A Simple
Stereoscopic Microscope
Giorgio Carboni, October 2004, redesigned in
March 2008
Translated by Sarah Pogue in Mai 2010
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Figure 1 – The completed stereoscopic microscope. |
Another stereoscopic microscope? In fact, I had no intention of writing another article of this type, but then a good idea pratically obliged me to do so. In reality, I didn’t think it was possible to further simplify the stereoscopic microscope project already published in this gallery. I also thought that you would have had enough of constructing microscopes, but I couldn’t resist letting you know a new idea that makes the project even simpler.
On sale, there are binoculars whose objectives are very close to one another, almost touching. Their characteristic is that of being small in size and able to fit into your pocket (figures 7 and 8 on the right). These are called compact binoculars. The idea that characterises this stereoscopic microscope model is that of using compact binoculars to look through a sufficiently large lens (figures 2, 4 and 6). With this system, you can build a stereoscopic microscope without having to construct a prism box. This simplifies the project and makes the construction of this microscope easier. This project is also characterised by a microscope body equipped with a focusing system that is easy to realise, also suitable for those that know how to work wood.
I will briefly remind readers who do not know what a stereoscopic microscope is. This is a microscope with which the sample is observed from two slightly different directions in order to obtain the images necessary for three-dimensional viewing. Typically, these instruments work at low magnifications and are particularly suitable for observing flowers, insects, minerals and other samples that are between a tenth of a millimetre and a couple of centimetres in size.
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Figure 3 – Step 1: unscrew one
of the objectives |
Figure 4 - Step 2: place a
compact binoculars |
Figure 5 - Step 3: a model of the device
that |
STEP ONE
Take a pair of binoculars, remove one objective and place it in front of the
other as shown in figure 3. Looking through the binoculars, move towards or away
from an object until you see it clearly. This is already a microscope. It is
missing the stereoscopic vision because you can only look with one eye.
STEP TWO
Now mount a pair of compact binoculars on a binocular objective with a diameter
of 50 mm, as shown in figure 4 (pay attention to the orientation of the common
objective). Again, in this case, move towards or away from an object until you
see it clearly. This time, apart from seeing the object enlarged and clear, you
will also see it in relief. This happens because each eye sees the sample from a
different direction (figure 6). In this way you will have a stereoscopic
microscope.
STEP THREE
Both of the improvised microscopes that we have constructed have the defect of
lacking a support structure, and with your hands you will not be able to keep
them still. For this reason such microscopes would be pratically impossible to
use. With a simple support and a device such as that indicated in figure 5 we
can give stability to the instrument and realise the focusing system. As you can
see, at the extremity of a piece of wood two supports are fixed. These supports
sustain a guide along which a wooden carriage slides. To move the carriage
backwards and forwards, it is necessary to mount a transverse bar around which a
cable is wound that will be fixed to the two supports. In this model, I used a
piece of electrical cable because it is highly visible, but in the microscope
that we will construct we will use a thin steel cable that can be bought in
model airplane shops.
At this point, all that is left to do is mount the objective. For this purpose, we will use a V-shaped support.
If you want to construct this microscope, do the simple tests that I have just described. Build also the model for the focusing system. It is not indispensable, but you will need it to better understand the structure of your microscope. Finally, carefully observe all of the images in this article.
OPTICAL SCHEME OF THIS MICROSCOPE
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As illustrated in figure 6, a pair of compact binoculars is positioned above a lens sufficiently large to contain the objectives of the binoculars. If we place this lens at the focal distance from the sample to be observed, the light rays that come from the sample and which pass through the lens will become parallel. But the binoculars that are above the lens are made to observe distant objects, and therefore parallel light. Consequently, the image of the sample will be formed in front of the eyepieces which will in turn contribute to magnifying the image. Many stereoscopic microscopes are made from two paired microscopes that converge on the sample. With this microscope model, called “common objective”, it is not necessary to use two microscopes, nor is there the mechanical problem of keeping them aligned or of consenting variation of the interpupillary distance without losing alignment. In fact, the common objective allows the two optical paths to converge exactly on the sample. Regulating the distance of the binocular eyepieces, the optical paths move further away from and closer to each other, but they always converge on the focus of the common objective. This occurs on the basis of the properties of the converging lenses according to which the light rays parallel to the optical axis that pass through the lens pass through the focus of the same. Inversely, light rays that depart from the focus of a lens and that pass through it, exit parallel. How can we know if the common objective is at the focal distance from the sample? Simply, when we focus on the object and see it clearly this means that we are at the correct distance. As you can note, this is an instrument based on simple and effective solutions. What this microscope is missing is only the main body and the focusing device and in this article we will deal with their construction. |
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Figure 7 – On the left: binocular objective, on the right: |
Figure 8 – On the left: binocular objective, on the right: compact |
The philosophy that inspires this project is that of simplicity. Many parts will be realised with materials that are easy to find and work such as wood, plastic and aluminium. With these constructive solutions, this stereoscopic microscope model is particularly simple to build. Even with binoculars bought at a stall, you will obtain bright well-defined images. This stereoscopic microscope will be equipped with a single magnification of around 12 X and for its ease of use will also be suitable for children. As we will see further on, there is something that can be done to equip this instrument with higher magnifications.
If you are able to work metal, we have also prepared another microscope model with the same optics, but which employs metal for the focusing system.
COMPACT BINOCULARS
To construct this stereoscopic microscope, you must procure a pair of compact
binoculars (figures 2, 6, 7 and 8). In flea markets you can often find
compact binoculars that are sold at a low cost. It is also possible to purchase
compact binoculars in specialised shops, but at considerably higher prices.
When buying the binoculars, verify that the images are sharp and that the field is wide: in a stereoscopic microscope the field width makes the observations particularly striking. Verify that the binoculars don’t force you to keep your eyes so close to the eyepieces that it causes discomfort. It is important that the two objectives are for the most part contained within a diameter of 50 mm. Finally, the compact binoculars should stand up if you place them standing objectives-down on a level surface.
COMMON OBJECTIVE
You must procure an achromatic lens 50 mm in diameter and with a focal length of
approximately 200 mm. For this purpose, a normal binocular objective is fine,
provided that it has a diameter of at least 50 mm (figures 7 and 8 on the left).
It is possible to obtain lenses of this type from an old pair of binoculars that
are to be demolished or from binoculars bought at a low price from a shop or
stall. Verify that these binoculars have a clear vision and are not affected by
chromatic aberration or other types of aberration. As I have said, we will call
this lens: common objective. This will avoid confusion between the two
binoculars: the compact pair and the demolished pair.
ATTENTION! Binoculars that have objectives equipped with an anti-reflection treatment that is deep orange in colour produce images affected by an annoying dominant green that will alter the colours. Instead of these binoculars, use those with the traditional treatment which appears as a pale blue or violet colour.
MATERIALS (the measurements are in mm and are relative to my microscope)
1 pair of compact binoculars (see description
above)
1 common objective (see description above)
1 piece of wood or of black chipboard
18x180x200 in size (base)
1 strip of wood-coloured laminate to cover the edge of the wood
4 white rubber or felt plugs
1 piece of wood 20x50x360 (obtain a piece X-45 in length (see figure 9) for the
upright and another 50 in length for the carriage)
1 piece of wood 15x30x180 (ribbing)
1 plate of plexiglas or other hard plastic 15 mm thick (obtain two pieces of
30x50 for the supports)
1 tube of aluminium ø10x290 (obtain one piece 185 long for the guide and another
100 for the focussing bar)
1 aluminium tube ø12x40 1 mm thick (obtain two spacers to centre the focussing
bars)
2 plates of plexiglas 10x32x20 (for the supports to the focussing bars)
2 knobs ø 40
1 nylon-coated braided steel cable for model airplane construction ø 0.6 mm
1 plate of plexiglas 4x60x125 (support for the
common objective)
1 plate of plastic 10x20x60 (support for the common objective)
1 metal strip 1x10x130 (support for the common objective)
1 aluminium sheet 1 mm thick, dimensions to be defined (stirrup for the compact
binoculars)
2 solid plastic cylinders ø 15x20 (for the assembly of the objective carrying
plate on the carriage)
Screws necessary:
| TYPE | HEAD, drive | SIZE (mm) | QUANTITY | POSITION |
| wood screw | flat Philips | ø 4 x 45 | 3 | ribbing |
| wood screw | flat Philips | ø 4,5 x 45 | 1 | base (central) |
| wood screw | hex washer head | ø 4 x 50 | 2 | base (lateral) |
| large washer | øi = 4 | 2 | base (lateral) | |
| metal screw | button Philips | ø 3 x 25 | 4 | guide supports |
| medium washer | øi = 3 | 4 | guide supports | |
| set screw | hex socket, flat tip | M 3 x 5 | 1 | guide stop |
| set screw | hex socket, flat tip | M 3 x 5 | 2 | knobs |
| wood screw | slotted pan head | ø 3,5 x 35 | 2 | transverse bar supports |
| metal screw | hex socked cap | M 4 x 10 | 1 | inferior cable stop |
| little steel cylinder | obtain from a nail | ø 3 x 3 | 1 | inferior cable stop |
| ø 1 pierced plate | (to do) | ø 10 x 1 | 1 | superior cable stop |
| wood screw | flat Philips | ø 3 x 35 (o 40) | 2 | plate on carriage |
| metal screw | slotted pan head | M 3 x 10 | 4 | “V-shaped” support and strip |
| metal screw | hex socked cap | M 3 x 7 | 2 | stirrup |
WHERE TO FIND THE COMPONENTS AND MATERIALS:
Binoculars: market stalls or in specialised shops;
Aluminium tubes: hardware or DIY stores;
Piece of planed wood: DIY stores;
Flexible steel cables: model airplane shops;
Sheets and cuttings of plexiglas or other plastic: shops selling plastic
products, DIY stores, warehouses of semi-finished plastic, businesses that
produce plastic products (cuttings).
EQUIPMENT
To build this instrument, machine tools are not necessary. It is sufficient to
have some normal equipment for working wood, plastic and metals such as: a table
with a vise, an iron saw, some files, callipers, a square, a metal tip for
drawing lines, tap and die to thread M3 and M4 screws, tap wrenches, etc. It is
necessary to have a drill press equipped with a vise to grip the pieces to be
drilled. Given the large number of operations of assembly and disassembly
carried out during the construction of the body, it is useful to possess a
battery powered screwdriver. Amongst the files, a thin rounded file ø 3.5 a
rounded file ø 7.5 and a half round file. Amongst the squares it is also useful
to have a carpenter’s square.
MANUFACTURING PROCEDURE
In order for this microscope to function correctly, it is necessary to adapt the
various parts to each other during their construction. This task of adjustment
is important and the correct functioning of the focusing device depends largely
on this.
Before beginning manufacturing the parts, it is good to say a couple of words regarding the importance that the “grooves” can have. When you file a piece, it is normally necessary to obtain a flat surface. Particularly for those who do not have training in this type of work, it is easy for the final surface to result convex. This inconvenience can happen on the base of the upright-ribbing screwed onto the microscope base (Figure 10). To make this support column-upright stable, it is necessary to make a central groove using a file. This groove should make it such that this piece rests on the base on three surfaces (where the screws are). After tightening the screws, verify the perpendicularity of the upright with respect to the base using a square and if necessary file one or other of the surfaces until the upright is perpendicular.
The carriage can also suffer from the same problem, in fact, if the carriage or the upright on which it runs are slightly domed towards the centre, it will be difficult to avoid a certain oscillation of the carriage with respect to the guide. Instead, by realising a central groove on the surface of the carriage that runs on the upright, this problem can be avoided (Figure 15). You will have to adjust the height of the guide in order to allow the carriage to slide freely, but without oscillating. You can obtain this by lowering the supports or by gluing shims of paper under the carriage.
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DETERMINING THE MAIN DIMENSIONS OF THE MICROSCOPE How high should the column be? At what height should I mount the common
objective? Focus the binoculars to the infinity, focusing on a distant object. From here onwards, don’t touch the focusing device of this instrument. Place the compact binoculars on the common objective and with makeshift means fix these components at such a distance as to clearly see a minute piece of writing placed on the table. Now measure the height "X" as indicated in figure 9. Height of the column: Length of the guide: Height of the common objective: In Figure 9, the main parts of the microscope are summarised. The fixed parts (table, column, guide and supports) are coloured yellow; the carriage in red and the parts mounted on the carriage and which move with it are different colours. |
THE BASE
You can construct the base (figure 10) with a plank of wood. An excellent
solution consists in using a piece of chipboard with both surfaces covered in a
thin layer of black formica. Round the four corners. Along the edge of the base
apply a strip of laminated plastic (glued with mastic and then trimmed with
sandpaper). There is also a laminate available that is applied with an iron. On
the underside of the base and close to each corner fix a felt or rubber plug.
COLUMN
The column has the function of supporting the carriage and the optics. It is
obtained from a piece of wood reinforced with a posterior ribbing to increase
stability. The two pieces are screwed together and then to the base. With a
file, adjust the lower surface of the upright so that it is perpendicular with
respect to the base. If necessary, make a groove as indicated in the
“Manufacturing Procedure".
In reference to figure 10, the screw under the ribbing must have a flat head, while the two lateral screws under the upright must have a hex washer head and a flat washer. If, once the screws are fixed, the upright should result a little rotated with respect to the base, widen the two holes in the base for the lateral screws that fix the upright by a millimetre, mount and tighten a little the flat head screw, then with the square orientate the upright and tighten the hex headed screws with the washer. In this way, you can correct the error in alignment.
FOCUSING SYSTEM
This solution is suitable for whoever knows how to work wood and is particularly
simple to realise.
In this system we can distinguish three parts: 1 - guide, 2 – carriage,
3 – focussing device. The carriage moves along the guide and is moved
by the focussing device (Figure 12).
GUIDE
The guide consists of an aluminium tube 10 mm in diameter and is fixed to
the upright by means of two plexiglas supports (Figure 12).
In order to reduce parallelism errors between the guide and the upright to a
minimum, make the hole on both of the supports while keeping them superimposed
and held tightly in the grip of the drill press. Fix the supports to the wooden
column using M3 metal screws (figure 12). On the upper support also make a
threaded M3 hole for the screws that stop the guide (Figure 15/1).
CARRIAGE
The carriage is formed from a block of wood cut from the same piece from which
you obtained the upright. Clearly, the holes for the guide must be at the same
height on both the support and on the carriage. Verify that the carriage slides
freely. If this does not happen, you must file the supports or the carriage, or
apply shims.
To avoid the carriage having rotating movements such as those of a door on its hinges, this must slide against the wooden base. As I have already indicated, it is useful to make a longitudinal groove on the surface of the carriage that is in contact with the column (figure 15). At this point, the carriage should slide quite freely when you move it with your hands.
FOCUSSING DEVICE |
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Figure 11 – Support with a |
MOUNTING THE STEEL CABLE
After taking the necessary measures, make holes in the upper and lower supports
of the guide to allow the passage of the cable (figures 14, 15 and 16). These
holes, with a diameter between 1 and 2 mm must be positioned so that the cable
remains parallel to the guide. Remember also that due to the winding of the
cable, the upper and lower holes must not be coaxial, but moved by a few mm. In
figures 14 and 16, you can see the path of the steel cable.
In the lower support, make a threaded M4 hole to fix the cable (figures 14 and 16). Cut a piece of cable approximately 50 cm in length and make a knot at one end. As indicated in figure 15, pass the cable through a small metal washer with a hole small enough to prevent the passage of the knot (figure 15) and pass the cable through the hole in the upper support. Wind the cable around the transverse bar four times, keeping the coils closely together side by side. Pass the cable through the lower support, pulling it with a couple of kilograms of force, move the knobs a little and tighten the stopping screws. If necessary, repeat the tightening of the cable. If the cable is tightened as it should be, by turning the knobs, the carriage should rise without sliding. To increase the cable tension, before mounting it, loosen the two screws in the upper support. In this way, the support will lower a little. When you have tightened and fixed the cable, tighten the screws of the support and the cable will be further tightened.
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The stopping screws of the cable press the steel cable against the plastic of the lower support which tends to give way. To improve the hold of this stopping device, deepen the hole with a 3.2 mm point and insert a metal cylinder with a diameter of 3 mm and of such a length that the cable is blocked without undergoing significant deformation. You could obtain such a cylinder from a nail with a diameter of 3 mm. Level the point of the stopping screw and the surface of the cylinder in such a way as to not damage the cable when it is blocked. To avoid it pricking the nose of the observer, the cable is inserted in the hole of the guide or in a hole made specifically in the upper support. The lower end of the cable can be inserted through the hole of the guide. This end must be longer to consent the tightening of the cable by hand. |
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Figure 13 – The focussing device is
composed of a |
Figure 14 –After mounting the flexible
cable, the |
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Figure 15 – Upper support. Note the screw (1) that hold
the guide |
Figure 16 - Notice how the focussing bar and the |
MOUNTING THE COMMON OBJECTIVE
As I have already said, you can obtain an excellent common objective from a pair
of binoculars. This objective must have a diameter of 50 mm. Detach one of the
objectives from the binoculars and mount it with the lens facing upwards as
indicated in figures 17, 18 and 19. In this way, the objective should have its
axis parallel to the plate.
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Fix the plate that carries the common objective to the carriage. Two cylindrical spacers carry the plate at a distance of some mm from the upper support (figure 17). Verify that the objective is also in axis in the right-left sense.
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Figure 18 – Support for the common objective. Below: |
Figure 19 – Common objective mounted on the carriage. |
MOUNTING THE COMPACT BINOCULARS
Now, there remains to fix the compact binoculars on the common objective. Place
the compact binoculars on the lid of the common objective and with a pencil
trace around the edge of the objectives. Within this outline, make two holes 20
mm wide to allow the passage of light. The width of the holes must allow the
binoculars to be narrowed when the microscope is used by children.
If you place the compact binoculars on the lid of the common objective, you can already use the microscope, but only a small knock is sufficient to make the binoculars fall. Therefore, make a stirrup like the one indicated in figure 19 or another system to prevent the binoculars from falling.
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If you tend to see the images doubled, try applying a diaphragm of black card with a hole 14 mm wide to allow the passage of light in front of each objective of the binoculars, as illustrated in figure 20. COMPLETION |
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MAGNIFICATION OF THE MICROSCOPE
To calculate the magnification of the microscope, you can use the following formula: Im = 250 x In/Fd
where:
Im = magnification of the microscope
250 is the conventional reading distance (in mm)
In = nominal magnification of the compact binoculars
Fd = focal length of the common objective (in mm)
Using a pair of 8 X compact binoculars, if Fd = 190 mm, you will have:
Im = (250 x 8)/190
Im = 10.5 X
If instead you use a pair of 10 X compact binoculars, the magnification of the microscope will be 13 X.
How do you determine the focal length of a lens? Place the lens between a lamp and a screen. Focus the lamp on the screen. Determine the distance from the centre of the lens to the lamp (distance A) and that from the centre of the lens to the screen (distance B). Thus, the focal length will be:
F = AxB/(A+B)
VARIATION OF THE MAGNIFICATION
It is possible to equip the microscope with a second magnification. For this
purpose, you must be able to mount a second achromatic objective under the
first. This second lens can be taken from the same binoculars from which you
obtained the first and can be placed beneath the first with a “flag” movement.
When the two objectives overlap, you will obtain a double magnification. To have
a clear image, these two lenses must be well centered with each other. A solution
which permits you to obtain a clearer image is that of not overlapping the two
objectives, but to look first with one objective and then with the other which
has a shorter focal length than the first. If the second objective has a focal
length half that of the first the magnification that you obtain will be double.
A third method for obtaining a variation in magnification consists in using
compact binoculars equipped with zoom. This type of binoculars is available on
the market, even without the orange anti-reflection treatment.
Before using the microscope, regulate the interpupillary distance of the compact binoculars for your eyes. Focus the binoculars to the infinity. To do this, focus the compact binoculars on a distant object. At this point, place the compact binoculars on the common objective of the microscope and begin your observations. To focus on the samples that you observe, use always and only the knobs on the microscope. If another person wants to use the microscope, regulate the interpupillary distance, taking care not to touch the focusing device of the compact binoculars which must always remain focused to the infinity.
Take a piece of black, a piece of white and a piece of grey card. Place the samples to observe on a piece of card, which will also be useful to move the samples during observation. Normally, dark samples are viewed on a pale background and vice versa. The microscope is sufficiently bright to use in natural light, but particularly in the evening it is useful to have a lamp or a spotlight to adequately illuminate the sample.
A direct light such as the sun or a spotlight exalts the plasticity of the subject, creating a nice play between light and shade, but tends to increase the contrast of the image. If, instead, you prefer to observe the finer details, you will need to use diffuse light. You can transform sunlight into diffuse light using a sheet of paper or translucent plastic placed in such a way as to intercept the light that arrives. A strip of white paper placed behind the sample can improve the diffuse light conditions. Another method for obtaining diffuse light consists in using a neon toroidal lamp placed under the common objective. Furthermore, you can try to create conditions of intermediate light, directing the light from a spotlight in an appropriate way by partly reflecting or diffusing it.
If the microscope will be used by children, put it on a low table or on a bench so that its young users can easily reach the eyepieces.
Pay attention that nobody touches the lenses, otherwise fingerprints could blur the images. Clean the lenses as little as possible. Don’t worry if there are dust particles. If you want to remove these, use a soft paintbrush. If it is necessary to clean the lenses, first remove the dust using a paintbrush and then clean the lenses with a piece of damp cotton, or with a piece of suede. Never use normal paper, but only special paper for optics. In fact, mineral powders are inserted into normal paper which would scratch the surface of the optics ruining them. Paper for optics is instead made from pure cellulose. If there are fingerprints on the lenses, remove them with a piece of optics paper dampened with alcohol, then pass a dry piece or a piece slightly dampened with water over them, so that halos do not remain.
When you have finished using the microscope, cover it with a plastic bag to protect it from dust and place it in a box. In the same box you can place the compact binoculars closed in their case, instruments such as a pair of tweezers, a small knife, a Petri dish, small boxes and jars with lids to keep samples in, a dropper, pieces of black, white and grey card etc. Here you can also keep the instruments necessary to regulate the microscope such as screwdrivers and Allen keys. Keep a reserve of steel cable to repair any breaks in the mounted one. Put the box in a safe place. If, instead, you would prefer to display the microscope that you have constructed, keep it on a cabinet, covering it with a transparent bag or even better with a plexiglas cover.
What can you observe with this microscope? Look at flowers,
insects, minerals. In some articles in this guide, you can find suggestions on
what to observe:
http://www.funsci.com/texts/itom.htm
HOW MUCH WILL THIS MICROSCOPE COST?
- 20 euro for the binoculars to disassemble (with these you can construct
2 microscopes);
- 15 euro for the compact binoculars (as these binoculars can also be used as
normal binoculars, this expense does not have to be considered);
- approximately 10 euro for all of the pieces of wood and plastic. You will
certainly have enough pieces left over to make at least another couple of
microscopes;
- 5 euro for the aluminium tubes, which are 2 metres in length and you will use
300 mm of the one 10 mm in diameter and 40 mm of the one 12 mm in diameter;
- 4 euro for the knobs;
- a couple of euro for the screws;
- finally 5 euro for the steel cable 10 metres in length.
If we calculate the total cost, you will spend 66 euro;
If we deduct the cost of the compact binoculars, you will spend 51 euro;
If we consider only the cost of the various materials and components used in the
construction, you will spend approximately 20 euro.
Can a quality stereoscopic microscope be bought for less than this? I don’t
think so! :-)
Here is another stereoscopic microscope that is easy to construct! As you have seen, even the construction of the microscope body and the focusing system is simple to do. The apparent difficulty is due to the fact that it is hard to explain these things in words, while they would be much easier to demonstrate. Even with little expense, the optical quality of this microscope could be very good, certainly superior to that of commercial models aimed at the amateur public. Retired grandparents, why wait to give your grandchildren an instrument made with your own hands that they can keep and treasure? I await the photos of you standing beside the microscope that you have just built! I also await your comments on the functioning of this instrument.
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