAIN DIMENSIONS OF THE MICROSCOPE How high should the column be? At what height do I have to mount the achromatic lens? In this paragraph, I will try to answer to these and similar questions. Mount the compact binoculars on the achromatic lens, and by makeshift means, clasp them at a height which allows you to clearly see the minute writing placed on the table. Now, measure the distance "X" as shown in figure 6. Height of the column: In order to make room for the observer's nose, the column has to be at least 40 mm lower than X. Height of the guides: The upper support of the guides has to be at the same level as the column. Height of the achromatic lens: When you have finished the pedestal and the focusing device, you can mount the achromatic lens on the carriage. The height of the achromatic lens must be equal to X - h, where 'h' is the height of the compact binoculars. While you are doing this operation, keep the carriage raised 4 mm from its lower stop (figure 6). In this way, you will have a margin for allowing people with a different eyesight to yours to focus a thin sample placed on the table of the instrument. From this position, the carriage can be shifted about 80 mm upward, which will be more than enough to focus most of the samples you want to observe. The sizes shown in the following diagrams are those of my own microscope.

BASE
You can make the base with a wooden board (figure 7). Or a chipboard coated on both sides with black formica is good. Round the four corners and line the borders with a plastic ribbon (glue with mastic, then trim with a sharp knife). There is also a ribbon which can be set using a hot iron. Under the base and near the four corners, fasten as many plugs of white rubber or felts as you feel necessary.

SUPPORT COLUMN
The support column is used to support the instrument. It is made of a little wooden board supported by another little board which improves its' stability. The two boards are fastened together, and then onto the base. With a file, correct the lower surface of the column so that it is orthogonal in relation to the base. If the column and the microscope are not well aligned in relation to the base, slightly widen 2 of the 3 screw holes which fasten them to the pedestal, then correct the alignment and lock them.

FOCUSING SYSTEM

COMMERCIAL SOLUTION - The simplest solution is to buy a pre-made focusing device. There are many ways to obtain this, but they are not always suitable. Use a focusing sled for cameras. Sleds of this type are made by ROWI, HAMA, etc. In ball bushing stores, you can find devices named "linear ball bushings", "linear sliding systems", etc. Also Edmund sells focusing devices suitable to our case, but they are quite expensive. Most devices of this type are lacking in the maneuvering system. If you wish nonetheless to obtain one, you can refer to the solution I will describe further on. If you do not succeed in finding a suitable commercial device, the solution I suggest is simple enough and will work very well.

HAND MADE SOLUTION - This solution consists in making a carriage which slides on cylindrical guides. The movement of the carriage is provided by a steel cable. It is a simple solution which does not require the use of special machine tools.

Let us distinguish between three different parts in this system: 1 - guides; 2 - carriage; 3 - maneuvering device. The carriage slides along the guides and it is moved by the maneuvering system.

GUIDES
The guides are made of two cylindrical bars, 8 mm in diameter, in chrome plated and ground steel (not quenched). These guides are mounted on an aluminum plate, 2 mm thick, by means of two aluminum supports (figures 8 and 9).
To reduce the errors of parallelism to a minimum, keep the two supports superimposed and tight in the vice of the press drill while making the holes for the guides. Fasten the supports to the plate by means of 2+2 screws (figure 9). Fasten the plate to the support column by means of 6 screws.

Very likely, when you mount the guides in their supports, you will have alignment errors. Figure 10 indicates how to correct these errors.

On these supports, make the holes for the cable. On the upper support, also make a threaded hole for the screw which will stop the cable (figures 9 and 16). You can also make these holes when you have finished the carriage and mounted the maneuvering bar, so that you will be able to determine their exact positions.

CARRIAGE
The carriage is made up by three aluminum plates assembled with screws. The upper and lower plates have 2 holes each to allow the guides to pass. They also have a hole for the steel cable. In this case too, you can make these holes when you have already mounted the maneuvering bar. In the images below, you can also see the lateral supports for the maneuvering shaft and the knobs.

If the holes for the guides made on the supports (figure 9) have a difference in the clearance in relation to the corresponding holes on the carriage, it will not slide. To avoid this difference, make the holes on the carriage by using a support of the guides as indicated in the paragraph, "Building Process". In order to make the movement of the carriage smoother, use opened bushings (in this case, the holes on the carriage have to be widened. The outer diameter of the bushing I used was 10 mm). Usually, it is necessary to widen the cutting of the bushings by means of a saw. Correct the alignment of the holes likewise indicated in figure 10. This adjustment should allow the carriage to smoothly slide on the guides.

Now, mount the carriage on the guides and the guides on their supports. At this point, the carriage has to slide easily and smoothly. If this does not happen and the carriage moves only for a short distance and then becomes increasingly resistant, this means the guides are not parallel. No worry, the problem can be solved. To this end, it is necessary to use the left guide for the function of main guide, while the right guide will only have the function of preventing the carriage from rotating around the axis of the first guide, like a flag.

In practice, it is necessary to permanently remove the upper right bushing (figure 12) and with a round file make the hole oval for the lower right bushing as is shown in the figure 13. Notice that the axis of the oval is in the direction of the other hole. As the upper right bushing has been removed and the lower right bushing is now free to move, the carriage will always be able to slide normally even if the guides are not parallel. At the end of this work, the oval hole should have a diameter of about 10.5 mm on the wider end, and of 10 mm on the other. In summary: the carriage will be provided with two bushings on the left guide and only one on the right guide, mounted in the oval hole. If it has a tendency to slip off, open the bushing a little.

On the front plate, make a hole of a dozen millimeters in diameter which will help you to see and to arrange the coils of the cable.

MANEUVERING DEVICE
The maneuvering device has the function of bringing the carriage, and with it the optics of the microscope, to the right height to focus the sample and keep it in this position. This device uses a thin steel cable made of a flexible braid which is wrapped around a ground bar on which you will affix the knobs. You have to work the extremities of this bar to fix the knobs.

The maneuvering shaft is affixed to the carriage through two lateral supports which also have the function of braking mechanisms (figures 11, 12 and 16). To this end, the hole of these lateral supports is made elastic by means of a cutting of saw and can be tightened with a screw. After you assembled these supports and before mounting the shaft, you have to pass a drill through both the holes to remove any alignment errors. Also the cutting of these bushings have to be widened. In this case, make the alignment correction of the holes as indicated in figure 10. In the end, the shaft has to rotate freely in its bushings.

If you haven't already done it, make the holes for the passage of the steel cable corresponding to the positions A, B, D, E of figure 16. The positions A and E have to be done so that the cable is tangent to the maneuvering bar. The holes in A and E have a diameter of 1 mm, those in B and D have a diameter of 5 mm. MOUNTING OF THE CABLE The cable is made of a thin iron braid covered with nylon. Cut a piece 320 mm long. As shown in figure 16, the cable is fixed to the supports of the guides. To make its mounting easier, remove a support of the shaft (figure 14). Make a knot on an end of the cable. As shown in figure 16, pass the free end of the cable through the hole A (the cable will stop at the knot). Pass the cable through the hole B. Wrap 3 coils around the shaft C. Pass the cable through the hole D. At this point, the coils of the cable tend to overlap each other. By helping yourself with tweezers and screwdriver, arrange the coils. As soon you manage it, keep the cable a little taut to avoid the coils overlapping and pass it through the hole E, then tighten the stop screw. Mount the support of the shaft you removed earlier, relax the screw which stops the cable and, with pincers, pull it with a force of a pair of kg, then tighten the stop screw again. Move the carriage and arrange the coils. If necessary, repeat the draught of the cable. If the cable is pulled properly, by rotating the knobs, the carriage must to lift in a gentle way and without slipping. Cut the excess cable, but leave a couple of centimeters in case any further corrections of the tension are necessary. To avoid that the upper extremity of the cable ends up in the nose of those who use the microscope, you have to bend it and to fit it in a little hole made near to that from which it comes.

ADJUSTING THE CARRIAGE BRAKES
After you have mounted and pulled the cable, if you free the knobs the carriage should go down quickly because of its own weight. To help it keep its position, tighten the brake screws of the supports of the maneuvering shaft as necessary.

An alternative solution for the maneuvering device is to use a couple of rack-and-pinions instead of the cable-shaft. You can do it, but I recommend the system with the cable because it is simpler to do, it is cheaper, it works better and has a smoother ride.

MOUNTING THE COMPACT BINOCULARS
Now, what it is left to be done is to secure the compact binoculars onto the achromatic lens. The binoculars should be placed on a plane. If you have a lid for the achromatic lens, make two holes in it to allow the light to enter the compact binoculars, mount it on the achromatic lens and place the binoculars on it. The lid is not indispensable, but it is better to avoid having the compact binoculars directly put on the achromatic lens. So, you ought prepare a support plane to be placed on the achromatic lens. Unfortunately, this position is not stable and probably will cause the binoculars fall. To avoid this, you have to make a stirrup with which to secure the binoculars. The correct solution will depend on the binoculars you bought. In figure 19, you can see the stirrup I made for my microscope.

FINISHING
To complete the instrument, you can make a base for the observations in transmitted light as shown in the article on the stereo-zoom microscope: http://www.funsci.com/fun3_en/uzoom/uzoom.htm. You can also make a wooden box to house your microscope and its accessories. You can finally place a plate with the date of construction and your name on the instrument.

MAGNIFICATION OF THE MICROSCOPE

The power of this microscope is given by: Im = 250 x In/Fd

where:
250 is the conventional reading distance (in mm)
Im = power of the microscope
In = nominal power of the compact binoculars
Fd = focal length of the achromatic lens (in mm)
By using compact binoculars with 8 X, if Fd is 190 mm, you will have:

Im = (250 x 8)/190

Im = 10,5 X

If instead you use 10 X compact binoculars, the power of the microscope will be 13 X.

How you can determine the Focal Length (F) of a lens? Place the lens between a lamp and a screen. Focus the lamp on the screen. Measure the distance from the lens center to the lamp (distance A), and the distance from the lens center to the screen (distance B). Then the focal length is given by:

F = AxB/(A+B)

USING THE MICROSCOPE

Before starting with any observations, adjust the interpupillary distance of the binoculars to your eyes, then set the focus to about infinity, or on a distant object. Now you can place the binoculars on the achromatic lens of the microscope and begin your observations. To focus the samples, do not directly use the focus system of the binoculars, but always use the knobs of the microscope. If another person want to use the microscope, make him to re-adjust the interpupillary distance for his eyes, and make sure that he does not move the focusing system of the binoculars, which must always remain set to infinity.

Obtain a black, a white and a gray card. Place the samples on the card which allows you to see best. Usually black card is more suited for white samples and vice versa. It is also useful to move the samples during the observations. The microscope performs well also in natural light, but in the evening, you can use a lamp or other light source.

Directional lighting like sunlight or a spotlight enhances the plasticity of the sample, by providing a beautiful show of lights and shadows, but it has the disadvantage of lowering the sharpness of the image. In fact, using a luminous source of small size is like tightening the diaphragm of a camera or of a normal microscope: the contrast increases, but the sharpness decreases. So, if you prefer to see the colors and shapes, use a directional lighting source. If you prefer to observe the finer details, use a diffused lighting source. By using a translucent paper or plastic sheet, you can also turn sunlight into diffused lighting. Another strip of paper placed behind the sample also increases the diffusion of the light. Another way to obtain diffused lighting is to use a little toroidal neon lamp placed under the achromatic lens. You can also try to obtain intermediate lighting conditions, by sending directional lighting, and by reflecting or diffusing some of it.

Make sure nobody touches the lenses, otherwise the fingerprints will blur the images. Clean the lenses as little as possible. Do not worry if there are particles of dust on them. If you want remove them, use a soft and clean brush. If you want to clean the lenses, first remove the dust with a brush, then clean them with a piece of moist cotton fabric or with a suede skin. Never use common paper, but only special optic papers. In fact, in common paper there are mineral powders which would scratch the optical surfaces, ruining them. On the contrary, the paper for optics is made up of pure cellulose. To remove fingerprints, use a fabric moistened in alcohol, then a cotton fabric slightly moistened with water so to remove any remaining halos.

In the box of the microscope, keep also the compact binoculars, a light source, and accessories like a pair of tweezers, a knife, petri dishes, little boxes and pots with lids to keep samples, a dropper, the black, white and grey cards, etc. Also keep the tools for adjusting the microscopes, like screwdrivers and wrenches. Finally, keep a supply of steel cable.

Whenever you are finished using the microscope, place the compact binoculars in its case. To avoid dust settling on the achromatic lens, cover it with a plastic bag and place the microscope in its box.

CONCLUSION

Et voila! An easy to build model of microscope! As stated earlier, people who do not want to work too much or who believe they are unable to build it, can use a pre-made focusing system. On the other hand, if you do want to build it, it is not difficult to make. Even with a little cost, the optical quality of this microscope is high and definitely better than many commercial models available to the general public. People, what are you waiting for? Wouldn't it be great to give your children or grand-children an instrument made by your own hands, that will forever remain a treasured souvenir from you? I'd love to see some pictures of you near the little machine you just built! I also welcome any comments about the construction or usage of this instrument.

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