Edmund Scientific's Popular Science Library 2 - Science Gifts

Edmund Scientific's Popular Science Library 2

(From Edmund Scientifics Collimators and Collimation (30090-72))

COLLIMATING BY EYE. One popular method of collimating a binocular is based on the fact you can look slightly cross-eyed in perfect comfort. On the other hand, it is difficult to look up with one eye and down with the other. So, knowing your eyes can readily accommodate for convergence, you set both objectives for maximum convergence and then confine actual collimation to the up-down movement. The target is any level line object, such as a window sill. It is best viewed at short range. Put the binocular on a support. Be sure both eccentric rings work freely. Have both thin sections together, and to the outside in each barrel. In such position, the initial rotation of the eccentric ring is almost pure up-down movement. Keep your eyes 6 or 7 inches behind the binocular to make image movement more apparent. The long eye position will produce the characteristic double-0 view, but this does not affect the accuracy of the collimation. The whole idea, of course, is to make the horizontal target line continuous. With close target and long eye position, this can be done with surprising accuracy--even 1/32 inch movement of the eccentric can be seen to produce a definite change the position of the target.

PRISM ROTATION. Prism rotation or tilt is easily detected by looking through one barrel of the binocular at a time, allowing the free eye to see the target at the same time. The two views are seen superimposed. If the prisms are properly adjusted, vertical lines will be perfectly parallel. The proper adjustment of each pair of binocular prisms is that they must be exactly at right angles to each other. Any departure from 90 degrees will introduce twice the amount of tilt invertical lines. This would be an easy fault to correct if it were not for the fact you usually have to disassemble the whole optical system to do it. Sometimes you can make a correction with one prism only, and this can sometimes be done without removing the prism shelf from the binocular. Usually you will end up by removing the whole prism shelf. The test is made just as readily with prisms alone, and the rules for adjustment are the same.

A SIMPLE BINOCULAR COLLIMATOR. Of several methods used in professional binocular collimation, the simple collimator and sighting telescope setup is the most common and also the easiest to make and use. The pros prefer twin collimators and twin sighting telescopes to reduce the actual work of collimation, but you can get along nicely with single collimator and single sighting telescope. A typical rig is shown in Fig. 11. You can build it in one evening for cheap, assuming you already have a few of the parts (eyepiece and machine vise). The sighting telescope should be low power, not over 3x. The holder for the telescope should have a tilt adjustment, as shown.

The collimator lens is an inexpensive achromat, 7 inches f.l. The reticle target is drawn with a fine pen on tracing paper. A circle 118 inch diameter indicates maximum range of adjust- ment; the larger circle shown is simply a general guide and can be any diameter. The illumination can be obtained from a window (in daytime) or from any kind of table lamp or light bulb.

The eccentric rings and objective cells of the binocular must rotate freely. Quite often the main job of work in collimating a binocular is simply the business of getting the parts loose enough to turn. A tubular wrench is a great convenience in turning the eccentrics. Lacking this, it is permissible to drill small holes not over .031 inch (No. 68 drill) in which wires can be inserted.

The equipment is made ready by centering the sighting telescope on the collimator target, that is, the cross-threads of the sighting telescope are centered exactly on the crossline of the collimator target. To do this you can shift or tilt the sighting telescope as desired. There should be no visible parallax in the sighting telescope, which means the cross-threads should stay put on target as you move your head from side to side. After the proper centering is obtained, the wood guide strip is clamped in place alongside the sighting telescope holder. Recheck to see that the sighting telescope is still on target. Also, push the sighting telescope along the guide and you will note that the sighting telescope remains centered on the target. In other words, the sighting telescope does not have to be directly behind the collimator--it can be at any position so long as it picks up a good portion of the light. The same is true when the binocular is faced into the collimator--all you have to do is get it somewhere in the beam.

You start collimating with both binocular objectives centered in their eccentric mounts. Place the binocular in the holding fixture and clamp it securely. Face one objective toward the collimator. Focus the binocular eyepiece on the collimator target. Slide the sighting telescope behind the binocular eyepiece. Now, your line of sight is through the sighting telescope, through the binocular to the collimator target.

Shift the binocular as needed to put the sighting telescope reticle anywhere within the I degree circle on the collimator target; if a tilt adjust- ment is needed, it is obtained by loosening the vise and then reclamping the holding fixture. After a satisfactory line of sight is obtained, the guide strip of wood is clamped to the base- board alongside the machine vise. Everything about the setup is now fixed and the only adjust- ment vou can make is at the eccentric rings. You must be especially careful not to disturb the position of the binocular whi)e manipulating the eccentric rings.

If the initial sighting shows both barrels of the binocular well within the 1 degree target circle, you are assured that the binocular can be collimated. This is what you proceed to do, adjusting each objective until the crossthreads of the sighting telescope intersect exactly the crossline of the sighting telescope intersect exactly the crossline of the collimator target. Check frequentlv to see if the sighting telescope itself is still centered exactly on the target. Be sure to maintain contact when you slide either the machine vise or the sighting telescope along its wood guide strip.

If a prism rotation adjustment is needed, thi must be done first before you can collimate. The rotation is easily checked on the binocular collimator by rotating the collimator until one of the target lines is approximately vertical. The sighting telescope reticle is then made parallel with the collimator target. Then, putting the binocular in place, any non-parallelism of the target lines indicates the prism angle is in error.

Do not be in too much of a hurry to make prism adjustment; if both barrels are tilted but in the same direction, the binocular will work satisfactorily and you will not notice the slight tilt of the view.

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Build Your Own 30X BABY Refractor

(From Edmund Scientifics Telescopes You Can Build (30090-65))

THE BABY of the astronomical telescope family is a refractor with a 1- 1/4 inch objective. A small object glass like this will show stars to 9th magnitude; it is swell for the moon and bright planets, but poor for dim sky objects. With 1.05 inch focal. length eyepiece, the power is an even 3OX, enough to show a wealth of moon detail and the ring around Saturn. The image sharpness is excellent. With a Ramsden eyepiece, the field is a comfortable 70 minutes of arc or a little over the width of two full moons. With a field this size in a small refractor, you can get along fine without a finder.

This is a cardboard-and-wood job and is easy sailing providing you have a wood lathe. The focusing tube is a length of Reynolds craft aluminum. For a mount, the simple clamp-on-altazimuth shown can be clamped to any garage door, fence post.- etc. The hose clamp is a geared type used in the assembly of plastic drain pipes --you can buy at most hardware stores and plumbing stores.

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Build A Solar Furnace

(From Edmund Scientifics Fun With Fresnel Lenses (30090-53))

You can make a simple solar furnace with a single Fresnel lens mounted in a wooden frame as shown in Fig. 2. CLICK HERE TO SEE ILLUSTRATION. The base consists of a piece of 1/2" thick ply-wood with rounded corners. The U-shaped frame is made out of 1 x 1- 1/ 2" wood (these dimensions are not too critical). The frame stands 18" high and is 15-1/2" wide. Drill a hole in the bottom part of the U to pass a 1/4" bolt and wing nut. The two arms are slotted at the top to accept 1/4" bolts and wing nuts which project from the mid-point of the frame.

The frame which holds the Fresnel lens is out of the same stock used to make the U-shaped frame. Cut a groove in the middle of the four pieces of wood which make up the frame to accept the Fresnel lens. The outside dimensions of the frame measure 13-1/2" x 13-1/2". The groove cut into the wood should be deep enough to accept about 1/4" of the Fresnel lens all around its periphery. Before inserting the Fresnel lens into the frame, drill two holes at the mid-point of two of the frame sections. Through these holes pass two 1/4" bolts. These bolts, tightened with wing nuts, form the axis which will allow you to tilt the Fresnel lens up or down so that it will be perpendicular to the sun. The wing nut assembly at the bottom of the base will allow you to shift the assembly from left to right.

The next step is to insert the lens into the frame grooves. Use glue and brads to secure the four pieces of the frame together. You are now ready to give it a try. Crumple up a sheet of newspaper, point the lens at the sun, and Io and behold ... the paper will burst into flame. Be careful. You are in effect, concentrating a disk of sunshine 13" in diameter into an area less than an inch in diameter.

The final step in the construction of the solar furnace is the mounting of the L-shaped bracket that will hold the crucible. This bracket, also made out of the same stock used for the construction of the furnace, is fastened in place with two round-head screws to the bottom of the frame holding the Fresnel lens. The length of the bracket is determined by the focal length of the Fresnel lens --- and with allowance for the height of the crucible.

The crucible can be made out of ordinary firebrick, a good grade of ceramic or you can buy a small crucible from a supply house specializing in products for chemistry college classes.

When you set up the furnace, make sure that the crucible is in place, other-wise you will char and burn the bracket. This furnace will develop a temperature of 2,OOOOF, so be careful. Do not look directly at the projected image of the sun...wear dark glasses, if you must. This hot spot is as bright as the arc in a welder's torch ... and he always wears dark glasses

The solar furnace can produce some unusual jewelry. At about 1,5000F, powdered enamel will fuse to metal, but since some enamel colors reflect and absorb heat more than others, you will get some really exotic effects because of the difference in melting rates. You can watch this operation through dark glasses.

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Build Your Own Grating Spectroscope

(From Edmund Scientifics Fun With Optics (30090-50))

FEW OPTICAL instruments can be made as cheaply as a grating spectroscope--all it takes is a plywood or cardboard box and a piece of diffraction grating in cardboard redimount. Although low-cost, the performance is excellent, surpassing in some respects the more expensive prism spectroscope.

A lensless spectroscope needs a box or tube 12 or 13 inches long, as shown in Fig. 1, with the grating taped or tacked to one end and the slit similarly mounted at the other end. A good slit width is about .015 inch, equal to the thickness of three or four sheets of paper. Fit the grating last; a quick look-and-see will tell you if the grating lines are parallel with the slit as they should be.

By far the best object to look at with your homemade spectroscope is a fluorescent lamp. This will show a continuous color spectrum from the light of the lamp itself, while mercury and argon inside the tube reveal their presence with characteristic bright lines in green, orange and blue-violet. Salts of many elements are readily available and their spectra observed by vaporizing solutions in the flame of a torch. Sodium, Fig. 3, is popular since sodium chloride is ordinary table salt.

What you see in any spectroscope is a multiple image of the slit. This means the slit itself must be in sharp focus, hence the 12-13 in. length of the lensless model. If you want a shorter spectroscope, all you have to do is use a lens to shorten the viewing distance. Any simple lens from about 4 to 6 inches focal length will do nicely. Fig. 4 shows a simple type of contruction with fixed slit and fixed focus. Figs. 5 and 6 detail an improved pocket spectroscope whiel provides for focusing and adjustment of slit width. Optional in either model is a glare stop to eliminate stray light; the offset eyehole is fo same purpose. Slot in focusing tube is needed to keep grating lines parallel with slit.

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How Diffraction Gratings Work

(From Edmund Scientifics The Edmund Diffraction Grating Idea Book (30090-64))

The grating film is a colorless plastic material containing 13,400 parallel grooves to the inch. A microscope is required to see these grooves.

We shall discuss three terms: White light, diffraction and interference.

White Light such as we receive from the sun is described in the physical sense as being composed of all spectral colors. You may be familiar with how a prism or diffraction grating will separate this light into its components. The red end of the spectrum contains the long wavelengths; violet the short wavelengths.

Diffraction is the term used to describe the action upon a beam of light when it passes over a sharp edge or through a fine slit. We are here interested in the slit. The central ray will pass through undisturbed. The light grazing the edges will be deviated from the normal. If we examine the pattern thus produced we will note a central white band and to either side, a series of spectra. The violet end of the spectrum will be nearest brightest with each complete spectrum becoming progressively dimmer. This experiment would require rather precise conditions to be successful. The deviation of the light is the effect of diffraction. The formation of the spectrum is the effect of interference.

Interference is best explained by analogy: in a calm pond drop two pebbles some distance apart. Each will act will start a series of radiating waveforms. Several points of intersection will occur. The coincidence of two crests will create a point of extra height; one crest and one trough will create a mean and two troughs will produce a point of extra depth. In short, a pattern will be produced wherein energy is apparently reinforced, averaged and cancelled. CLICK HERE TO SEE ILLUSTRATION

Our grating may be regarded as thousands of slits, evenly spaced and parallel to each other. We will assume that light is behaving with the same wave action as we described in the water analogy. If a wave front strikes the grating, each slit will become the emitter of a new "wavelet". Each slit will also diffract the ray passing through it. The wavelets will spread from the grating, intersecting and creating points of reinforcement, neutralization and apparent cancellation. Since we are using white light the nature of the wavelets will be complex. All spectral colors are present. Along a line connecting the points of successive reinforcement, a bright, continuous spectrum will be seen. These spectra will be repeated in order with some overlap and rapidly diminishing brightness.

Types of Gratings

Transmission Gratings This is a transparent acetate film material that has been embossed with 13,400 grooves to the inch. To see a beautiful spectrum simply hold a small piece up to your eyes and look through it. This can be done with larger panels. If a sheet is placed on a window, etc. through which the sun is shining a spectrum will be thrown on the floor, wall or ceiling and be very pleasantly visible if the room is reasonably dark.

Reflecting Gratings This type is of the same material as the transmission type, except a thin, coating of aluminum has been deposited on the grooved side in a vacuum chamber for reflecting the colors. Held close to the eyes you will see that it is approximately 10% transparent like a one-way mirror. This type lends itself beautifully to areas where you want the spectrum reflected back at you.

Viewing And Handling Seeing the lines of grating is impossible with the unaided eye. And because lines of grating are responsible for the beautiful color effects, you may wish to see exactly what you are working with.

Seeing the highly precise embossed lines of grating is readily accomplished with a microscope having a power as low as 30OX. 900 power enables you to see them quite easily, while 600 power affords a very convenient workable power for the observation of these lines.

The above holds true for both the transmission and the reflecting types of grating when properly lighted. However, the reflecting type presents a much more attractive field of view and the lines are more discernible.

Suggestions

CLICK HERE TO SEE ILLUSTRATION

Heat Test Results

The acetate film material holds up quite well under heat as you will see from the following test results. Transmission type grating was used only in the test but it is indicated that reflecting type will be affected in the same manner. Also, the material will burn only under direct flame application.

Our research into the damage caused by heat (and moisture) continues and the following results (Fig. 2) are given only as indications of the gratings heat resistance. It may be desired to use the warping or malforming in the manner described in the section dealing with Random Panels. CLICK HERE TO SEE ILLUSTRATION

These tests were conducted in a standard temperature adjusting industrial oven (Grieve-Henry, 220 volts, 3 kilowatts, 1 phase, 50/60 cycles).

The lens of grating will of course be affected by the warping of the acetate material. However, color was still visible on the grating even after the 275 degree exposure.

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How To Find Sky Objects

(From Edmund Scientifics How To Use Your Telescope (30090-55))

CLICK HERE TO SEE ILLUSTRATION
VARIOUS methods are used in locating sky objects with a telescope, ranging from coarse naked-eye sighting to precise pin-pointing with the use of setting circles. All methods require a good mount--it must not vibrate unduly, it must "stay put" at any position and it must work smoothly on both axes. Other'requirements are a planisphere and a star atlas. The planisphere is used to determine the general aspect of the sky; the atlas then supplies the detail maps. Don't expect to find sky objects by random sweeping--you must know exactly what you are looking for and how to get there.

STAR HOPPING. This is the finding method most used by beginners. The idea is that you hop from a bright star you know to another star you know, etc., and in this way reach your target, which may be invisible to the naked eye. An important part of this technique is careful plotting of the course on a star atlas. Make a "field plotter" of clear plastic as shown in drawing, scaled to the degree marks which you will find at the edge of all atlas maps. If you don't know the field of your finder, find it by the method shown in boxed drawing below.

Now, let's plot the route to a typical telescope object, such as M 11. Altair will be your pilot star or starting point. Note in the drawing that a 6-degree finder field will take in the two guard stars, which will make identification positive when you locate Altair in the sky. Move the field plotter, keeping Altair in field but stretching out to another star along the route. This will be Mu, as shown. Keeping Mu in the field, you can reach Delta. From Delta to Lambda you will have a little bit of blind hop, but it will not be hard to pick up the curved string of stars ending at the top of Scutum (SKYOU-tum), the Shield. Below Eta and Beta in Scutum you will find three faint stars, and about half degree east and south is M 11.

Note that the general direction of your route is west and south. The drawing shows the stars as they appear in a naked-eye view facing south. If your finder is the usual inverting type, all this will be upside down. Hence, turn the drawing (or atlas) upside down and it will then agree with the view you will see later in the eyepiece of the finder. Memorize each step of the route; call out each star by name. Careful attention to the atlas plotting will make the actual finding of M 11 a fairly simple matter. It will show as a misty patch of light in the finder, while the telescope will resolve it into a myriad of tiny sparklers.

RIGHT ANGLE SWEEP. With an equatorial mount there are just two possible movements: (1) Any movement on the declination axis will follow a meridian, (2) any polar axis movement describes a circle around the pole. These movements are at right angles and correspond to the grid of lines shown on all atlas maps. In making a right angle sweep you first locate a pilot star and from this step off the required number of degrees in two separate movements, measuring the distance by the field of a low-power eyepiece. The finder is not used. CLICK HERE TO SEE ILLUSTRATION

M 39 is shown as a target object, with Deneb the pilot star. You will need a little cardboard scale, marked to atlas scale. This serves to measure angular distances in both declination and right ascension. The scaling is not exact on most maps, especially for the crosswise R. A. distance, but is accurate enough for the purpose.

As shown in the drawing, M 39 is 3 degrees north of Deneb and 8-1/2 degrees east. A low-power eyepiece with a field of about 1-1/6 degrees (the average) is convenient for stepping off the distance, the slightly larger field eliminating the need of measuring exactly to the edge of eyepiece field.

Make the declination sweep first. You will be able to see many faint stars not shown on the atlas and these serve as spacing guides--you pick up any star at one side of the field and then move the telescope to put it at the opposite side--that's one field or 1 degree. After completing the declination step, lock the declination shaft. Step off 8-1/2 fields to the east, moving only on the polar axis. This should bring you to M 39. If not in the field, sweep cautiously in the immediate area--M 39 is just a bright splash of stars and is not outstanding against the rich background of the Milky Way.

In any right-angle sweep, it will be apparent you have a choice of two routes. Sometimes a convenient bright star will simplify the whole operation, is as with M39, the alternate route shown has a turning point at Rho, eliminating the need of measuring the angular distance. While in the Cygnus area, stars Deneb and Delta provide a convenient check for the alignment of your mounting to the pole--you should be able to sweep from one star to the other with polar axis movement only. The separation of 10 degrees can be used to check atlas scale and also your own ability to step off the distance with eye- piece field.

SWEEPING IN SAGITTARIUS. The Sagittarius region was Messier's favorite hunting ground and more than a quarter of his popular list can be found in this richly-spangled area of the sky. Sagittarius is especially good for measured right-angle sweeps, using reddish, third magnitude Lambda as a pilot star. A little triangle of stars directly under Lambda will make identification positive. If you put Lambda at the edge of a low-power field you can pick up a faint glow at the opposite edge of field. This is the globular cluster, M28, of seventh magnitude. A brighter globular is M22, which tops the famous M13 cluster in size. CLICK HERE TO SEE ILLUSTRATION

If you move 1 degree north from Lambda in declination and then sweep to the west in R.A., you will not fail to pick up M8, the popular Lagoon nebula. It is unfortunate this splendid object must be viewed under the luminous skies of summer, since even this small amount of light destroys the nebulosity which forms the lagoon, leaving only a fair star cluster. View this on a really dark night about midnight and you will understand how it got its name--it does indeed resemble a misty lake dotted about with lights.

There are many fine open clusters in Sagittarius, all easily located with measured sweeps from Lambda. M25 and M23 are popular low-power fields; M24 packs about fifty stars in a tiny 4-minute field and needs a 3 to 6-inch objective and medium power for good resolution although the bright glow of about fifth magnitude is easily seen with the smallest telescope or binoculars. Sagittarius offers a good test sweep from Zeta to Delta of nearly an exact nine degrees separation and on nearly the same parallel of declination. Zeta is a fine double (mags. 3.4 and 3.6) but the separation of less than 1 second puts it beyond the range of most portable telescopes.

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Shooting A Star Trail

From Edmund Scientifics Photography With Your Telescope (sku))

A STAR TRAIL is made by pointing any fixed camera at any part of the sky and exposing for 10 minutes or more. The stars, of course, keep moving right along, making a pattern of light streaks. CLICK HERE TO SEE ILLUSTRATION

One common difficulty is field coverage. The average camera has a field of about 50 degrees. This means that if you center on Polaris, the half-field angle will reach down to about 65 N. declination, not quite reaching the Dipper. One way to capture the Dipper is by putting Polaris at one corner of the film, as shown in photo. This is a 25 min. exposure on 5x7 Tri-x film, using a 6-inch Metrogon lens at f/5.6. The bright streaks at top left are the Dipper stars.

Sky fog is another problem. Every minute you expose, the sky background becomes lighter. In 3 hrs. or so, sky fog may washout the star trails. There is no simple solution to this except the obvious one that if you make a short exposure, the sky will stay black. The photo insert shows the Dipper stars as seen with a twin lens reflex working at f/4.5 with Tri-x film, the exposure being 2 minutes. Big star images were obtained by putting them slightly out of focus. One way to tackle sky fog is to make the trails brighter.

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Build Your Own Low Power Microscope

(From Edmund Scientifics Popular Optics (30094-45))

CLICK HERE TO SEE ILLUSTRATION

THE SIMPLE magnifier has a top power of about 20x. Beyond this you need double-header or compound magnification, which is the lens system of the microscope. The front lens or objective forms a magnified image by simple projection, and the second lens or eyepiece further magnifies the magnified image. The total magnification is the magnification of the eyepiece.

Most professional microscopes have a top power of about 1500x although up to 3600x can be obtained. Good-quality student microscopes go 900x; junior or toy microscopes are good to about 450x. 300x is plenty of power if you want a microscope for fun and experiments; 40x or 50x is the best choice to see a wide field.

You can easily make your own low-power microscope, as shown in the drawing. It can be used as a pen microscope held in your hand, or it may be mounted on a stand with 45-degree mirror to reflect light through slides placed on the stage. The construction shown calls for turning a piece of wood on the lathe; some turning may also be needed on the bottle caps which hold the lenses in place.

You can also do the job with telescoping cardboard tubing. If you use telescoping cardboard tubing, you can vary the power by changing the tube length-the longer the tube, the higher the power. If you want a more powerful microscope, it is best to use a shorter focal length objective rather than a stronger eyepiece. Two identical plano-convex lenses in contact will make an objective of twice the power of the single lens.

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