Apparatus and Material.

Apparatus and Material used in micro-photography have, from time to time, been greatly varied by different workers, some preferring to use the microscope in the vertical position with the camera superimposed or fitted on the eye-piece of the microscope tube; others, again, prefer that both the microscope and the camera should be arrayed horizontally. In another form the ordinary microscope is dispensed with and the objective stage and mirror are adapted to the front of the camera, together with a suitable arrangement for holding the object. Lastly, the camera is lain aside, and an operating-room rendered impervious to light, takes its place, and the image is projected and focussed upon a ground glass screen held in its place by a separate support. This method has been made practical since the introduction into microscopy by Zeiss of the projection eye-piece. It is well known that micro-photographs can be produced by employing these projection eye-pieces, as well as for screen illustrations in the lecture-room.

Fig. 172.—Swift’s Horizontal Apparatus.

With regard to the position of the microscope and camera, the horizontal affords greater stability than the vertical, and is on this account to be preferred. The simplest apparatus consists of a camera fixed upon a base board, four or five feet in length, upon which the microscope can be clamped, and which also carries the lamp and bull’s-eye lens ([Fig. 172]). This arrangement I have found economical and useful. No more elaborate arrangement is actually necessary. Sunlight is no doubt the best, but a good paraffin lamp is a handy and available illuminant.

With the former, and rapid plates, a short exposure of three or four seconds, even when high powers are used, is found sufficient; whereas, with the paraffin lamp it will vary from three to ten minutes.

Walmsley gives the following table for exposures with the lamp:—

1½-inch	objective	3 to 45	seconds.
²⁄₃-inch	"	7 to 90	"
⁴⁄₁₀-inch	"	½ to 3	minutes.
¹⁄₅-inch	"	2 to 7	"
¹⁄₁₀-inch	"	4 to 10	"

For micro-photography the following practical rules must be observed. The sub-stage condenser may be dispensed with when low powers are used, as well as the mirror, and the lamp so placed that the image of the flat of the flame appears accurately adjusted in the centre of the field of the microscope. The bull’s-eye lens is so interposed, that the image of the flame disappears, and the whole field becomes equally illuminated with high powers; the sub-stage achromatic condenser must be used, and a greater intensity of illumination is obtained by placing the lamp-flame edgeways. It is advisable to begin the practice of micro-photography with low powers, and a trial experiment should be made with some well-known object as the blow-fly’s tongue.

Dr. Crookshank is of opinion that, in the case of micro-organisms when their biological characters are studied under low powers of the microscope, photographs are preferable, because they give a more faithful representation of the object. A micro-organism, even under the highest powers of the microscope, is so minute an object, that to represent it in a drawing requires a very delicate touch, and it is only too easy to make a picture which gives an erroneous impression to those who have not seen the original. Photography enables the scientific worker to record rapid changes, and it is quite possible as the art advances we may find the film more sensitive than the human retina, and that it will bring out details in bacteria which would be otherwise unrecognised. The result, therefore, of experience is that in research laboratories it will come into more general use as a faithful and graphic method. I cannot better bring these observations to a close than by giving a quotation from Dr. Piersoll’s practical method of obtaining micro-photographs.

The three essential conditions to ensure success in micro-photography are:—(1) Satisfactory apparatus; (2) good illumination; (3) suitable preparations. With high amplifications (1,000 diameters and over), the conditions are greatly changed by the approach to the limit both of the shortness of the focus of the objective and of the length of the camera which can be advantageously used; for the first experience leads to the adoption of the ¹⁄₁₂-inch, for the second four feet is the limit, since a given high amplification, say 2,000 diameters, can be more satisfactorily and more conveniently obtained with a superior ¹⁄₁₂-inch connection with suitable optical means to increase the initial magnifying power of the objective, than with an unaided ¹⁄₂₅-inch lens, and the plate removed to a greater distance. Until quite recently the various amplifiers offered the best means of increasing the power of an objective, but the introduction of the projection-oculars of Zeiss is an accessory piece of apparatus, far superior to any older device. These projection-oculars resemble ordinary microscopical oculars or eye-pieces only in general form and name, being optically a projection-objective in connection with a collecting lens. The new oil-immersion apochromatic lenses, in combination with these projection-oculars, form undoubtedly the more efficient equipment for high-power work; it is as true for high-power photography as for microscopical observation in general, that the best results are obtained with fine and necessarily expensive, optical appliances. If for the satisfactory study of the intimate structure of a cell, or of a micro-organism, the most improved immersion lenses are necessary, it is to be expected that, for the successful photography of the same, tools at least as good are needed. Sunlight certainly affords the most satisfactory illumination whereby good micro-photographs can be obtained, as well as for recording microscopical images. That by good lamp-light fair impressions of objects under extreme magnification can be secured is encouraging, but the negatives produced by such illumination seldom, if ever, possess the characteristics of a really good sunlight negative, where the sharpest details are combined with an exquisite softness and harmony of half-tones.

If the mirror of the microscope be of good size, it will only be necessary to make an arm on which to support the removed mirror outside some southerly exposed window, since it is desirable to have a greater distance between the mirror and the stage than would be possible were the mirror attached in its usual place. Where the microscope mirror is too small to be satisfactorily used, a rectangular wood-framed looking-glass is readily mounted, with the aid of a few strips of wood, so as to turn about both axes.

The rays from the plane side of the mirror should pass through a condensing lens (of 8-10-inch focus, if possible), so placed that they are brought to a focus before reaching the plane of the object. The exact position of the condensing lens is a matter of experience; usually, however, the most favourable illumination is obtained at that point where the field is brilliantly and uniformly illuminated, just before the rays form the image source of light; the nearer the focus the less disturbance from diffraction rings. Ordinary objectives will require the employment of monochromatic light—produced either by a deep blue solution of ammonia-sulphate of copper, or by the green glass screen—since the optical and actinic foci do not usually perfectly coincide. Powers up to the ¾-inch will require no further condenser; with the ¼ or ¹⁄₆-inch objectives, the low power (1 or ¾-inch) serves with advantage as an achromatic condenser, when attached to the sub-stage. The Abbe condenser, although so important for fine microscopical investigation, is not adapted to photography unless a very wide cone of light is desired, which, for the majority of preparations, is some advantage; a low-power objective, used as a condenser, is found to be more satisfactory than the Abbe with a small diaphragm.[30]

The greatest delicacy in manipulation is necessary, as in working with a ¹⁄₁₂-inch objective a turn too much of the fine adjustment will cause the image to vanish. With fine preparations of bacteria it is not easy to trace the image, and hence the advantage of commencing with a well-marked object, as that of the fly’s tongue. The development and fixation of the image must be proceeded with as in the ordinary photographic process. In the text-books of photography full accounts of failures will be found, their causes and prevention. Numerous papers and suggestions for micro-photographic work will also be found scattered throughout the “Journal of the Royal Microscopical Society.”

The Projection Eye-piece has become an essential part of micro-photography, and it is so arranged that it may be employed with advantage with objectives of either the apochromatic or ordinary series for photographic purposes, projecting an exquisitely sharp image of the object on the plate. A diaphragm between the lenses limits the field, and a sharp image of it should appear on the screen when the eye-piece is adjusted. The adjustment may be effected by revolving the eye-piece cap in a spiral slot, so that the eye or top lens is either brought closer or removed farther away from the diaphragm, as may be required, and divisions and a reader are usually provided for registering positions. Such eye-pieces are made to fit any size microscope body.

Initial magnifying powers:—
English length of tube	10-in.	3 and 6.
Continental ""	6-in.	2 and 4.

Fig. 173.—Baker’s Pringle Vertical Micro-photographic Apparatus.

The microscope and camera ([Fig. 173]) are here seen to be part of the same instrument. The bellows of the camera have an extension varying from 6 in. to 30 in. The board on which the microscope and limelight jet are fixed is made to turn out of the line of the camera to facilitate adjusting the instrument and radiant, either limelight, electric light or paraffin lamp; when this is done the board carrying the same is turned back to a stop which brings the microscope into a central position with the focussing screen. An adjustment is supplied at the side of the camera, geared to the slow movement, for finely focussing the object upon the screen. A light-excluding connection is fitted to the front of the camera and microscope; immediately behind this, in the bellows, is an exposing shutter which is manipulated by means of a small milled head. Two focussing screens are usually supplied, one grey, and one patent plate, together with a double dark slide.

Mr. Andrew Pringle’s vertical micro-photographic apparatus is an excellent form; it consists of a heavy base and brass support, carrying a quarter-plate camera, grey and plain glass focussing screen, double dark back, camera extending to 24 inches, and turning aside as shown in Fig 173. It is light-tight in all its connections.

To secure uniform results in micro-photography, only thin preparations, which lie as nearly as possible in one plane, can be relied upon for good and perfect negatives.

Fig. 174.—Ross’s Arc Lamp.

An electric arc lamp specially designed for micro-photographic work, wherever the electric current is available, is that known as “the Ross-Hepworth projection arc lamp.” The advantage gained by this form of lamp is not only on account of the ease with which it may be employed, but also on account of its superior power and quality. It is of primary importance that the lamp employed to convert the electricity into light should be of a good and reliable pattern. It is not essential that it should be automatic in its working—many experienced micro-photographers preferring a simple hand-feed lamp to the one of a more complicated kind, being so much less difficult to keep in order. A good hand-feed microscope-lamp has the advantage of greater simplicity and portability.

The argand gas-light arranged for me many years ago for micro-photography may be employed with advantage. It is clean, and always ready for use when brought down to the table attached by a piece of india-rubber tubing. The incandescent form of burner enhances its value, since the light is thereby rendered whiter. The arrangement is shown in the diagrammatic drawing, [Fig. 175].

Over the argand burner B, is a pale-blue glass chimney, resting on a wire gauze, stage A; this secures a uniform current of air. The colour of the flame may be still more influenced by a disc of neutral tint, or other coloured glass, inserted into the circular opening at E, in a half-cylinder of metal, G, used to cut off all extraneous light; can be rotated on the stage by the ivory nob at H, a metallic reflector I, attached to the standard rod, on being brought parallel to F serves to concentrate the light and send it on to the bull’s-eye, and through it to the mirror, or directly to the photo-microscopic camera.

Fig. 175.—Table Incandescent Gas-lamp.

By removing the shield G, and bringing the shade M over the burner, it is at once converted into a useful microscopical lamp, for all ordinary purposes. The screw R clamps the lamp-flame at any height, while the support N carries a water-bath O, or a plate P, both of which will be found useful in preparing and mounting objects.

A special incandescent gas-lamp is made by Messrs. R. & J. Beck.