Tuesday, June 3, 2008

Some Notes On Print-Meters

           Of the many forms of print-meters, or actinometers, the type dependent upon miniature negatives of graduated density is preferred by some, as no matching of tint is required, and for occasional work with only a few frames exposed it certainly is convenient. On the other hand, the most accurate of all probably is the "single-tint" tint-matching type, almost essential when many frames have to be kept going and taken in and out during the day's work, but it requires constant inspection, and if one tint is over-done accidentally only a rough estimate is possible to compensate for the over-printing. Single-tint meters, such as Johnson's, supplied by the Autotype Company, are provided with a roll of P.O.P., which under varying atmospheric conditions does not always make a good match: with the surrounding tint, the yellow glass above necessarily being of insufficient depth to remove colour contrast. Greater accuracy in reading is secured by not attempting to effect a colour match, but to work in the following way: If the nearest edge of the rectangular aperture is viewed obliquely from a fair distance with the eyes partially closed, it will initially stand out lighter than the darkening silver paper beyond it, and at a certain stage will merge into the tint and be lost, which point is taken as "one tint." Tests have shown that this method largely eliminates the personal equation, one printer, practically speaking, registering the same number of tints as another, whereas in the case of colour matching by gazing directly downwards on the meter wide differences in the estimation of what constitutes a tint have been found. A variant of "Johnson's" is the circular meter with disc refills: it is cheaper, but for professional use the former is the better. In some cases celluloid is used to protect the tint, but it is an indifferent substitute.
           To insure accuracy with thin or medium negatives, the meter should register three or four tints during the printing, accuracy being of more importance when printing platinotype or palladiotype by meter than with the carbon process, which has greater latitude in exposure, or, rather, errors in exposure are more readily corrected in development. But a quick-printing single-tint meter is a decided nuisance when dense negatives are being dealt with, and in such a case a fixed-out lantern plate dyed yellow with bound-on cover-glass can be placed over the meter and will be found very useful to slow down its indications. As a matter of curiosity, it may be mentioned that the extreme variation in the rate of contact printing met with in one trade printing concern ranged from three minutes to twenty hours, the negatives - being exposed to the same
Some Notes On Print-Meters Fig.1


mercury light, and each negative affording good prints. The perpetrator of the twenty-hour gem had "faithfully promised his customer a dozen prints at the end of the week," as is usual in such cases.
           Other forms of print-meters based on tint-matching are illustrated by "Sawyer's" and the "Akuret," the sensitive paper being exposed under translucent tints of different densities. They possess an advantage over the single-tint type, as no movement of the paper is required whilst the negatives are being printed, but their scope is not so wide. The familiar Wynne's meter, dependent upon numbers successively printing out, is a favourite with many, though others experience a difficulty in deciding whether any particular number hat, or has not, appeared Finally, the type first alluded to is the device of Mr. H .J Burton, on the lines of which the making of an efficient home-made article is to be described.
           Not a few have attempted to make print-meters of the graduated miniature negative order, by copying a photograph in the camera, or by exposing by contact a dry-plate behind a positive, in either case successively on different parts of the plate, with an increased time of exposure for each small negative, but this method is very uncertain, and the results are usually far from satisfactory for fairly obvious reasons. It is also obvious, when mentioned, that to attempt to design a meter capable of indicating exposures from thin negatives up to those of extreme density, either means an undesirable multiplication of the tin; guide negatives, or an equally undesirable abruptness in the translation from one to another. For unnaturally dense negatives, one or more pieces of ground-glass placed over the meter will meet the case.
           Fig. 1 represents a quarter-plate negative of nine prints stuck on white cardboard, which are reduced by copying in the camera to a little less than 2*(1/2) inches high over all, in position shown on the plate. The prints should be of the same subject, preferably a portrait rather large on the plate, and whilst it is an advantage that the set be uniformly lit, even illumination is not essential. Over-exposure is to be avoided as bright, but fast printing negatives with almost clear glass shadows are the moat suitable. If the ground prints through it is blocked out.
           Assuming the figure to represent the glass side of the plate, and the negatives to read from left to right in the usual way, the graduation in printing rate is effected by covering No. 2 with one layer of celluloid, about the thickness of that used for cut films, No. 3 with two layers, and so on. Fig. 2 shows the first sheet of celluloid applied with extremities extending beyond the miniature negatives,

Some Notes On Print-Meters Fig.2

but clear of the edges of the glass; on the right about 1*(1/3)th inch, on the other three sides more space is available. The next sheet has space 2 cut away, and is stuck down at each end with a touch of celluloid varnish, the procedure being continued mutatis mutandis until No. 9 is covered with eight thicknesses.
           When the first test of the meter is made everything may appear right, the lower numbers being nicely graded, and on printing further the faint images of the highest numbers apparently the same. But here exists an unsuspected trap, for on printing, say, No. 5, to the "pretty" stage, No. 6 may now be found to be almost indistinguishable in depth, and therefore require further ho. ding back, together with the numbers following it.
           Accordingly, the only safe plan is to test each number right through the series at its "pretty" stage against the next less printed one. Some pieces of stripped thin roll- film may be found of service when only a very slight holding back is demanded. The celluloid covering is then edged all round with cardboard slips stuck down with seccotine, and a thin cover-glass bound on. If the lower numbers print too quickly for the negatives in use, the cover-glass may be of ground-glass. A three-quarter-view quarter-plate printing-frame holds the finished article; white wood frames are sold sufficiently deep to take it. A packet of 3*(1/2) x 2*(1/2) ordinary gelatine P.O. P. provides the meter paper, and will keep for years if stored in an airtight tin with some dry calcium chloride. Self-toning papers are not so good for the purpose. When the number indicating the correct exposure is found by trial, naturally only a narrow strip of paper need be utilized afterwards.
           In the model constructed, which has worked well, for identical depths of printing the last number requires about six times the exposures of the first, a range sufficient to satisfy most requirements. This ratio, of course, only holds good for the particular thickness of celluloid employed. Comparative values might be given each negative if a single-tint meter is at hand, or improvised, by registering the number of tints necessary to bring each negative in turn to the pretty stage.

Monday, May 26, 2008

Practicus In The Studio: Studio Exposures.

            Correct exposure is one of the most important of the factors in making perfect photographs, yet the majority of portra approach it in the most casual manner, and apparently trust to a sort of sixth sense to tell them how long to keep the shutter open, or as one Mid to me, "It is like taking a dire into water; when I press the bulb, I do not know when I am coming to the surface.” With long practice it is possible to work successfully in this sab-conscious way, but most people will find it desirable to have some definite idea of the number of seconds necessary to give the exact quality of negative which is aimed at. I want you to take particular notice of those last words. There can be no fixed standard of exposure or density in portrait work, or we should all arrive at one monotonous style, without that touch of individualism which now distinguishes our best photographers from one another. Twenty or thirty years ago there was an established ideal of a clear, sparkling negative ranging from clear glass to opacity, and a high-class operator who did not conform to it had little chance of employment. Many negatives which would be appreciated to-day were then thrown aside as failures, because they were too soft or too hard to print in the limited range of media then available, but now we are more free to choose our methods, and can produce negatives to satisfy our own artistic instincts. Therefore it is necessary if we are to be consistently good in our work we must not trust to "flukes" for our successes, but to study the conditions under which our particular class of negatives can be obtained.
            On asking one of our best known outdoor photographers bow he secured such uniformly perfect negatives. I was told that they were obtained by "exposing to suit the developer.” This was in the pre-Watkins days, when no attempt had been made to systematize development and most people believed that the clever worker owed his success to modifying the developer according to the appearance of the imago, often beginning with plain pyro solution, and working up the negative by adding alkali and bromide drop by drop. This idea is now exploded, proving that my friend was a true prophet when he asserted that the prime factor in producing the negative was correct exposure Hurter and Driffield, to whom photographers owe so much, have taught us that the amount of silver affected by light when a plate is exposed is in definite proportion to the length of exposure given, bat this assumes that all the so affected is reduced by the developer, or, in other words, the plate is “developed right out," which is rarely the case in studio work, most portraitists finding that such a procedure produces too much contrast. This fact has been recognized by both plate and developer makers who prescribe different times of development for portrait, landscape and copy negative, the former always being much shorter than the latter two.
            To establish a correct method of exposure we must make a few experiments, working with a standard developer, and a fixed time of development, which may be obtained by the factorial system, the only variation being made in the exposure. It is convenient and economical, besides assuring uniformity of rapidity in the emulsion, to make several exposures on one plate, and this can easily be done in most studio cameras by fixing a small mask in the camera back and marking the slide so as to show when the plate is in position. The easiest size is to work three upon a half-plate, cutting a mask with opening two inches by four and fixing this in the existing carte or cabinet mask. If the slide has notches for single exposures, and also for repeating two C.D.V. on half-plate, the centre notch may be used, but new marks s little farther from the centre must be made for the two end exposures. For my own use I have made a repeating back which allows of four exposures, each three inches by two clear, from the rebate upon a half-plate, and this I find handy for many other purposes.
            The exposures, which must, of course, be upon the same subject, may be varied in any proportion which the operator desires. Usually double at each step will be found as good as any for portrait work, as our negative will then show us the effect of one, two, four, and eight seconds' exposure. The result will be rather surprising to those who try it for the first time; for, supposing that the one-second exposure gives a thin but printable negative, it will be found that the eight-seconds section, although thick and slow to print, will also yield a passable result. That, however, is not my point, which is that the operator should now select the exposure which gives him the quality of imam- he wants, or if none quite pleases him should give an exposure between the two which he judges to be nearest correct. So far so good. Now all depends upon correctly estimating the value of the light, and this can better be done with an exposure meter than by the exercise of personal judgment. If we use an ordinary Bee meter and note the time taken to match the tint at the. time of making our exposures we shall be able to establish a ratio between meter time and exposure for any light or lighting. For example, if we find that our selected exposure is four seconds, and that it took right minutes to get the tint, we haw the proportion of half a second for each meter minute. Naturally I do not propose that anyone should make meter tests while sitter waits, but an occasional test between whiles can easily be managed. The plate speed and lens aperture must be unchanged, or due allowance must be made, or this system will be worse than useless.
            It is often found that when strong effects of light and shade are being tried for that the negatives turn out hard and chalky and do not at all represent the model as seen by the artist. There are two causes of this, both closely connected, under-exposure and over-development, the latter being due to an attempted to force out shadow detail. Now, if development had been done by time without regard to the appearance of the image, we should have retained the detail in the high lights, but the shadow detail would still have been wanting. Longer exposure would remedy this without giving flatness, unless-unite an unreasonable time were given. This class of subject affords an excellent field for the progressive series of exposures already recommended; or if it be thought that the effect cannot be judged from so small s plate two full-sized exposures may be made, one receiving three times as long as the other, both being developed for the same time in the same dish.
            It is important when making experiments in exposure to keep not only to one make of plate, but to the same grade. Emulsions vary in character, and two grades which are, perhaps, marked 200 and 240 H and D, cannot be relied upon to give the same quality of image, even if the difference in speed be accurately allowed for; much more is this the case if two makes of plate he mixed up. For the same reason one developer should be adhered to, and for printing quality land adaptability to various subjects and lightings there is nothing to beat the old-established pyro-sods. Remember that a negative is only a means to an end, and that "pretty" negatives do not always give the best of prints. Although not strictly within my subject, I feed that at the present time of year it is not amiss to on that pyro is less affected in its action by variations of temperature than most other developing agents. I have only recently found the slow action of another developer mistaken for under exposure, with the result that the exposures were increased and flatness resulted.
            A point which mart not be missed is the effect of the distance between lens and sitter upon exposure. This is always allowed for in copying, but is often overlooked in portraiture. Most operators know that a large head requires more exposure than a full length, other things being equal, but perhaps could not toll you why. There are two reasons, one being the increase in the focal length of the lens a the sitter approaches the camera, and the other the flattening of the lighting by the greater amount of atmosphere which intervenes as the sitter is placed further from the camera. Let us consider the former case, assuming that a head measures 9 inches in height and we are making a 3 in. image of it: this adds one-third to the camera extension, supposing we are using an 18 in. lens working at F/6 for infinity; one-third added to the focal length gives us 24 ins - in other words, we are working at F/8, which requires practically double the exposure. When taking a full-length cabinet the reduction would be l/12th, which would only add an inch and a half to the original focal length, and this we could safely ignore so far as exposure is concerned. In the second case the increase in exposure is only apparent, not real. If there is a certain amount of fog over the shadows it covers the bare glass, but there is no more detail in the shadows than there would be if the atmosphere were perfectly clear. In London, where the atmosphere is as thick in winter as it is in most places, many photographers use a lens of shorter focal length than they would otherwise, in order to avoid this flattening.
            In conclusion, let me impress upon the notice that correct exposure is the key to satisfactory results. Leaving colour effects out of the question, any arrangement of light and shade can be correctly reproduced if the proper exposure be given. We can flatten the scale by over-exposure, we can sharpen it by under-exposure, so that if we hit the happy mean we shall get upon our negative what we saw when looking at the sitter. Surely such a consummation is worth taking pains to attain, instead of following the usual "hit or miss" way.


PRACTICUS.

A NEW YELLOW DYE AND LIGHT-FILTERS MADE FROM IT.

           In the early days of orthochromatic photography the dye generally used for the preparation of light filters was picric acid, this having the advantage of simplicity and cheapness and of great efficiency, picric acid absorbing the ultra-violet almost completely, and having a wry sharp cut in the spectrum. The disadvantage of picric acid, however, is that it is unstable to light, filters made with it soon turning brown. For this reason the early gelatine filters were made chiefly with tartrazine, which is very stable and gives permanent niters. Tartrazine, however, has the disadvantage that its absorption in the ultra-violet is unsatisfactory, and even moderately deep tertrazine filters transmit appreciable amounts of ultra-violet, this detracting very much from their efficiency. For this reason filter yellow, introduced by Hoechst in 1907, rapidly displaced tartrazine as the best dye for filter-making, and has held that position ever since.
           Filter yellow is extremely stable, absorbs the ultra-violet strongly with the exception of a transmission band at 300μμ, which, since it is absorbed by glass, is of little importance, and hat a satisfactorily sharp out for the preparation of orthochromatic filters. A disadvantage of filter yellow which has always been recognized, however, is the fact that its absorption curve was less sharp than that of picric acid, and for many purposes, especially the preparation of very light filters, a dye possessing the stability and ultra-violet absorption of filter K, but of greater sharpness of cut, would be desirable.
           When the need for light-filters of high efficiency for aerial photography arose the need for such a dye became pressing, and we undertook a search for such a material. After a great number of trials it was found that suitable absorption and stability were possessed by the phenyl-glucosazones.
           When certain sugars, such as glucose, are warmed with a solution of phenyl-hydrazine in dilute acetic acid, yellow precipitates are produced possessing definite crystalline structures, by which the sugars may be characterized. These yellow substances are known as osazones, those formed with phenyl-hydrazine being termed phonylosazones. On measurement of the absorption spectrum of glucose-phenylosazone it was found that the absorption curve was very sharp and extended far into the ultra-violet, and since the material is well known to be stable, it appeared that a dye prepared from it would possess the properties required for the preparation of light yellow filters.
           Glucose-phenylosazone is insoluble in water, so that to obtain a dye it is necessary to have a salt-forming group present in the molecule, and to produce a dye suitable for use with gelatine it was desirable that this group should be an acid one. To obtain such a derivative of glucose-phenylosazone which will form salts with metals it is merely necessary to substitute for phenyl-hydrazine a derivative containing an acid group and condense glucose with it in the same manner. Several such derivatives were tried, and the most satisfactory result was obtained with glucose-phenyl-osazone-para-carboxylic acid. This was prepared in the following way:-
           Para-nitrotoluene was oxidized to give para-nitrobenzoic acid. This was then reduced to para-aminobenzoic acid, which was diazotized, and gave para-hydrazino-benzoic acid or phenyl-hydrazrne-para-carboxylie acid. The glucosazone of this acid is a yellow crystalline compound insoluble in water and almost insoluble in alcohol. It forms a sodium salt which is extremely soluble in water, but which can be precipitated from concentrated solutions by the addition of alcohol, and this sodium salt of glucose-phenyl-osazone-para-carboxylic acid has been adopted by us for the preparation of light-filters under the name of "Eastman Yellow."

Fig.1

In Fig. 1 are shown the absorption spectra of tartrazine, filter yellow, and Eastman yellow, from which it will be seen that the Eastman yellow has a sharper cut than filter yellow, and almost as strong an absorption in the ultra-violet.
           Light-filters prepared from it retain these characteristics, and these light-filters have been prepared and specified under the names of EK 1 and EK 2 light-filters. A special filter for aerial photography has been adopted by the American forces under the name of Aero No. 1.

Fig.2

Fig. 2 shows the absorption curves of these light-filters.
           As regards stability, it was found on test that the new dye was not quite so stable to light as filter yellow, but was superior to all other yellow dyes tried, and its stability is amply sufficient for the preparation of light-filters, since it requires weeks of exposure to direct sunlight to produce a change even in the lighter-coloured filters.

C. E. K. MEES.
H. T. CLARKE.

Sunday, May 25, 2008

DARK-SLIDES OUT OF REGISTER

DARK-SLIDES OUT OF REGISTER.

           In three out of four studios that I have visited in the course of the last year or so, I found the dark slides of the camera in general use out of register with the focusing screen. The present use of rapid plates enables the photographer to use diaphragms to an extent that disguises considerably the want of fine definition, resulting from the plate not being truly in focus. In the days of wet collodion, when, in order to secure a portrait free from the unsharpness, due to movement of the sitter, it was the custom to use the lens at full aperture or nearly so, photographers had to be, and were, careful to see that their dark-slides were truly in register with the focusing screen.
           Although the want of sharpness in the negative, due to the slides not being in true register is less conspicuous when using the smaller apertures to which the use of rapid plates has accustomed us, it is still very desirable that the coincidence of position of the plate and the focusing screen should be as complete as possible, if only for the power obtained to get properly exposed results with the shortest exposures, particularly in the case of portraits of children. A photographer, the proprietor of a high-class establishment, doing a large business, writes me that since the correction of his slides his operator generally takes portraits of children with the open lens with excellent results, and with fewer failures and continent economy of time and plates.
           The plan which I employ to ascertain the truth, or want of it, of the registry of the slides, is to take a strip of wood about 3/5 or ½ an inch in thickness, rather longer than the width of the slide, and to drive a screw through it. The strip is laid across the front of the frame of the focusing screen, and the screw advanced until the point just touches the screen itself. A plate is now put in the dark-slide, the back is buttoned down, and the shutter is drawn. The strip is then laid across the front of the slide, and if it is in true register, the screw point will just touch the plate. It is desirable to repeat this trial with the plate placed both vertically and horizontally, and with each carrier that may be in use with the slide. A waste negative ix better than a plain glass for the purpose, as a paint scratch on the will indicate very closely coincidence of the two surfaces.

           The reason for having the wood a little longer than the width of the slide is (as I have found in one or two cases) that the top or bottom or one of the sides may be higher or lower than the opposite and the extra length of the wood allows the screw to be tried on different paris of the plate. The (crew is inserted at the place where it will come over the middle of the screen when one of the ends of the wood is just at the outer edge of the frame. This arrangement allows full use to l made of the extra length of wood for the testing the truth of adjustment away from the centre of the screen. The extent of deviation from coincidence is ascertained by placing slips of card of different thicknesses between the point of the screw and the focusing screen, or the plate as the case may be, until piece is found of a thickness that just fills the space.
           If it is the focusing screen that is found to be nearer to the front than the plate, a cardboard matt is rut of the same size outside as the ground glass; about a quarter of an inch wide all round except at the corners, where it is rounded inside for strength. A photographer generally has a stock of old mounts of various thicknesses, but if there is not one of just the thickness required, one or more thicknesses of cartridge paper may be pasted on to a thinner card, and when dry used for the purpose. The card matt is dropped into the frame, and the glass replaced and the slip-beading pinned in gain.
           If it ia the plate that is too near the front, slips of card are glued on all round to the rabbet of the dark-slide. It may be that some of the carriers may require adjustment independent of what has been done to the dark-slides. In this case they may be trued by gluing slips of card along the edges or the front, or, if the error is in the other direction, by reducing the thickness of the wood in the same place.
Of course, a neater job may be made by sending the slide and frame of the focusing screen to a camera maker or to an intelligent cabinet maker, if (which is not often the case) the camera can be put out of use for the time, but the home cure method described has answered perfectly well.

W. E. DEBENHAM.

Tuesday, May 20, 2008

EX CATHEDRA: Ghost Images or Flare, Camera Copies and The Shop Window.

Ghost Images or Flare

It is a known fact that many of the finest pre-war anastigmats frequently give both ghost images and flare when dealing with subjects which throw a strong light into their glasses. The defect is much lees often met when single lenses or the single components of convertible auastigtmats or R.R. instruments are employed. "Ghost images" or "flare'' are regarded by many photographers as being the more likely with instruments having many glass-to-air surfaces, and as a matter of fact, though not as a general rule, the more of these surfaces there are in the instrument the more likely is the defect to be in evidence in certain classes of work. It is not realized as well as it might lie by those who possess anastigmats which exhibit flare or ghost images that much may be done to assist in eliminating these if the instrument is provided with a sufficiently deep hood. We have in our own possession an anastigmat with no less than ten glass-to-air surfaces, and invariably when this lens is used against the light or under like conditions the defects are sure to manifest themselves, yet when the front glass is shaded with a deep and efficient hood we have never had the least reason for complaint. The rarity of ghost images or flare when R.R. or single lenses are used may be traced in part to the fact that with the former class the hoods are much more efficient: as regards the latter, when the single components of the convertible anastigmat are employed it is nearly always the front lens that is removed, and thus the mount of the lens serves as a highly efficient hood for the back glass.

Camera Copies.

The recent installation of the Photostat Patent Office brings forward the subject of quick and cheap copying of documents, printed matter, or drawings, by means of the camera. As most of our readers are aware in this and similar apparatus, the print is made by exposing bromide paper in a special camera which is scaled to various sizes. The image is normally a negative one, although positives may be made by recopying them same size. Taken in an ordinary camera the images would be laterally inverted, but this can be obviated by fitting a reversing prism or mirror to the lens, the latter being, of course, much the cheaper arrangement. We think that photographers who work for engineering and other manufacturing firms would do well to take this class of work into consideration, as it would secure many orders for copies of drawings, plans, etc., not amenable to duplication by the usual heliographic methods, which call for a translucent original. It should not be difficult to arrange an attachment to any ordinary large camera for moderate-sized subjects, while larger ones could be managed by taking a small negative and enlarging in the usual way. We have seen some excellent copies up to three feet across made in this way and as the work practically mechanical, highly-skilled labour is not necessary. On point is essential, and that is that the same lens should be used both for making the negative and the enlargement. The operation has been very successfully carried out thus: supposing an architect's drawing has to be reproduced, a copy is made upon a process-plate, say, half-plate or whole-plate size, the distances between lens and original and lens and plate being accurately measured. The lens is then transferred to the enlarger, and the negative and bromide paper carefully placed at exactly the same distances, the result being a full-sized copy free from any distortion, the image having been made to travel back through the same optical system by which it was produced. Where much work has to be done it would be well to have both camera and enlarger rigidly set to the required points so that for full-sized reproductions no setting would be necessary. With a proper artificial lighting scheme the exposures of both plate and enlargement would be a fixed quantity, and a spoiled sheet almost unknown.

The Shop Window.

A few days ago we were asked whether it was advisable to retain a shop window for the display of specimens or to be satisfied with show-cases in a lobby and let off the shop. This is not quite such a simple question to answer as it appears at first sight, since many factors have to be taken into consideration. The first of these is the class of business which is intended to be done. The highest class of portraitists depends almost entirely upon introductions and to a lesser degree upon reproductions of their pictures in the press. Some go no farther than a brass door-plate to advertise their locale, a few even dispense with this, while others have modest show-cases with only one or two specimens on view at a tine. A few of the older firms have large lobby shows or shop windows, but it is not until we reach those who cater mainly for chance trade that we find the window show really popular. Recently there has been a great increase in these window shows in London and other large centres, so that we must conclude that they have been found to be a paying proposition. It may be noted that many of the large portrait shops are being run by people who are also engaged in other branches of industry, and they have treated photographs in the same way as they would clothes, jewelers, or tobacco. Surely, therefore, it is quite in order for the photographer, pure and simple, to take a leaf from the business man's book and to go in for bold advertisement, providing that he has the means to do it properly, and not to lose sight of the next important factor in the matter that of locality. To be effective a window display must be situated where there is a considerable amount of traffic, and in what may be called a shopping or market thoroughfare, where there are other attractions. Even in the same street one position is valuable and another almost worthless. In nearly every important thoroughfare there is one side which is much better for business than the other, and this keen business man is careful to ascertain before he invests his money.

Photography's War Work

[The immense part played by aerial photography in the prosecution of the war is naturally realized by photographers, a very large number of whom have been practically engaged in carrying it on. But perhaps the magnitude of the scale is not a matter of common knowledge, and therefore we embrace the opportunity of reprinting from the "Daily Telegraph" of Monday last an article which presumably embodies official figures. It is interesting to find that in the essential matters of cameras and lenses the British forces were better equipped than the German. The fact has recently been the subject of remark as regards lenses, and the writer of the 2 notes printed below describes, it will be noticed, the same superiority in respect to cameras. Eds. "B. J."]

           When hostilities broke out in 1914 aerial photography was still in its primitive and experimental stage. A considerable amount of pioneer work had been done both from balloons and aero planes; a small but valuable literature was arising; but the impetus of war was required, with the aid of the immense scientific and technical resources behind the Royal Air Force, to exploit its possibilities. Some idea of the progress made can be gained from the fact that on the Western front alone during the last ten months of war no tower than 264,605 Royal Air Force negatives were taken in the air over German territory, and the gigantic total of 5,800,000 prints was made from these negatives for the use of the Intelligence Staff.
           The most recent types of Royal Air Force cameras are very highly finished pieces of work. .The lens itself is shielded in a deep tube which faces vertically downwards, thus preventing direct sunlight falling upon it. At the other end of the camera is a steel chamber, containing the automatic device for changing the plates after each exposure. The entire apparatus is securely fastened to the side of the machine, and u connected by a wire with the observer's seat. The pressure of a lever is sufficient to expose a plate and to bring a new plate into position. The German cameras, as recently exhibited in the Strand, lack many of the exquisite mechanical refinements of the British instrument, particularly the ingenious device by which the plates are automatically changed in the air, without any attention whatever from the pilot. This striking British invention ha enabled many excellent and valuable photographs to be taken while the machine itself has been under heavy fire both from the air and the ground.

High-Speed Photography.

           Anyone who has tried to take a snapshot from the carriage window of an express train realizes the difficulty experienced in obtaining a negative entirely free from movement. The same difficulties are, of coarse, experienced in taking photographs from the air. A modern aero plane is really a traveling observation platform moving at from fifty to a hundred miles an hour. As the pace of the machine cannot be altered, the object to be taken must be "snapped" as it slips swiftly by beneath the machine. Aerial photography is, therefore, high-speed photography of a special kind. An aerial photograph is almost always under-exposed, and this calls for exceptional treatment when the plates come to be developed. Apart from this peculiarity, however, it is the definite policy of the Royal Air Force to specialize in very thin negatives. A dense negative takes far too long to print by artificial light. A thin negative enables prints to be made in about three seconds. In this way a trained Royal Air Force photographer can print and develop as many as eighty separate enlargements in the course of an hour.
           For this scientific work the Royal Air Force has trained large numbers of highly skilled workers. In the model dark-rooms at the Central School of Aerial Photography every candidate for acceptance as a R.A.F. photographer must first pass a severe test, designed to reveal his suitability or otherwise for the work. He is then given a month's practical intensive training, particular attention being paid to the processes of development, and to the enlargement of negatives by artificial light. Much importance is attached to the rapidity with which these enlargements ran be produced, for the fate of a battle may depend upon the promptness with which large scale copies of a vital subject can be supplied to the Intelligence Staff. After a further course at a training centre in England, the airman-photographer would proceed to a service squadron overseas and be assigned to a photographic section working with a recon naissance Bight. Such a "section" usually consists of a technical non-commissioned officer and about seven men, who take in torus the more confined and laborious aspects of the work. One man will “load” the magazines with unexposed plates, another will fix the cameras to the machines prior to flight, and receive them on return; others are detailed for developing, washing, drying, and plotting the negatives. Several men are constantly engaged in tin enlarging room, exposing and developing as many as 100 prints in an hour.

Before an Offensive.

           It is during the strenuous days preceding a big offensive that photographic activity raises to its maximum. During the successive big drives made by the British in France during the summer and autumn of last year, the entire field of operations was photographed over and over again. If a new series of enemy trenches were constructed during the night, a R.A.F. reconnaissance squadron would bring home photographic evidence of the fact on the following morning. It was no uncommon thing for as many as 11,000 negatives to be made on the Western front alone during a single week preceding an important advance.
           In addition to this vast work of aerial reconnaissance, photography was also extensively used for verifying the results of artillery fire, and for recording the precise effects of bombs dropped from the sir. The very Inking photographs of Frankfort, Mannheim, Mets, Sablon, etc., recently published in the Press, were actually taken during the raids upon those towns. Another valuable development was the application of the stereoscope to war intelligence. By taking two photographs of the same object, say an enemy trench system, at an interval of a few seconds, a striking stereoscopic effect is obtained which throws all the ramparts and other elevated portions of the enemy work into high relief. In this way the principal difficulties to be encountered by the attacking party can be foreseen.
           Aerial photography is destined to become one of the big new industries of the future. The topographical surveys of to-morrow will be photographic surveys; the school and commercial atlases will be photographic atlases. Exploration, commerce, scientific research must all benefit by an industry which may well grow to very largo proportions. In this field of post-war industrial activity, Britain will inevitably take a foremost place, for she already has at her command in Royal Air Force personnel some of the most highly trained specialist photographers in the world.

Practicus In The Studio: Backgrounds

           The modern photographer regards the background of a picture in a very different light from his predecessor of twenty, or even ten, years ago. Then it was the custom to use elaborately painted scenes, which were supposed to be more or lees suited to the social standing of the sitter. Usually they were highly incongruous, and we often found such combinations as a butcher-boy in a tropical conservatory or a lady in evening dress waiting by the banks of bonnie Loch Lomond. I well remember one enterprising firm who went so far as to have the entrance to Hyde Park accurately reproduced with real posts and rails for church parade sitters, and an interior of one of the salons in Buckingham Palace for court dresses. This sort of thing was borrowed from a certain school of portrait painters who considered it necessary to depict their models in what they considered an appropriate entourage. Fortunately we have changed all that, and the scenic background is rarely used except in the "while-you-wait" studio, where it serves to cover up finger-prints and stress markings in other words, it has almost entirely "retired into the background." The painter had one reason for introducing scenic effects into his pictures which does not apply to photography, for his subject being fully coloured often called for a foil, a warm-toned curtain, or sometimes even a conflagration, as in some naval or military portraits being used to modify a rubicund complexion, while a delicate sky or light foliage served to enhance the charms of a blonde beauty.
           The modern photographer has evidently taken a lesson from stage lighting, in which a concentrated light is often thrown upon the principal character, while the garish colours of the scenery are allowed to remain in semi-obscurity; and this has been all to the good as far as the artistic nature of the result is concerned. Many photographers now confine themselves to plain backgrounds. It is a safe course, although one sometime, (eels that a little relief would often be acceptable, especially for half and full length poses. Hence a dark cloud or suggestion of foliage is often useful, as it allows the figure to show more relief by opposing a light portion to the shadow side of the sitter. There is one disadvantage in using this class of background because it is not always possible to bring the light patch into the desired position. This was overcome by a device, little known in this country, which consisted in having the background made in an endless belt running over two rollers, something like a roller towel, by which the height of any portion of the surface can be adjusted to a nicety. Such a background may carry foliage suggestions, clouds, and plain surfaces in various sections, as the length of 16 ft. affords ample room. Another device for securing gradation was to have the ground made in the form of a shallow saucer, which gave a perfectly natural effect of light and shade just where it was wanted. Such a construction was found in practice to be too unwieldy for general use, and a more convenient way of carrying out the same idea is to have a tall screen made of narrow strips of wood glued to an ordinary plain canvas background of a medium grey tint. This can be placed so as to form a kind of alcove behind the sitter, more or less concavity being given as harder or softer gradation is required, or even be used flat, while when done with it can be rolled up and put in a corner. To make the method of construction quite clear, I will compare it to the roller shutter of a studio dark slide, the wooden slips being, of coarse, turned away from the sitter. Tapestries and curtains form effective backgrounds if judiciously used, but neither the pattern nor the folds should be pronounced in character, only enough being shown to break up the flatness of a plain surface.
           The illumination of the background has an important effect upon its depth of colour, and much may be done by turning it to or from the light, while the distance it is placed under the drawn blinds gives somewhat similar modification. Thus, to obtain the darkest effect from any given tint of grey, we keep it well back from the sitter and bring the edge nearest the side light as far forward as may be, the reverse being done when a lighter tone is required.
           In the case of white backgrounds for "sketch" work it is usually recommended to light these independently by opening the blinds behind the sitter. This is all right in a dull light, but on a bright day the flood of light so projected into the lens is very likely to cause a general fog over the negative. Certainly if the quality of the work is to be considered it is better to secure opacity by Mr. Adamson's method of using red ink and seccotine on the back of the negative. A common error is to paint sketch backgrounds a bluish-white, the idea being that a denser deposit will be obtained. This is quite wrong ; nothing can be whiter than white; the blue only masks any yellow tint in the distemper, and there is no gain by adding it.
           From time to time attempts hare been made to print in backgrounds from film negatives interposed between the portrait negative or to put in backgrounds on the back of the glass. These plans are rarely satisfactory, though in some cases excellent results have been obtained. As a rule, however, the general effect is not so good as from a background which has been photographed with the sitter.
           The materials used for backgrounds are various. For plain tints Melton cloth is excellent when it can be obtained. Failing this, distemper on canvas or stout sheeting is very suitable. For graduated backgrounds distemper may also be used, but it requires a considerable degree of skill to apply it, so that the necessary softness is obtained, and for this class I therefore prefer flatted oil-colour, which does not alter in depth upon drying, and which can be easily worked and softened while wet. Aerograph work upon a plain grey distemper foundation answers very well, but it takes some time to cover so large a space. The aerograph is also excellent for subduing contrast in scenic backgrounds which are too contrasty. I have also improved such by rubbing on black chalk powder exactly in the same way as in finishing an enlargement, but care must be taken to avoid patchiness if there are decided brush marks on the surface. For small grounds up to 54 in. wide dark green or red serge is very good, and a little light may be introduced by dusting powdered French chalk on where required. This is easily removed with a clothes-brush if the plain surface is again required. If you wish to distemper your own backgrounds it is better to purchase one of the many ready-made distempers or to use the Kalko powders (Vanguard Co.). which are specially prepared for this work. Oil-colours should not be purchased ready mixed; they should be procured "ground in oil" in a stiff paste, and this should be thinned down with turpentine or on of the current "turpentine substitutes."
           Lincrusta and Anaglypta are useful for making imitation panelled backgrounds. The latter, being a kind of embossed papier mache, is the cheaper, but will not stand knocking it so well as the Lincrusta does.
           Now that we do not require so many backgrounds the old-fashioned multiple stand should be discarded and the material should be stretched upon light wooden frames fixed upon feet with castors, so that they may be moved about the studio easily and used at either end or diagonally, as may be desired. It is a good plan to have the ends of the studio finished so that they may be used as backgrounds. This has also the excellent fleet of preventing the space behind the movable screens being used as a receptacle for lumber. The oak paneling comes in very well for this, and if the entire end be covered a large group can be accommodated without having to eke out the ordinary-sized ground with curtains, side slips, and other make-shifts.
           As a guide to those who are attempting to make or renovate their own backgrounds for the first time, I give the following hints. Do not expect to get an even surface with one coat of distemper. You may do so but, if not, do not be discouraged, apply a second coat rather thinner in consistency. If working on new canvas or sheeting it is a good plan to give a first coat or filling of thin size, or even starch or flour-paste. Tins prevent the distemper from being sucked into the material, and makes it easier to apply. For oil colour, ordinary glue size is to be preferred. A large paint brush, about three inches across, is easier for the amateur to manage than the orthodox distemper brush, and should always be used for oil. Work quietly, and do not slop on too much colour at once. A good grey can be made by mixing a little Venetian Bed and blue with the black and white. This looks warmer, and photographs better than black and white alone. Remember that distemper dries many shades darker than it appears when wet; therefore before using your mixed colour try a patch' on brown paper and dry it before the fire: you will then know what your background will look like when dry. A very little white will turn black into a light grey. Do not buy black in a dry powder, as it is very difficult to mix; ask for black ground in water. Always strain your distemper through muslin before using, or eke you will get streaks which are caused by unmixed particles of colour which break up under the brush.
           There is a right and a wrong way of nailing a background on to its frame. The wrong way is to fasten all four corners and then to go round the sides. The right way is to drive a strong tack in the middle of the top edge, then to pull the canvas as tightly as possible and drive another tack in the middle of the bottom; then fasten the two sides in the same way. Having got a straight pull these two ways, begin driving in tacks about one and a-half inches apart towards the corners, always working from the centre. In this way any fulness is drawn out as you go on, and the background will be perfectly flat and free from wrinkles. It is a good plan to fasten a loop handle tit iron or brass at each side of the frame; this obviates the necessity of handling the edge of the wood, and keeps the background in much bettor condition. If the frame is wider than you can stretch, a loop of webbing or cord, about eighteen inches long, should be fastened to one of the handles. Holding this and one handle, you can easily move an eight-foot frame single-handed, although if good castors are fitted it may not be necessary to lift it very often.

PRACTICUS.