WILLIAM M. SINTON, a graduate student in physics at The Johns Hopkins University, is responsible for the weird photographs on the opposite page. Removing the normal lens from his camera, he inserts in its place a simple hemispherical lens that he made on his own bench. It yields these extraordinarily wide-angled pictures. The human eye can see clearly over an angular field of 20 degrees at one time; common cameras photograph 50 degrees; those with wide-angle lenses take in 90 or more degrees; but Sinton's lens photographs a full 180 degrees-the entire hemisphere in front of it. The lens will photograph at one time three walls and the whole ceiling and floor of a room. At a street intersection it will photograph down three of the four streets and from the ground at the foot of the camera tripod clear up to the zenith. Pointed straight up, it will photograph the entire dome of the sky down to the horizon all around.

Standard camera lenses are composed of a number of separate lens elements, each of a different kind of glass with different curvatures, to minimize optical aberrations. But the Sinton lens, which we may call the "Sintar," is made of a single element, which an amateur can produce in a few evenings at a kitchen table, using only a dollar's worth of glass and very little equipment. The catch is that the Sintar lens reeks with optical aberrations. However, instead of bemoaning these, Sinton has fun with them. His is quite frankly a trick lens for taking distorted photographs. He; writes: "One of the photographs, taken with a camera held close to my forehead, shows me as a highbrow; another, taken close to my nose, leaves me a lowbrow; as in true life, it is all in the point of view [see photographs].

A photograph along a colonnade on the Johns Hopkins campus shows the distant end little distorted and the columns and steps increasingly curved closer to the camera. A photograph of the entire campus made from a captive balloon 300 feet aloft makes the University look like a spherical "asteroid" in space. "I would like to put the lens on a V-2," says Sinton, "and photograph the earth from 100 miles aloft. The photograph would include most of the U. S. and the earth would look like a planet.

"The hemispheric lens," he continues, "has three major aberrations. The first is barrel distortion, which makes a rectangle look like the outline of a barrel. The effect is well shown in the view from the balloon, in which the rectangular pattern of the campus paths is changed to the outline of a barrel. The second aberration is curvature of field, due to the fact that, while the lens focuses the rays on a spherical imaginary surface in the space behind it, the film is flat. This aberration is tolerable if the lens is given an aperture no larger than f/32. The third aberration is lateral chromatism. Light rays entering the glass near the edge of the field of view are bent slightly differently for different colors and fall in different places. This aberration, which cannot be diminished by stopping down the lens, may be reduced by narrowing the wavelength range with a filter."

Barrel distortion and curvature of field are illustrated in the photograph of a straight brick wall which seems to bulge like a balloon, and of a building and sidewalk which appear to thrust their middle toward the camera. The silhouette of the photographer and his camera tripod is visible in each of these photographs. Sinton comments: "With this 180-degree lens one could get both the sun and his own shadow in the same photograph."

The Sinton lens is not merely a freak but had scientific origins. Half a century ago the Johns Hopkins physicist R. W. Wood set out to learn how the world looks to a fish. He published a paper describing his experiments in The Philosophical Magazine in 1906. Says Sinton: "The fish is able to see everything in the whole hemisphere of sky and landscape above the water, because the refraction of the water surface crowds the hemisphere into a cone having an apex of only 97.2 degrees. By putting a plate and a lens in a bucket, Wood recreated a fish's field of view. In an improved model he substituted for the lens a pinhole scratched in a piece of mirror glass which was cemented, glass side out, over a hole in the end of a watertight box. It had a watertight cover which could be opened for loading the camera in the dark room. The camera in this set-up could be pointed in a horizontal direction, because it was watertight. Wood's exposure time for these pinhole cameras was about one minute in bright sunlight.

"I made one of Wood's improved cameras and took pictures with it but wearied of loading the wet, mussy thing in the darkroom. I then hit upon a way to do away with the water, at the same time having a lens in the air, where it could refract the light. This in turn would permit a higher relative aperture than a pinhole affords and reduce exposure time while increasing resolution. The design would have a large glass diaphragm to support and position the attached hemispheric lens in the center of the metal lens mount. The diaphragm would be painted black, with a small f/32 hole scraped in the center. The incoming rays would be refracted at the front surface of the glass-a typical plate glass having an index of refraction of 1.525. The angle of refraction of the rays shown would be about 82 degrees. The rays would pass through the aperture, on through the lens and to the film.

"So I set out to make one of the lenses. This principally involved making the hemisphere. I started with a sphere of radius R, given by the formula in the left-hand drawing above, where w is half the width of the film and n is the index of refraction of the glass. For a Leica the formula called for a hemisphere having a radius of approximately one quarter inch. To make the hemisphere I first formed a sphere, by the ancient Chinese method for making a quartz-crystal ball. This was described by John M. Holeman in SCIENTIFIC AMERICAN of August, 1948, pages 60 to 63. A chunk of glass is sawed, chipped and ground by hand to a subangular sphere, then ground to a perfect sphere between two rotating brass tubes charged with abrasive grains [see drawing at left]

"'The tubes should have walls from about 1/16 inch to 1/32 inch thick,' Holeman wrote, 'and have a diameter about two thirds that of the rough sphere of glass. One tube is fastened to a vertical spindle and rotated at a moderate speed by a motor. The ball is placed on top of this tube. The other tube is of the same size and is held on top of the sphere at an angle of about 15 degrees. The sphere is charged by means of a paintbrush dipped in coarse Carborundum grains and water. The grains embed themselves in the soft brass and cut the glass on a curve. The ball rotates and is cut on all surfaces by the two tubes. This is the principle of the lens generator and of the centerless grinder. The more the ball rolls, the smoother it becomes.'

"Starting with too large a piece of glass, I had to grind it down considerably. It went nicely and became rounder and rounder. When it became too small for the half-inch tubes, I changed to 3/8-inch tubes and to finer abrasive grains. Then the sphere suddenly started to become less and less round-like the oblate earth. So I waxed a rod to one of its poles and ground on its Torrid Zone while twirling the rod, and thereafter I had little trouble. After polishing the sphere with Barnesite on felt, I ground away half of the ball to get my hemisphere and polished the flat side on felt with Barnesite.

"To mount the lens in my Leica I made the plane front element, giving it enough thickness to raise its front surface above the camera shutter-speed knob, otherwise the knob would have eclipsed a portion of the picture. I ground the shoulder on this front element with a lathe-made opticians' cookie cutter using wet abrasive grains [diagram at right]. The front element could have been made of two separate disks cemented together with balsam. Had I taken pains to paint the beveled outer edge of the front element black, its surface would not have been photographed as rings surrounding each picture. On the other hand, these rings, which are close-up photographs of the rough-ground bevel, serve to demonstrate dramatically that the depth of focus of the lens extends all the way from infinite distance down to only an inch away. Thus no focusing adjustment was needed on the camera. In another camera, where the knob is not in the way, the front element could consist merely of a thin glass disk.

"I then made an aluminum mount to screw the lens into the Leica. The first films showed that the lateral color aberration was blurring the edges, so I added a filter. For panchromatic film a yellow-orange filter probably is best, with an exposure time of one half-second in bright sunlight. With Kodachrome and no filter, the exposure time should be two seconds. The camera can be held steady enough in the hand, because a wide-angle lens has more tolerance of shake, just as the tolerance decreases for narrow-angle telephoto lenses and for telescopes.

"My 'fish-eye' lens is simple and easy to make, and has been a lot of fun to use."

One of the Sinton photographs is a fish-eye view of the world, including the entire dome of the sky. Sinton appears on one side of the picture and an automobile on the opposite horizon. Sinton's face is almost undistorted, because it is not too close to the lens.

After conceiving and making his hemispherical lens, Sinton discovered that the idea was proposed in The Philosophical Magazine in 1922 by W. N. Bond of University College in Reading, England, for photographing cloud formations and lightning flashes. "So I have done nothing new," he says. But there is no evidence in The Philosophical Magazine that Bond did more than propose the lens, while Sinton has made several.

Detailed instructions for making such a lens will be published next month.

SEVERAL months ago Edwin Hausle, a business executive and amateur botanist of New York City, dropped into our office for advice on the purchase of a microscope.

"I am making a study of plant parasites, particularly the effects of radioactivity on aphids," he explained, "and I need a good microscope. How much power do you think I can buy for, say, $100. Is it safe to pick up something on the secondhand market?"

Judging by our mail, many amateurs have the same problem. Some, like Hausle, want the microscope for a specific research project. Others are toying with the idea of adopting microscope as a full-scale avocation.

We decided to put their problem up to Julian D. Corrington, professor of zoology at the University of Miami, whose book, Working With the Microscope, has become the amateur microscopist's standard reference text. Here are his views:

"Amateur microscopy has long flourished as a hobby in both England and America, though the emphasis has been quite different on the two sides of the Atlantic. The British have the collector's attitude: they go in for diatoms pond life and. objects for polarized light Here the interest is at once more scientific, more practical and less naturalistic. Gadgets are always more or less in the foreground and the stress in subjects is distinctly toward the medical. U. S. amateurs like, in order of preference, bacteriology, histology and botany.

"Concerning the instrument, no one should make the mistake of thinking that for amateur work one needs only an 'amateur microscope,' which usually means a toy or something that should be called a miniature microscope. A serious amateur demands as good an instrument as his professional brother. Amateurs in this field carry with pride the shining banner of Anton van Leeuwenhoek, the greatest of all amateur scientists. They are, however, at a serious disadvantage compared with a modern professional microscopist: they must pay for their own instruments. A professional, whose institution foots the bills, has at his disposal more instruments than any save the wealthiest of amateurs can afford.

"We may dismiss the toy microscopes and give only passing mention to beginner's microscopes, though I have worked with a miniature Japanese instrument which is very good indeed. Unless you have only a limited or temporary interest in microscopy, you will want a full-sized, standard instrument sooner or later.

"Nothing is gained by paying for more microscope than you can use. If a beginner's model satisfies your every need, then settle for that one; if not, consider next the standard laboratory model. This is the familiar monocular, monobjective instrument, generally called a biological microscope because it is used mainly in biology courses. It can actually deal with a tremendous variety of objects, in such diverse fields as botany, zoology, histology, crime detection and industrial work The simplest type has a double nosepiece with 'low' and 'high' objectives and two eyepieces, likewise low and high.

"The next advance is the so-called medical microscope, which is equipped with a triple nosepiece, an oil-immersion objective, a substage condenser and a mechanical stage. The oil-immersion objective permits higher resolution and magnification, and the mechanical stage enables the operator to cover a field of view completely and systematically and to make measurements. With this instrument an investigator may study bacteria, cells, nerve tissue, chromosomes and many other subjects requiring high power and precision. Only a photomicrographer or a highly trained specialist needs any better equipment. A binocular body for two-eyed vision is a convenient luxury with this instrument.

"Of the more advanced types one is the wide-field binocular, actually named the binocular-binobjective microscope. It consists of two separate microscopes arranged side by side, like binocular field glasses. Since it doubles the number of lenses and prisms needed, a buyer is prepared for the sad news that its price is also considerably higher. Its magnification is low, running from twofold to 20-fold, and it is used for relatively large objects. Its great advantage is true stereoscopic vision, and it is unexcelled for work with animal embryos, insects and the small forms of life in general, including parasites, plants and dissected organs, such as bones, teeth, plant parts, the brain and spinal cord and the like. It is also much used for examining coins, stamps, fingerprints, ballistics, textiles, paper and other industrial subjects.

"People who work primarily in the field of crystals, notably rock and mineral structure, use a petrographic microscope with accessories for applying polarized light. There are also many other specialized types: e.g., the centrifuge microscope, the slit-ultramicroscope for observation of fine particles, the comparison microscope, the dark-field, ultraviolet, monochromatic, phase-contrast and electron microscopes.

"This bewildering array need not confuse the amateur-in-search-of-a-microscope, for in 99 cases out of 100 he will want either the biological, medical or wide-field binocular instrument. In selecting the type to be bought, the first question is: What is the microscope to be used for? If one wants to study bacteria, nothing less than the medical microscope will serve. It is no good buying a lesser instrument and then hoping that gadgets or stains will supply the deficiency. If a medical instrument is out of your reach, you had better change your hobby or postpone the purchase until you have saved enough money.

"Whether you should buy a new instrument or a secondhand one is in some respects like the question whether you should buy a new or used automobile: it may be partly a matter of taste. But there is little in a microscope to wear out or deteriorate, and an older model, though perhaps not quite as smart looking as the latest, may be every bit as good in performance. Unless the microscope has been abused by generations of students or has been dropped, it should be as good as new for all practicable purposes for many years. Doctors often sell instruments in excellent condition after they no longer have use for them; most young doctors today have no time for work with the microscope and seldom keep their instruments after graduation. If an older model has had good care and can be obtained cheaply, it is a good buy. The metal parts may be brass instead of chrome and the fine adjustment will probably be vertical instead of horizontal, but such things have no bearing on the performance.

"If opportunity permits, submit the secondhand microscope you are considering to a qualified judge. Sometimes this may be a teacher of biology, but not all biologists know much about microscopes. An optician is likely to be more expert. If you must rely on your own examination, begin by inspecting the objectives. Unscrew and remove each one in turn, remove the eyepiece and look at the front lens of the objective through the eyepiece, holding the latter inverted. With good oblique lighting this should disclose any scratches. Any considerable amount of pitting or scratching should be cause for rejection. But the lens may simply be stained or soiled; wash it with soap and warm water, or clean it with alcohol or xylene (used sparingly).

"The cost of eyepieces is so small that if one is scratched or chipped it can readily be replaced. After the objectives, the most important part is the fine adjustment, which is expensive to repair. It should work easily, without wobbling, backlash or lost motion. The coarse adjustment is less critical. If the tube runs up and down too stiffly, or if it is loose, the repair is trifling and the trouble of no consequence. Likewise a key can fix up an inclination joint which is too tight or too loose. Inspect the iris diaphragm for meshing of the leaves and freedom from rust. Look at the mirror, the substage condenser and its gears, the mechanical stage.

"Removal of fungus and repairs of the objectives, adjustments, condenser and diaphragm require factory-trained personnel. You may send the parts or entire instrument back to the factory to be rebuilt or repaired. Most of the larger cities now have one or more repair men, former employees of the major optical companies. They may safely be entrusted with your job if universities in your area use them. The total cost of a secondhand instrument, including repairs and replacement parts, should not go over two thirds that of a new microscope of the corresponding model. If the model is out of production, even though its parts are in excellent condition the price should not be more than one half that of the corresponding new model.

"The rules for care of a microscope are simple. Handle it gently, remembering that it is a precision instrument. Keep it covered when it is not in use; dust is a microscope's greatest enemy. Wipe dust away with a soft, lint-free linen handkerchief or piece of chamois. Use a camel's hair brush on the lenses, mirror, gears and diaphragm. To clean glass surfaces, use a handkerchief or lens paper, moistening it with the tip of the tongue. Do not touch these surfaces directly with the fingers, for that is bound to leave oily fingerprints on them. Do not oil the microscope. Once every five or ten years, depending on the amount of use, have an expert repairman clean and adjust the whole instrument.

"Neither price nor power should be the deciding factor in your selection of a microscope. The most expensive or the most powerful instrument is not necessarily the 'best' for your purpose.

"I shall answer briefly a few of the common questions about microscopes.

"What is the limit of their power? In an optical microscope the limit of resolution is an object the size of one half a wavelength of light. An electron microscope can distinguish much smaller objects because the wavelengths of electron beams are much shorter than those of visible light.

"Why is the laboratory instrument called a compound microscope? Because the image is compounded: the objective first forms a magnified real image of the object, and the top lens of the eyepiece then magnifies this real image further and makes a virtual image. The latter cannot be magnified, because it exists only in the mind of the observer. To increase magnification of the real image by projecting it a greater distance is no help, because it does not improve resolution, that is, show more detail.

"What is resolution? If you project a silhouette of your hand on a blank wall by means of a light, you show no structural details of the skin. This is magnification without resolution. Resolution is the capacity of a lens to show two close objects as two, rather than as a single fuzzy one. Diatom shells, which often have exceedingly fine lines of pores very close together, are favorite test objects.

"Why does a high-powered lens cost so much? Because they must be built to correct certain inherent defects of lenses. One is spherical aberration: the failure of all the rays of light to meet in exactly the same focal plane. The peripheral rays are refracted more sharply than the ones passing through the center of the lens. The other serious defect is chromatic aberration; this results from the fact that a lens refracts the shorter wavelengths of light more sharply than the longer ones. The image is therefore fogged by a halo of separated colors. To correct these defects requires the grinding of lenses of different composition, such as crown glass and flint glass, and the cementing of these elements into a compound lens. The higher the magnification required, the more complex the problem of correction. This calls for numerous very small elements, carefully ground and assembled with the greatest degree of precision. Lenses that have been corrected to a degree satisfactory for visual work are termed achromatic. Those corrected still further are called apochromatic; they are over-corrected and require compensating eyepieces. They are used only for advanced research in special fields or for photomicrography.

"Can you be cheated in buying a microscope? Yes, you may be if your instrument is obtained from a dealer who has no reputation to sustain. Never buy a microscope in a pawnshop unless you are granted full opportunity to test it thoroughly. A new microscope made by any major optical company is always trustworthy; each instrument is thoroughly inspected before it leaves the factory.

"Which make of microscope should you buy? I am asked this question more often than all the others combined, and the answer is: It is entirely a matter of personal preference. The question is silly-like asking whether you should buy Chevvy or a Ford. You can't go wrong on any of the major makes."

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.