Training The Retoucher

The incompetence of a large proportion of retouches is a, fact which many photographers know too well. Thin deplorable state of things is chiefly doe, I consider, to the sloppy methods of instructing that are in vogue in the profession. Much valuable tins U waited in having to inspect the work of such assistants before it goes to the next department, whereas it ought to be expected of them to be competent enough to pass it along through all departments until final inspection. I advocate the giving of an abort allotted time and direct personal attention for a few days as a bogs tune-saver in the long run, and as an aid to high quality.
The majority of assistants do not know what retouching exactly should be. Generally speaking their knowledge does not go beyond the idea that they must aim at a decent stipple. What should be done, or -what to do for the greatest improved effect with the least possible amount of labour, and how it affects the next department ('i.e., the enlarging and "finishing" artist) they lack knowledge of. In some cases masters lack knowledge of art principles and their application. Retouching taught without these, in my opinion, is absolutely valueless. Supposing the method usually adopted in training pupil for retouching was applied in the darkroom or printing-room, disaster would sooner or later happen to a batch of work or soon tell its tale by the work not proving permanent. Naturally the first thing one does in these rooms is to explain the reasons for doing certain things.
Some sort of guidance in theory ought to be in vogue among all photographers who have the profession at heart beyond that of the mere making of money. The pupil wants a thorough knowledge of what is required in the branch he is being instructed in. One would not look at the end of a pencil to draw a straight line; otherwise there would be no means to the end in getting that line straight. The mind judges where that line should be to be straight and the brain directs the hand accordingly. It cannot be said that the hand directs the pencil to make the line straight; if the pencil is held correctly the mind draws the straight line. I take this principle as illustrative of my method of instruction for retouching. A negative cannot be retouched unless the whole affect required is in one's mind. How to hold the pencil is half the battle. I have noticed that retouches who hold their pencils at right angles to the negatives and the forefinger tightly in the shape of triangle are usually bad workers and their stipple is wormlike and has no symmetry. This is caused by their being unable in this manner to work the fingers freely, the guidance having to be done by the arm and wrist, making the arm an eccentric.
The correct style, and one which saves hours of labour for the finishing artist, is to hold the pencil very loosely between the thumb and first two fingers, and almost perpendicular, thug using; the side of the pencil point and obtaining any desired angle of movement above the wrist by the fingers (the little finger resting on the negative). Never mind how you get a stipple so long as you work to follow the lines of the muscles of face and texture of the skin of the sitter, not to smother the negative. Many so-called expert retouches (stipples) place a beautiful sheen of lead all over the face, whether it is old man, lady, or child; in reality, a lead wash, such as a painter employs as a ground-tint. It is an absolute waste of time, and the effect mechanical, causing many a master to employ two retouches where one would suffice, and giving an effect which is artistically and commercially valueless. Aim at altering defects only and improving the artistic value by the following course: Select your pupil and give half an hour's persona' instruction each day for a week, first getting the pupil to master the taking away of complexion blotches and spots. Aim at nothing else until the pupil can do these to match the surrounding ground without overlapping.
The next step is to instruct where the muscles are exaggerated by the necessary side-lighting of the studio. With a satisfactory stroke there should be no so-called stipple. Then get your pupil to look at the whole of the face and imagine the negative as a line drawing in the positive sense, considering exactly what lines would be drawn to represent the character of the person (dismiss the half-tones for the moment). Get the pupil into the habit of bearing in mind the curve of the main lines that represent the character, such as the shape of the nose, main lines of lips and eyes. Any small complementary shadows there are to these do not need retouching. The next to consider is the relation of the strong highlights to the imaginary line drawing, and in doing this treat all the half-tone lights as that of a thin wash of paint an artist would put over his drawing. They need no altering; only blending into the main lines (i.e., massed shadows). The direct alteration of any half-tone or massed shadow representing the line of the facial muscle is fatal in retouching. These are the chief points to consider for artistic retouching. Any other work such as squaring noses and altering nose shadows are not necessary, if the face is properly lighted. All that is needed is the minimum work and the maximum result, which is only obtained by keeping the whole face in mind all the time. Try this method on your next pupil as against the old style of practice-practice without aim and you will be surprised at the result and time saved.

GEO. F. BURRELL.

The Longevity Of Photographic Prints In Relation To Record And Survey Work.

A recent dictum of the Camera Club indirectly revives the question of the permanence of different printing processes to be used as records by photographic survey and record societies. Perhaps the most widely understood meaning of the word "permanent," applied to everyday things, appertains to inalterability, but in photographic circles when questions arise as to tine relative permanence of different printing processes their respective "durability" is generally meant and as so understood. Degrees of (.inalterability is rather a contradiction in terms, whilst durability may widely vary. To put the matter bluntly, if any printing process will afford lasting results for, say, a dozen, or so years and upwards, it is generally considered to be permanent in the restricted sense alluded to. But the matter is on another footing when, photographs are to serve as records for posterity, for here it is not enough that they should last for fifty or even a hundred years, but a life is reasonably demanded limited only by the holding together of the picture supports. By general consensus of opinion, two commercial printing processes only, or variants of them, fulfill this condition. The life of silver prints at the best is one of conjecture, which the lapse of time only can settle, and many are known to be more or less evanescent. In the case of photographs utilized purely as records their useful existence is longer than for most other purposes: if discolored or partially faded, so long as all details are preserved, they serve their purpose. On the other hand, when once deterioration has begun it often proceeds apace.
Though all are agreed that complete fixation and thorough washing are essential elements in the stability of silver prints, yet it cannot be said that deterioration can only be ascribed to these operations being ecamped, and there may be operative causes which are quite unsuspected. Printers of the old albumenized paper have narrated how prints known to be hurriedly fixed and washed have sometimes long outlasted those which had received orthodox treatment. In past days albumenized prints appear to have been over-washed, as in addition to prolonged changes by hand they were frequently left to soak all night. Impure air, damp, impurities in the mount or mountant, or a mountant tending to turn acid or are all known factors tending to alteration and fading Even with one brand of paper puzzling differences he durability of prints arise, one worker recording rapid fading, or other troubles, whilst another experiences he opposite. Inquiries often fail to reveal any variation in procedure to account for such difference, which in some irrational way seems to be connected with the ''personal equation" which looms largely in other directions.
In daylight silver-printing processes the image may be to consist of something in the nature of a stain, whilst with bromide prints we have reduced silver in a fine state of division in gelatine, and the general opinion is that them are the most stable of all silver prints. The life of a dry-plate bears on the permanency of bromide prints, though we should expect the former to outlast the latter owing to the silver and gelatine being present in greater degree, and also to the fact that there is no paper to retain residual traces of hypo. Comparatively few old dry-plate negatives show unimpaired condition, but at Greenwich Royal Observatory there is no indication of fading in any dry-plate negatives of stars, although many date back more than twenty years. Doubtless scrupulous care was exercised in fixing and washing and none have been indemnified or even reduced.
Whilst nobody can place a limit on the life of a carefully made bromide print, which may last many a long year, yet the official pronouncement of the Camera Club that "a well-made, thoroughly fixed and washed bromide print is probably as permanent as a print in any other process" cannot be justified. The probabilities are against this conclusion, and at variance with the opinion of recognized authorities, and with the views of the great majority of photographers. In essence, the assertion is equivalent to saying that finely divided silver, vulnerable to many adverse influences, is as stable a substance as, say, lamp- black, or platinum black, both regarded as unalterable trader every atmospheric condition, and respectively employed in the carbon and platinum processes. Having regard to the support and to the fact that the platinum image is in actual contact with the fibred of the paper, mercenarily of the highest grade, a platinum print may present an advantage over % carbon when a long-distant future is concerned, but both can fairly be bracketed together as truly permanent photographic printing images. Neither, of course, exists commercially on the strength of feature, but on the distinctive qualities associated with them. The extraordinary resisting properties of platino- type prints were illustrated some yean ago, when a number remained at the bottom of the sea for some months in a sunken warship and were eventually salved none the worse for the adventure. Subsequently shown at the Brussels
Exhibition, they perished by fire. Although the image of a carbon print is not in contact with the fibred of the paper, the pigment it locked in insoluble gelatine, known to be most durable in Ha normal state, and presumably more so when tanned by the action of light. As to the danger of peeling, sometimes alleged to exist, all that can be is that this is of the rarest occurrence, and when it does take place may usually be traced to the under-soaking of the transfer paper, or over-hardening of the prints by chrome alum or similar chemical, or to undue baste in drying Preference, naturally, will be given to those tissues which contain carbon pigment, however durable other pigments utilized may be.
If the opinion of those responsible for the recent utterance of the Camera Club is based on the undoubted fact that many bromide prints made years ago show not the slightest signs of alteration, this proves that the prints are long-lived, but affords no information as to their ultimate life. We have in our possession a framed salver print (apparently albumen) of French origin purchased over sixty years ago, made long prior to the introduction of bromide papers, and only during the last few years has it shown signs of deterioration, though continuously exposed to daylight, and occasionally hung on walls none too dry. Possibly in another twenty years or less the picture may have disappeared.
Granted that carbons and platinotypes are the processes for record work, which nearly all secretaries of photographic record societies fully recognize, yet the unfortunate fact remains that if these were insisted upon few prints would be received, as the majority of amateurs print in neither process. So such societies are practically forced to accept silver prints, and with no guarantee even that they have been thoroughly fixed and washed. Possibly a dry silver print hermetically sealed and kept in the dark might last almost indefinitely, but this is outside the region of practicability. However stored for access, it is impossible to prevent a limited circulation of air and of any impurities in it over the prints owing to barometrical changes. Dry-mounting on pure paper, and a coat of good varnish applied to the surface, should materially help towards longevity. In the case of subjects obviously valuable as records, the loan of the negatives might be sought to enable permanent prints to be obtained, but unfortunately funds are often not available for the purpose. We feel sure carbon or platino type printing concerns would charge on the lowest possible basis, and on inquiry have received from two well-known firms an unofficial intimation to this effect.
There appears to be no specific authority conferred on any local authority to enable a small grant to be made for such a worthy object. But when the record society becomes part of the public free libraries (as in most cases should be the case for convenient reference) the general powers of expenditure are available. These are by no means great under the existing rate, which leaves but little margin for the purchase of necessary books, to say nothing of other desirable acquisitions. Many towns, however, have proposed an advance in the rate to 3d, and if than materializes prospects will be brighter for the societies associated with the libraries, if not for the ratepayer.
We wish all good-luck to the scheme of the Camera Club, and commend our observations to its attention, and in doing so a gentle reminder may be given to readers every where not to forget their local survey and record in the approaching season. Upon the executive, as a rule, falls the major part of the work, cheerfully undertaken and with no hope of being personally thanked by posterity, but we would urge a large measure of contribution by the general body of photographers.

A Bichromate-Mercury Iintersifier

It was while working under active service conditions that the experiments leading to the discovery of a new method of intensifying negatives .was made. Some very brilliant results were required in the way of transparencies, and the only plates in tock of the size wanted were very stale, and though labelled "Process," would not give even ordinary printing density. So the only thing to do was to make the best possible, and then clear and intensify as much as possible. Lead was tried, but owing to the lack of proper washing accommodation, bad water, and also to the strong colour it gives to the very slightest trace of veil in the whites, it did not answer in this case. After trying every method that I could to persuade the "quarter-bloke" in charge of the stores to let me have the material without the usual circumlocution, and still not getting enough density, I began to experiment, and eventually found a method of greatly increasing the density without risk of stain provided that the negative was thoroughly fixed.
The procedure finally adopted was to bleach the negative in an acidified solution of potass bichromate (as for chromium intensification), and then, after washing for a short while, immersing in a mercury-iodide solution, and after a further wash to darken the bleached image in a sulphide bath; or else in a hydroquinone developer if there were any likelihood of subsequent reducing being called for.
I found that a lot of washing, after fixing the plate, between the various baths, was not essential to clean working, and the increase in density was far greater than I have been able to get with any other intensifier except lead. If the bichromate is not all out before the negative goes into the mercury bath, it comes out into that solution, but does not seem to affect its working.
Like the mercury-ammonia intensifier (which it easily beats for density-giving power) this new method can be worked with out accurately weighed and measured solutions, but in that case it requires rather a lot of bottles. Being minus reference books or any accurate measures at the time referred to, I got on quite well without, and did not find any appreciable difference resulting from varying strengths and proportions of ingredients of solutions. The way I arranged matters was, first of all, to keep a saturated solution of potass bichromate, of which a little was diluted for use as required, and a few drops of hydrochloric acid added. If this did not bleach it was poured into a jar, and a few more drops of acid poured in. This bleaching bath does not keep, so it was thrown away after use. The mercury-iodide bath, on the other hand, keeps well in the dark-room, and can be used over and over again. As I had no formula by me, I made a fairly strong solution of each of mercury bichloride and potass iodide. Then a little of the latter was put aside, and into the remainder I poured the mercury solution a little at a time, well stirring and shaking to dissolve the red precipitate that forms when these two chemicals are mixed. A point is reached when a little of the red powder fails to re-dissolve, and it was to get this into solution that the email quantity of the potass iodide liquor was kept aside. On adding this to the bulk the precipitate disappeared. This strong solution was kept for stock, and was used diluted, but both the stock and working solutions appeared to keep well. The sulphide solution was made as required from the crystal, but there is no reason why a stock solution should not also be employed for this. The used liquor should not be kept after the same day, as in the case of bromide toning. It seemed difficult to get the image thoroughly sulphide right through, so that if the density was too great some reduction was obtained by simply immersing the negative in a hypo bath. Another use al point with this intensifier, as in some others, is that if the plate before sulphiding is seen to be too dense or the lines are veiled, a dip in hypo solution will clear it. Of course, this means another good wash before sulphiding, and it should be pointed out that these extreme methods of working are seldom suitable for anything but line work, as the uneven nesses of the emulsion are usually very much accentuated by employing strong measures.

D. CHARLES.

EX CATHEDRA: Liver Toning; Rapid Plates and Donalty; Carbon Printing and Fumes; Simper Paratus; For Print-Out Papers.

Liver Toning.

There seems to be in some quarters a difficulty in getting satisfactory tones on bromide prints with the ordinary sulphide toning process. Instead of obtaining good rich sepia tones a rusty colour is got, due sometimes to a want of density in the negatives, or to over-exposure followed by insufficient development, while in other cases no modification in working will give the desired colour. To those who find themselves troubled in this way we recommend a trial of liver of sulphur (potassa sulphurata) as a toning agent. This has the advantage of giving a variety of colour, ranging from a warm black to sepia, including some very fine purple browns. One of its good points is an absence of the slight reducing tendency of the ferri cyanide bleacher, and another is that even if the prints are inclined to be weak there is no liability to give a "ginger" colour. The process is a simple one; the toning bath consists only of sixty grains of "liver" to a pint of warm water, a few drops of ammonia being added when solution is complete. This should be raised to a temperature of about 100 deg. Fahr, and the print immersed until the desired colour is reached. A little allowance must be made for the further toning action, which goes on in the subsequent washing. Borne papers will stand the heat of the solution without requiring hardening, but if there is any tendency to melt the prints should receive a preliminary bath of formalin, a convenient strength being two ounces to the pint. As with the hypo-alum bath, all papers will not tone to sepia in the liver of sulphur solution, some is refusing to go beyond a purple black similar to P.O. P. A few trials with various papers will show the most suitable makes.

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Rapid Plates and Donalty.

It is commonly believed that it is difficult to obtain full density when using very
rapid plates and some operators prefer to use a slower grade in order to secure plucky negatives. The idea is fostered by the fact that the films of nearly all fast plates appear much more transparent before development than do those of slower ones, and this gives rise to the belief that such plates are thinly coated and lacking in silver. Such is certainly not the case; the fast plates having in some cases twice as much silver bromide spread over the square inch u the "ordinary" ones. We have used plates which were so transparent that ordinary printing could easily be read through the emulsion, but which gave almost perfect opacity when developed. The fact is that much longer development is necessary for a fast emulsion than for a slow one. If we take two plates of the san e make, one an ordinary and the other a "supersensitive" expose both correctly and develop in the same developer for the same length of lime, the difference will be most marked, but if the rapid plate be developed twice or even three times a long the densities will then be pretty even. Instead of prolonging the development the Mine effect may be produced by increasing the amount of alkali, or by raising the temperature of the developer. With regard to the former expedient, a little mishap which recently occurred to us will be instructive. By mistake carbonate of soda was used instead of sulphite in making a stock pyro solution, and by so doing the amount of alkali in the mixed developer was more than doubled. Upon developing for the usual time plates which normally gave thin delicate images became so dense that considerable reduction was necessary before the negatives were printable, a conclusive proof that a full quantity of silver was present.

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Carbon Printing and Fumes

In some unaccountable way the notion, has been created that carbon tissue is extremely sensitive to various fumes, and many have been deterred "from using this charming process because they thought that special precautions had to be taken to avoid "tinting," or what would be called "fog" in other processes. We have recently seen excellent carbon prints, which were produced day after day under conditions which are popularly believed to be impossible. They were made in a work-room in which an evil-smelling dry mounting press was used almost constantly; by the side of the sink a geyser was used to supply the hot water needed, and three feet away the sulphide of bromide prints was constantly done. The reason for the immunity from the ill effects of this combination was a simple one; only ready-sensitized tissue was used. In a dry state the fumes had practically no effect upon it, and the short time it was exposed while wet during the mounting did not allow any action either. The great stumbling-block in carbon work is the drying when home-sensitized tissue is used, and practically all risk of "tint" may be avoided by drying the tissue in an air-tight box or cupboard over chloride of calcium. By so doing, not only is the atmosphere excluded, but the drying is done in the same time whatever the hygroscopic conditions may be outside. Another advantage gained by this method of drying is that the tissue is of uniform sensitiveness, which is not the case when it is dried in the open.

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Simper Paratus

There is an old joke which is sometimes trotted out when anything uncommon presents itself "that you always see these things when you have not got your gun." If for gun we substitute camera we are recording the experience of nearly every photographer. Most of us can recall many occasions when we have seen effects of light and shade, or occurrences, which are not likely to be repeated, and have been compelled to leave them unrecorded because our camera was out of reach. We have known some photographers, mostly enthusiastic amateurs, who never went out without a camera, and at least one professional who did the same, told us that, on the whole, the practice had been a profitable one, besides being the means of securing many pictures of personal interest. This was in the days when the smallest camera was of the dimensions of a cigar box, and it required much more enthusiasm than in these times of pocket Kodak’s and "baby" plate cameras. Apart from the constant carrying of a camera, it is an excellent to keep a small instrument, say, half-plate or less, ready filled with plates or films which can be picked up and used without a moment's delay. In this respect the amateur with his film outfit is usually much better prepared than his professional brother, who often has to assemble his outfit before it is ready for use. Perhaps the most convenient apparatus is of the folding local plane or "press" type, in which plates can be kept for weeks without danger of deterioration. Such a camera is of great value for sports, pictures, street scenes, and the like, while used with discretion it is very handy for home portraiture. The great point is that it should be semper paratus, always prepared.

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For Print-Out Papers.

The consistent reader of the photographic papers is constantly coming upon hints so ancient that, like the anecdotes of Miss Volumnia Deadlock, they have become in the cycles of time new again. At least forty years ago photographers who had need to make a very dense part of a negative impress its detail fully on the print would use for the purpose the concentrated light of a burning-glass. This old expedient must have been disinterred scores of times or, quite possibly, has been invented by those who have heralded it as a new device. Its latest appearance as something original is in a recent issue of a New York photographic paper. None the less, it is a plan which may often be employed with advantage in the case of negatives of interior subjects in which most probably windows or other brightly lighted parts have become too dense in the developer. In place- of risking the negative by reducing or rubbing down the more opaque parts, an ordinary reading-glass of about three inches diameter may be held in front of the negative during printing and, while kept gently in motion, caused to concentrate its light upon the part which needs help. The American writer prefers to fit a disc of black card with a hole in it in the rim of the glass and so to obtain the utmost concentration of light.

Assistants' Notes: Dark-Room Clock

How to Construct a Dark-Room Clock.

A clock to measure the seconds, the face and fingers of which be plainly seen in the dark room, is a most desirable and useful ring. But one specially made for the purpose at the present time is rather an expensive item. The following instruction will enable any photographer to adapt an ordinary clock at vary little cost. Any make or sue will do providing it has a good, bold, white dial and a minute finger, and is one without a which will go in any position like a watch. Unless it has a finger it will be of no use for our purpose. It does not how old the movement is or bow defective it’s time-keeping qualities; these are of no consequence. If we have not one in our one can be picked up very cheaply, often for a few at a clock repairer's or secondhand stores.
Having secured this, we can proceed with the work of converting into a dark-room clock.

Carefully take the movement out of the case, noticing particularly bow it m fixed in, and remove the fingers. Sometimes this latter has to be done before the movement will come out of the case. All screws, washers, fingers, ate, should be put into a purser or small tray so that they will not get lost, as they will be required later. We should now carefully look at the works and notice just those wheels and spindles which are required to keep the clock going and the minute finger moving. All the rest of the movements are not required by us, and are better taken out. The beet way to take these out without disturbing any other works is to cot through the spindles which carry the wheels with a three-cornered file anywhere where it is convenient. They can then easily be taken out. When all the unnecessary parts have been removed we shall have a clock which, when going, only takes round the minute band. The dial should now be pot back on the clock in such a manner that the centre of the dial where the hour hand was should be fixed over the minute finger movement. This may necessitate a little cutting of the dial, etc., or other parts, to allow it to fit in its right position, but can easily be accomplished. When this is fitted in position the long; finger is carefully soldered on to the minute finger and blacked, the minute finger placed in position, and the whole movement put back into the case. We have now a clock which takes just one minute for the finger to go completely round the dial, and each of the hours five seconds. The dial being of a large size and white, and the finger black, it is very easy to see and count the time in the dark room. Of course, the clock will go with once winding as long as ever it did.

The British Achievement In Aeroplane Cameras.

The progress made during the war in the design and manufacture of cameras for photographing from aero planes has hitherto remained undisclosed except by the few and somewhat sensational statements which were published now and again in the lay Press, and which, it may be said, were usually wide of the mark. Misers, Brock and Holat, in the paper which we reprinted in our issue of February 21 last, made certain sweeping claims to priority which in the following issue provoked denial n the part f two correspondents, both exceptionally well-informed as to what has actually been done in the production of cameras for the British air forces. Since the appearance it paper we hare had an opportunity of inspecting at the Kid Brooke camp of the Royal Air Force cameras representing the whole range of instruments which have bean used daring the war from the earliest days until its termination. The paper by Major Charles W. Gamble at the Optical Society on March 13 last has also set forth in try great detail the steps by which aero plane photography has been raised to great stats of perfection. It is therefore well that tone account be given of what has been accomplished and of the stages through which the aerial camera has passed.
At the outbreak of war photographs bum aero planes or airships had been taken only in quite a casual and amateur way, and the military authorities were low to recognize the great service which aerial photographs would reader to the Intelligence Branch of the Army. Within a law months, however, the value of the aerial photographs received recognition, and cameras specially made for the purpose were first need early in 1915. The first or A model, long since abandoned, was of a quite primitive type, consisting of wooden square-section cone-shaped body, carrying a lens of eight or tea inches local length and fitted with a Mackenzie- Wisbart adapter for envelopes taking 5x4 plates- The camera had to be held in the hand and pointed vertically or obliquely downwards by the observer as he stood up in the aero plane. The Mackenzie-Wisbart system allowed of a considerable supply of plates being taken up, but the relative fragility of the envelopes in the circumstances of their being handled by a wearer of thick gloves, coupled with a want of sufficient precision in bringing the plate accurately into the local plane of an f/4.6 lens, caused this form f plate-holder to be abandoned.
Early in 1916 a modified pattern, the C model, of the first instrument was put in the hands of airmen. It differed chiefly from the previous model in the means adopted for holding and changing the plates. The camera was fitted with two magazines, one containing eighteen 6x4 plates, in metal heaths, which was placed immediately over the local plane, and the ether (empty) magazine below it and to one side, the camera, of course, pointing downwards. By means of a horizontally moving metal plate, the lowermost of the plates awaiting exposure was pushed to one side and was received in the lower magazine, the operation of thus changing the plate also reciting the local-plane shutter under cover of the moving metal plate. The principle of mechanically changing plates by discharging from a holder placed mouth downwards into one placed mouth upwards has been retained in later models in which the changing mechanism it self has been further improved.
The two foregoing cameras mere both of wood, the disadvantage of which, as pointed out by Major Gamble in his paper, was the liability to expand or contract under the very wide range of temperature and climatic conditions to which the cameras are exposed. Inasmuch as a very slight alteration of the distance between an f/4.5 lens and the sensitive surface may disturb the definition, recourse was had to cameras of all-metal construction or to one consisting of wood framework, constructed so as to obviate expansion and covered with metal mounted thereon so as to cause no stresses in the structure in the event of its expansion. The E camera of the R.F.C.; introduced in 1917 was an all-metal camera of this type, and was fitted with a changing mechanism similar to that of the C model, but with the difference that the plate was changed by pulling a cord, and, the occulting metal plats being thus dispensed with, the camera included a capping shutter to cover the aperture in the local-plane blind during re-setting. A further new device first introduced in this model was an adjustable lens cone by which lenses of from 8 to 10(1/2) inches focal length could be fitted and readily brought into use.
Up to this point all the cameras employing plates were operated, as regards changing the plate, entirely by hand, a system which had considerable disadvantages. Simple as an ordinary photographer would regard the operation of the changing mechanism, the fact that it had to be placed in the hands of men entirely unfamiliar with photographic apparatus called for a changing device which would be free from mishandling by the human operator. It need hardly be said that the airman has many other things to do besides taking photographs, and that he carries on his work always under the conditions of fire from enemy anti-aircraft batteries and of attack from enemy machines. Thus the next step and one which brought the aero plane plate camera almost to its most perfected form, was to provide a mechanical means of changing, operated by power other than that of the airman and brought automatically into operation immediately alter an exposure had been made. This was done in the L camera first used by the K-F.C. early in 1917. With it the operator had simply to use Bowden release in order to make an exposure: the rest- resetting the shutter and changing the plate was done mechanically and automatically. The ingenious device introduced for this purpose consisted of a small propeller mounted on the aero plane and connected to the camera by a flexible shaft. This provided sufficient power for the operation of the plate-changing mechanism, the changing gear coming into operation on the observer releasing the Bowden lever.
An improved model of this camera came into use in 1913 as the LB and has proved the most successful of aerial instruments. It differs from the type just mentioned in being fitted with a self-capping focal-plane shutter which can be entirely removed and replaced by another in case of derangement. Moreover it can be adjusted as regards slit-width by an external lever, and there is the further provision of operating the plate-changing by hand or power as necessary and of instantaneously altering it for use by one or the other means. A further improvement was the series of most rigidly made and finished lens cones, enabling lenses of 4, 6, 8, 10, and 20 inches focal length being used on the one camera.
The principle of a propeller drive for the mechanical changing of plates was also applied to a camera of much larger size, for 18 x 24 cm. plates, first used by the R.A.F. in 1918. The camera, which perhaps may be said not to have been quite fully perfected at the time of the Armistice, is fitted with lens cones allowing the use of objectives of from 7 to 20 inches focal length.
Other cameras of simpler type have been used both in the Royal Flying Corps and the Royal Naval Air Service for purposes more or less special to the requirements of these services. Certain of these are cameras fitted with a stout handle or grip, by which the instrument can be held and pointed obliquely in order to produce a type of photograph distinct from that obtained with a vertical direction of the lens axis. Thus in preparing for operations with tanks in France, photographs taken obliquely are necessary in order to yield an idea of the nature of the ground over which the attack is to be delivered; and similar oblique pictures are taken for many purposes of the Admiralty, for example, in order to obtain records of the correctness with which the masters of ships proceeding as a convoy are carrying out their instructions as to formation.
But perhaps the camera evolved for aero plane work which would provoke the greatest admiration of a connoisseur in mechanical devices is that known as the F, and first used by the Royal Flying Corps in 1916, after having passed through its trials at Farnborough during 1915. This is a camera taking a continuous series of 5 x 4 pictures on a roll of film sufficient for 120 exposures. The mechanism is operated by a propeller to that as the aero plane travels the photographs are automatically taken at intervals corresponding with a certain number of revolutions of the propeller. Simultaneously with the exposure of each section of film a tiny record is made on each (by means of a small supplementary lens) of the reading of the height of the machine and of its compass bearings so that each negative is provided with a record of the direction of flight over the territory which is being photographed.

Panoramic Photographs And Perspective.

The notes on panoramic photographs in a recent number of the “B.J.” will no doubt have interested quite a fair proportion of readers; and in all probability many more will welcome some amplification of the subject. And as there appears to be very little literature on this fascinating phase of the photographer's art the following notes are penned with the hope they may at least help the novice, even if they fail in the more ambitions desire to stimulate the production of a scientific treatise on the principle invoked. The panoramic camera is a necessity: there can be no question of that, and although much good work can be done by joining up several ordinary photographs, there are cases where all the skill in the world will fall to make a presentable picture; and an example, of this failure occurs when we have a view including railway lines in the foreground. At each join the lines meet at an angle and as we are not accustomed to trams tracing pentagons and squares, we are offended by the view. In a panoramic picture of the same subject, the lines will appear as continuous curves; so we are not asked to imagine the impossible, and therefore the eye and sense are not offended. To the professional mind in doubt, the big group is the most important class of work to which this camera can be put and here it is clearly scores that no argument is needed. These groups of course, are arranged in an arc of a circle with the camera at the centre; and the general perspective of the recanting picture, may be likened to one taken with an ordinary camera and a very long focus lens whose axis is at right angles to the same group arranged in a straight line. Now whatever carping critics may say, the man at the end of a panoramic group will he far better pleased than if it had been a wide-angle group; for he is in the same perspective as the man in the middle and this will prove a blessing to the photographer who has to copy a single figure from a group for the purpose of enlargement, and alas! in very many cases, the only available source will be front one of those big military panoramic groups and whatever consolation father, mother or sister can get from the finished enlargement, it will be all the greater from the fact that their departed hero is delineated in tine which would not be the case in the figure were copies from near the end of a while-angle group.
The thing that is most objectionable about a panoramic view is when something that we know must necessarily be straight comes out in the photograph as a pronounced curve. There are two ways to avoid this: one is by the arrangement of the subject, as in the case of a group, or by the selection of the point of view. Now, in general a horizontal straight line, except when it radiates from the camera, appears in a panoramic photograph as a curve: and, conversely, there is a certain curve which, when in a horizontal piano with the camera at its origin, will always appear an a horizontal straight line; and if we know the nature of this curve, we shall be in a better position to order the arrangements for any particular photograph we wish to take.
Let us take a practical example:-Fig. 1 is a diagrammatic view of Ludendorff, on horseback, giving a farewell address to his troops; and perhaps adding a few words of advice and warning mi the disastrous consequences of a complication of Prussian microcephalism and Asiatic beriberi. In the ordinary panoramic parade photograph the men dwindle away towards each end of the picture, and form a strange curve that would remind a soldier more of some lamentable straggle with the theory of a trajectory than of invincible, Vandalia, martial glory and also it offends all our ideas of perspective. And besides, perhaps, Ludendorff would not like it; he might think yon were puking fan at him, and intended some sly allusion to "elastic fronts." The remedy is to get the valiant soldier to let you arrange the men; and to get this effect of straight lines vanishing to the horizon, as in Fig. 1. they will have to be arranged in the form shown in plan by

the heavy line in Fig. 2. If we are using a 12-in. lens; and decide to have the finished picture about 40 inches long, the group will have to be included in an angle of about 180 degrees; because12^=37¾ nearly, which will allow just a little margin each end. If we further decide that the nearest soldier shall be three inches high in the photograph, and the one at the remote end of the line one-quarter that being then, by the simplest arithmetic, the nearest man must be 24 feet from the camera, and the furthest one 86 feet; and, as the group is to include 180 degrees these two men and the camera will be all on the same straight line. This is shown t., scale in Fig. 2, where the position of the camera is given by o, and B and B’ are the places of the and men. The setting out of the rest of the curve is quite simple if we remember that the panoramic projection of the horizon is a straight line, and every length of a panoramic photograph represents an equal angle or number of degrees; that is to say, if three inches at the end of a Pangram represents 15 degrees, then also three inches from the middle will represent exactly the same angle, and if the line B O, joining the men's feet in Fig. 1, is to be straight, the vertical distance between it and H O must diminish by the same arithmetical amount for each equal length of the picture; and as the distances from the camera must be inversely as the height of the figures, we have the clue to every point of the curve. Now, let us calculate the distance of the curve from the origin o for every 30 degrees. As the total fall in height is to be 3-¾, and 30 is contained six times in 180, then

is the amount required; and in the table below the distances of the points are given in feet for every 30 degrees, while the heights of the image are given in eighths-of-an-inch, to avoid fractions and show better the regular decrease.

In regard to this table it may be observed that the product of the height and distance is a constant quantity. A group arranged in this way will, in the resulting Panorama, have the same general perspective as Fig. 1 though course each element of the picture will have the perspective peculiar to the lens with which it was taken.
Now if the lines AO and BO are continued they will meet outside the picture, at the vanishing point O n the horizon; and if we call the vertical distances between A and B h and the number of degree from H to O, which in this case will be 240 deg., then for every degree the height will decrease by; therefore at any angle ß. measuring from H. the bright of the figures will be: -

and the distance from the camera to the curve of this point will be: -

It will be been that is a constant quantity which we will call a; and a ­ ß is a variable angle which we will call; then, substituting and patting r for the variable radius we have: -

,

and, clad in this classic garb, readers who have dwelt in the seventh heaven of mathematical bliss will recognize in old friend, the "reciprocal spiral." To show the nature of the complete curve it is continued in the diagram at each and by broken lines, and towards the origin it approximates more and more to a circle with every revolution it makes recording to the law –

where ra is the radius at the nth crossing of the initial line and by taking a and n of suitable dimensions we can get as near as we like to any tiled circle. By making is very small the whole curve approximates to the initial line; and if we take it small enough we have the special case of the radiating straight line. This from this spiral we can get in our photograph a right line at any degree, of obliquity and perhaps enough has been said to make clear the general law: -
The panoramic projection of a reciprocal spiral in a horizontal plane with the camera its origin is a straight line and only this carve or some special phase of it is so rendered.
But in all probability it would be as difficult to get a photographer to look at a formula of this kind as it would be get Ludendorff to let you arrange his men; so perhaps a better way would be to plot the curve to several valuations, then equal lengths; and this would give a rapid approximate way of finding what one wants.
Before leaving this subject there are several practical points consider. Where shall we put Ludendorff? In Fig. 1 it will be seen that the centre-line of the picture passes through the horse's head and therefore, he must be placed so that the mid-angular line in this case the 90 deg. line passes under the head of his charger. Another point to consider is what would happen if; instead of terminating the group at B and B we continued it along towards the originals far as the curve is

marked out in the diagram by the broken line, and also at the rather end along the straight for half a mile or so; and then starting the Circuit camera at the beginning of the group, let it run round for two and a half revolutions? Still keeping to the 12-in lens, we should want a 16-ft. film for the job; but to see the sort of thing we should get, draw a long rectangle in represent the picture (Fig. 40). The group will begin three tines over and end three times, and if we draw a straight line from the bottoms left-hand end of the rectangle to the horizon at the other end to show the line upon which the complete group is standing the diagram will be completed by a line of 240 deg. and one of 180 deg from the commencement of the picture and two lines of the same lengths at the end; and as these short

lines are necessarily repetitions of parts the long one, all live will consequently be parallel to each other.
The practical outcome of all this is what every user of a panoramic camera knows: avoid such a position that gives a straight line, which in perspective ought to be parallel with the ground line; if we can get to something like 45 deg. from this position the curvature will, as a rule, be quite
negligible; all radiating lines, and also parallels to these lines if a fair distance from the camera, will be straight in the resulting panorama because, like the circle, they are special phases of our spiral.
Knowledge of the rigid conditions for a straight line will do the operator no harm and even sometimes be helpful to the practical man.
When only a moderate angle is included in included in a panoramic view, it is not beyond realms of feasibility to bring the pictorial into ordinary perspective by spying: the only conditions necessary being to bend the negative into the same curve that it had during exposure; and then project the image by means of a lens at the centre of the curve on to a flat to a line passing through the centre of the curve and the middle of the negative. This is shown in Fit 3, where we may suppose the negative was taken with a lens at 12 inches focus, and is therefore bent into a circular arc of 12 inches radius, and is being copied with a lens of 6 inches focus, which will give us a copy corrected as regards perspective, and of the same size as if the negative had been taken in the ordinary way with a 12-in. wide angle lens. Of count, the corrected copy will be longer than the panoramic view. In regard to the optical system, it is not at all necessary to have an anastigmatic; some old-fashioned thing with a field as round as a football will do better; and perhaps a thin spectacle lens with a small stop right in contact with the glass best of all. Or, of course, the lens could be rotated during exposure; but then we should lose the advantage of roundness of field. Some years ago a lady took a picture of a castle in Scotland with an Al Vista camera, held so that the lens made a vertical sweep. The towers of the castle came out like barrels, but a correct bromide print was made in the way indicated above. A special optical system would have to be devised to cover anything more than a very moderate angle, and, in many cases, true perspective over a very wide angle would prove more objectionable than panoramic projection.
In the Cirkut camera we have great advantages: we can include any angle up to 360 degrees or more; we can focus; and we have usually three different foci to choose between; but, in the matter of range of time of exposure, it is the biggest sinner of all the panoramic cameras. The quickest exposure is literally too slow for a funeral, and the longest possible time you can give is too short for a dull subject on a dull day. In cameras of the Al Vista and Panorama class, we could tackle ordinary hand-camera subjects on a bright day; and for a still subject on a dull day we could fix the camera on a steady stand and increase the exposure to anything we liked by swinging the lens to and fro as many times as necessary. And on some patterns of the Al Vista a brake, in the form of an air vane, was fitted, which not only increased the exposure, but also amused the group while it was being photographed.
In the matter of fitting new lenses to panoramic cameras this, in general, is impractical, except in the case of the Cirkut camera, where a new lens will mean also a new set of pinions and the number of teeth to the pinions will be inversely as the foci of the lenses. There will be several points to attend to in making such a substitution, which are of more practical interest to the camera maker than the photographer.
In view of a recent patent for a camera in which the image is received on the inside of a cone, it may be as well to define panoramic projection as used in the above article as the projection by straight lines from points on the object through the centre of a vertical cylinder on to the cylindrical surface itself; the intersection of these lines with this surface forming the image, which is afterwards viewed when the cylindrical surface is spread out flat to form the panoramic picture.
C. J. STOKES.