Amateur Photographer & Cinematographer (1934)

October 17th, 1934 I fHf AMATEUR PHOTOORAPHEB Ip 6 cinematographer o ‘Deaders' Questions ^ ANSWERED General. — All communications for the Editor should be addressed ; “ The Editor, The Amateur Photographer and Cinematographer^ Dorset House, Stamford Street, London, S.E.i,’* and in every case, without exception, must give the name and address of the writer. Contributions. — The Editor is glad to consider original, up-to-date manuscripts on photographic subjects. All contributions must be typewritten, or in very legible handwriting on one side of the paper only. Letters or communications arising out of matters already appearing in the paper are not paid for. The Editor disclaims legal responsibility for the safety of matter submitted to him, but he will endeavour to return rejected manuscripts, etc., when a stamped addressed envelope is enclosed. MSS. or prints that are not actually accompanied by a stamped wrapper or envelope can in no case be returned. Reproduction fees for prints are only paid by arrange¬ ment beforehand. The sending of a print, without any condition stated, will be taken as permission to reproduce it without fee. Enquiries and Criticism. — .A-dvice, Criticism and Information are freely given, but the following conditions should be read carefully before applying, as any communication which does not comply w'ith the rules must be ignored. (1) See “ General ” above. (2) Every question and every print for criticism must be sent separately through the post, and must be accompanied by a separate stamped addressed envelope. No exception can be made in any case to this rule, except so far as enquiries or prints from Overseas are concerned. (3) Neither enquiries nor prints for criticism must be enclosed with competition prints. (4) On the back of each print sent for criticism, in addition to the name and address of the sender, must be the title (if any), and the criticism coupon from the current issue. (5) Enquiries should be clearly written, on one side of the paper only, and should be specific and not general. Such enquiries as “ How can I take interiors ? ” or “ Can you give me some hints on outdoor portraiture ? ” are too general to be dealt with in this section. (6) All envelopes should be distinctly marked “ Query ” or “ Criticism,” as the case may be. {7) Prints are sent for advice or criticism on the distinct understanding that by so tloing per¬ mission is given for their reproduction without fee. We endeavour to deal promptlv with enquiries, but cannot undertake to answer by return of post, nor can we give precedence to any enquiry. A selection of those replies is printed each week, but all questions are answered by post. Enquiries from abroad must contain a coupon also, but it need not be from the current number, and should be cut from the latest issue to reach the enquirer. Spots on Films. What is the cause of the black spots on the enclosed films ? I have found the same spots on films developed by a professional firm. A. M. M. (Hastings.) Although we cannot say for certain we should think the trouble with your negatives is due to undissolved particles in the developer, but we are surprised to learn that anything of the sort has occurred with professionally developed films. We advise you to make up the developer according to instructions, and then to filter it before using it. Gaslight Paper for Enlarging. What is the objection to using gaslight paper instead of bromide paper for enlarging ? F. J. (Exmouth.) The speed of the emulsion of a gaslight paper is too low for' it to be suitable for the purpose. Varnish from Films. How can I prepare celluloid varnish from waste films ? A. T. (Birmingham.) Clean the gelatine from both sides with hot water, shred the celluloid, put it in a bottle, and just cover with amyl acetate. 'When the celluloid has dis¬ solved, thin down if necessary, and filter through a double thickness of muslin. It is used cold. Telephoto Lens. What is the telephoto type of lens that can be used on reflex and other cameras ? S. J. B. (London.) It is a lens so constructed that with a short camera extension it will give an image about as large as that given by an ordinary lens of the same equivalent focus, which would require about double the extension. Thus a 12-in. ordinary lens set for distance would be about 12 inches from the plate ; a 12-in. telephoto would give the same sized image at about 6 in. from the plate. Wellington Developer. Can you give me the Wellington M.Q. developer containing borax ? E. L. M. (Cambridge.) We think this is what you want : Metol . . . . . . 20 grs. Hydroquinone . . . . 20 grs. Sodium sulphite . . . . 200 grs. Borax . . . . . . 200 grs. Water (hot) . . . . 20 oz. Dissolve in the order named, and use neat at a temperature of 60° to 65° Fahr. Using Bromide Solution. How can I tell how much bromide solution to add to developers for various purposes ? J. C. B. (London.) You simply follow the instructions given with the formula for the particular developer. To do this you must make up a solution of known strength. This, is generally i oz. of potassium bromide dissolved in water to make a volume of 9 oz. I dr. Every 10 minims of this will contain one grain of bromide. Copying. I have been copying pictures, diagrams, etc., by daylight. What artificial light should I use, and where should the lamp be placed ? What expo¬ sure should I give at f/i6 on fine-grain plates ? H. G. (Nottingham.) It is rather difficult to deal briefly with yoiir question. You should use two lamps with equal power as nearly in front of the picture as you can get them without interfering with the line of sight. They should be screened so that no direct light from them reaches the lens. If you have only one lamp you should give half the exposure with it on one side and half with it on the other. It is useless to attempt to suggest exposure, as this must be found by actual experiment, and also depends on the character of the subject copied. There is some useful information on the point in the Burroughs Wellcome Diary. 364 Testing Lens. I have bought a medium-priced anastigmat, and wish to test it by copying some printed matter. Can I reasonably expect hair-line sharpness at both the centre and edges at full aperture ? E. C. M. (St. Margarets.) With a good anastigmat lens you should get satisfactory definition all over the plate at the same time. The test you name, however, is a somewhat severe one, and to get the best results it might be necessary to stop down the lens somewhat. It is largely a question of the degree of definition that you would consider satisfactory. In our experience several moderately priced anastigmats stand the test quite well. Infra-red Portrait. I have attempted to take a portrait by infra-red, strongly heating two irons and pointing them at the sitter. Five minutes gave a blank negative. Will you tell me if the exposure was adequate ? R. L. H. (London.) You are evidently unaware of the fact that to take a portrait by infra-red rays demands a very powerful light passed through an infra-red filter. We should advise you to get the necessary information on infra-red photography from Messrs. Ilford, Ltd., of Ilford, Lon¬ don, E., or to buy a textbook on the subject. Silhouettes. I wish to make some silhouette portraits by posing the sitters in front of a sheet. If a piece of magnesium ribbon is burned about five feet behind the sheet will the light be sufiicient for an exposure of one second at f/8 or f/ii ? D. J. M. (Surbiton.) You will have to find out by experi¬ ment the exposure to give for your silhouette portraits. .\11 that is re¬ quired is to be able to get sufficient density for the part of the negative representing the sheet. What exactly do you mean by “ a piece of magnesium ribbon ” ? Is it an inch, a yard, or what ? Curled Negatives. Can you tell me how to prevent film negatives from curling ? G. McD. (Manchester.) All roll films have a tendency to curl, in spite of the gelatine coating on the plain side, and, as far as we know, there is nothing that will prevent this. You do not say how you keep your negatives, but if they are put in envelopes in the usual way they will not curl unduly. Making Enlarger. I am wanting to make an enlarger ; can you let me know of any books telling me how to do this ? Will a Ross st-in. f/4.5 lens be suitable for the above ? S. E. C. (Helper.) We have frequently pointed out that we know of no books in print with instructions how to make an enlarger. You overlook the fact that there are dozens of different types, some of which are quite beyond the capacity of any amateur to make. The lens you name would probably be satisfactory for any enlarger up to quarter-plate size, but more than this we cannot say. You say nothing about the size of negatives you intend to use, nor whether the enlarger is to be horizontal or vertical, with or without condenser, nor what light you propose to employ. 24