Photography is such a popular hobby in these days, that the enthusiast who possesses both camera and microscope, is certain, sooner or later, to wish to take permanent records of some of the beautiful objects revealed to him by the latter instrument. The production of high-power photo-micrographs, as the pictures of highly magnified objects are called, can only be carried out by those who are skilled in the use of both camera and microscope and are possessed of considerable patience. There is nothing to prevent any amateur photographer who possesses a bellows camera—box cameras cannot be used for this work—from producing excellent low-power photo-micrographs, that is to say pictures of objects less highly magnified.
It may be disappointing to learn that a microscope is not necessary for this work. The requirements are, a camera which will open out to a considerable extent and a short focus lens. Before we show how the pictures may be taken, we must be quite clear what is meant by a short focus lens. There are various ways of measuring the focus of a lens; in the case of a single lens the operation is fairly simple, but single lenses are made of one glass and most camera lenses are built up of several pieces of glass, then it is much more difficult to measure the focus quite accurately. For ordinary purposes and for our purpose, it is only necessary to know the focus in round figures and to do so we open up the camera and focus some distant object on the ground glass, then the distance in inches from the back of the lens to the ground glass will give us very nearly the correct focus, or as it is often called focal length, of our lens. Suppose we focus on a church steeple a mile away and then find that a space of five inches separates the back of our lens from the ground glass, the lens is of five inches focal length.
With a lens of such a focal length we shall require a camera with very long bellows to obtain much magnification of our object but, if our camera is one with only short bellows, we can still overcome our difficulties. If the extra expense is no object we can obtain one of the excellent Aldis lenses of only two inches focal length, especially designed for this work; if we are ingenious we can construct a device which will answer our purpose admirably and cost but a few pence. With the simple apparatus we are about to describe photo-micrographs up to ten diameters magnification can be obtained in most cameras. The term, ten diameters, may appear puzzling but really it is quite simple. Suppose we wish to make a photo-micrograph of a penny stamp and we wish it to be magnified ten diameters, we should require a large camera for the operation, but that, for the moment, is beside the point. Our penny stamp, magnified ten diameters, would be equal in area to ten horizontal rows of stamps, each row containing ten stamps or, in other words, it would occupy the same area as one hundred penny stamps.
To find the magnification possible with our camera and lens, extend the camera bellows to the full and set up a foot rule in front of the lens. Move the camera from a distance slowly towards the rule till it is sharply focussed, then carefully measure the distance between the inch lines on the focussing screen; if the lines are three inches apart we shall be able to make photo-micrographs three times the size of our object and we shall probably desire something better.
To obtain a considerably magnified picture we must have a lens of short focal length and a camera with long bellows, in fact in theory the amount of magnification is only limited by the length of the bellows, so that an extraordinarily long camera should give us a much magnified picture. We cannot lengthen our bellows without considerable expense, but we can shorten the focal length of our lens. If we obtain, at the cost of a few pence, a convex lens of short focal length, such as is used in cheap magnifiers we can easily apply it to our camera lens and it will have the effect of shortening its focus. This extra lens can either be fitted in front of our original lens by cutting two inches of cardboard, of such a size that they will just fit into the lens hood. In the centre of each piece of cardboard, cut two circles, slightly smaller in diameter than the diameter of the convex lens. Place the lens over the opening in one of the pieces of cardboard and stick the other piece upon it with glue or seccotine. When dry fix the lens in its cardboard holder in the front of the lens hood and repeat the focussing experiment with the foot rule. We shall now obtain a much greater magnification with the same length of bellows, because the additional lens has shortened the focus of our original lens. Probably our camera is fitted with a double lens and it is possible to unscrew the front portion, in this event our extra lens with its cardboard holder may be fitted inside the front lens up against the diaphragm and the front lens replaced. The result is practically the same whatever the position of the new lens, but we must be certain that it is convex, for a concave lens would increase the focal length of the whole and so reduce our magnification.
We may find that the amount of enlargement we can now obtain is sufficient for our purpose; if so we can go ahead and produce photo-micrographs of all the objects we desire. The methods of doing so differ in no way from those employed in taking ordinary photographs and as we are writing about microscopy and not photography in these pages, there is no need to go into further details. Even the experienced photographer, however, is liable to overlook one or two important details. The bugbear in all work of this kind, with low magnifications as well as high, is vibration. Not only is our object magnified but every movement is equally increased. No one should walk across the room while this work is in progress; in large towns, trams and heavy motors will ruin many a plate, in fact it is only when one takes up work of this kind that one realises that one’s house is in a perpetual quiver. Some enthusiasts work at the dead of night, others suspend their apparatus on springs and invent all kinds of ingenious devices to overcome these miniature earthquakes.
If time is no object, we have an easy means of still further increasing the magnification. To do so we cut a thin sheet of copper in such a manner that it just fits our lens tube, in front of the diaphragm. Then in the very centre of the copper disc we make a hole with a “number one” needle, the hole is about one twentieth of an inch in diameter. Replace the convex lens in its cardboard holder and screw on the front portion of the camera lens. A trial will show that we have considerably increased the magnification but decreased the amount of light admitted by the lens, therefore we shall probably require an exposure as long as an hour. How about the bugbear vibration during such a long exposure is a natural question to ask. Unless the vibration is continuous, and that is unlikely, it is less likely to cause trouble during a very long exposure than during a short one, because it operates during a small proportion of the whole time.
All kinds of objects can be depicted with the apparatus we have described. Minute shells and insects; parts of larger insects, their legs and wings for example; the feathers of birds; various rocks, crystals of all kinds; small flowers and their seeds; mosses, lichens and many kinds of fungus, in fact their number is limited only by the degree of ingenuity possessed by the photographer. Do not suppose that these low-power photo-micrographs are interesting only because of their size, the enthusiast who makes a collection will discover in his prints hidden beauty of which he had no conception when he looked at the originals. We have seen a very large number of low-power photo-micrographs, taken with very inexpensive apparatus, showing the wonderful sculpturing on the wing cases of beetles, some of them are marvels of design, yet, observed with the naked eye, many of the insects appear to be devoid of ornamentation.
The production of high-power photo-micrographs is hardly a subject that can be described in these pages; the apparatus is costly for, even if one dispenses with a specially designed micro-photographic camera, it is necessary to have a good microscope and bellows camera, for really advanced work. Messrs Swift & Sons supply an excellent fitting, with which quite satisfactory photo-micrographs may be taken. It consists of a light metal cone, the more pointed end fits over the upper portion of the microscope tube; the other end of the cone is provided with ground and plain glass focussing screens and a dark slide. When using this apparatus, it is first necessary to find and focus our object in the ordinary way, before attaching the photographic apparatus. Having secured our object exactly as we wish it to be depicted and well in the centre of the illuminated circle, we remove the eyepiece and slip the metal camera over the top of the microscope tube. If now we place the ground glass screen in position, we can see an image of our object upon it. Great attention must be paid to the lighting, it is necessary that the illumination be perfectly even, otherwise our negative will be over-exposed in some parts and under-exposed in others. When everything is in order the plain glass screen is substituted for the one of ground glass. On this we shall probably not see any image with the naked eye, but with the help of a magnifying glass we can see a much finer image than was possible on the ground glass screen. The final focussing is done at this stage and, having secured as sharp an image as possible, the focussing screen is removed and the exposure is made. Experience alone will teach the length of exposure, it depends upon the amount and nature of the light, upon the transparency of the object and also upon its colour. There is no more simple apparatus for taking moderately high-power photo-micrographs; for more advanced work the micro-telescope and the super-microscope (see Chapter XVII) used with a camera, will enable the user to obtain pictures of objects magnified as much as five thousand times.
