Amateur Photographer & Cinematographer (1937)

December 22nd, 1937 The AMATEUR PHOTOGRAPHER p 6 CINEMATOGRAPHER 0 as the light is moved farther back, but beyond a certain distance no further shortening is possible. The cone lengthens as the light is brought nearer to the condenser, but here again there is obviously a limit. The position of the focus of the condenser depends on the position of the lens, and the position of the lens depends on its focal length and the degree of enlargement. These positions of the lens can be worked out with suffi¬ cient accuracy beforehand, and I will repeat the method of doing it. The degree of enlargement is reckoned in “ diameters.” If a line in the negative is made twice as long in the enlarge¬ ment that is two diameters. If a 3 x 2 negative is made to give a print 12x8 that is four diameters. To the number of diameters add 1, and multiply this by the focal length of the lens, and it gives the distance from lens to paper ; divide this distance by the diameters and it gives the distance from lens to negative. Suppose we have a 4-in. lens, and we want to make enlargements from i£ to 6 diameters. 4X22=10 and io4-iJ=6| So that to enlarge 1 j times we must place the lens 6f in. from the negative and 10 in. from the paper. 4x7=28 and 28^6=4! So that to enlarge 6 times we must place the lens 4§ in. from the negative and 28 in. from the paper. When a condenser is used its diameter must be a trifle greater than the diagonal of the largest negative to be accommodated. The usual position of the negative is close to the front surface of the condenser, and its film surface is facing the lens. There is no trouble about fixing a glass negative in the carrier by means of small brass toggles turning on screws. A film negative is generally sandwiched between two pieces of glass, the rebate of the carrier being made sufficiently deep to take them. The focal length of the lens should be about the same as the diagonal of the negative, which it must be capable of covering sharply right to the corners. In other words the lens should be capable of making the negative, so that the lens from the camera with which the negative was made will probably be suitable. Unfortunately, in many modern cameras the lens cannot be removed and transferred to the enlarger. In other cameras the lens screws into a flange, and in such a case it is an easy matter to get a similar flange to attach to the front panel of the enlarger, and then the transfer of the lens is a matter of a few moments. A good alternative is to look out for a suitable lens. An anastigmat is the ideal, but a good rectilinear lens can be picked up second-hand at a very low figure. It may need stopping down to f/n or even f/16, but that is not a serious disadvantage. W. L. F. W. TVTOVELTY CALENDARS FOR XMAS AND By C. CHAFFEY. NEW YEAR GIFTS AT this time of the year quite a L number of amateur photo¬ graphers prepare photographs and attach small block calendars for use during the coming year. The process about to be described is simple, inexpensive, and will give an added value to prints so treated, in view of the fact that not only is the date available, but also an approxi¬ mate indication of the weather, 'thus rendering it in effect a photographic barometer. To the modern generation of amateur photographers the method of making these prints will probably be new. The essentials are : (1) a bromide print of a river scene or seascape with a “ blank ” sky (not smaller than half-plate) ; (2) suitable mounts for same ; (3) small calendar-blocks, and (4) an inexpensive solution, referred to later in this article. The procedure is as follows : — The enlargement is hardened for 15 minutes in a 10 per cent solution of formalin (e.g., formalin 1 oz., water 9 oz.), after thoroughly fixing, and is well washed in running water for an hour. The print is then dried, trimmed and mounted by any method familiar to the operator. The next step is to fix the calendar pad, either direct to the lower margin of the mount itself, or suspended from the lower edge of the mount with short lengths of coloured ribbon. A loop of ribbon should also be attach¬ ed to the back of the mount near the top edge, strong adhesive being used ; this is to be used for hanging the finished article from a convenient support. Next comes the conversion of print to barometer, the following formula being used : — Gelatine (Nelson’s No. 1) 120 grs. Cobalt chloride . . . . 60 grs. Glycerine (pure) . . . . 24 drops Water . . . . . . 6 oz. Prepare thus : pour into a cup (not a glass) 6 oz. of water and add the gelatine in small pieces, stand the cup in a saucepan of hot water and submit to gentle heat. When the gelatine is thoroughly dissolved add the cobalt chloride and stir till dis¬ solved, after which the 24 drops of glycerine should be added, the whole being vigorously stirred. Now, with a medium-sized artist’s water-colour brush (No. 2 or 3 will do) apply the mixture to the sky and water portions of the print and leave a few hours to dry. The parts of the print that have been treated with this solution will acquire a bright blue hue in dry weather which changes to ‘ a pink colour in damp weather, the cause of this change being due to the effect of moisture on the chloride. 708 A suitable phrase in the form of a rhyme should be neatly written on the lower margin of the mount, which could read something like this : — When the sky is red, I feign Very soon will come the rain, But whene’er it turns to blue. Sunshine is in store for you. or : — When the skies are turned to blue. Old King Sol will soon peep thro, But when it’s tinged with red you bet ’Twill very shortly turn in wet. The novelty is then complete ex¬ cept for brief “ Instructions for Use ” which should be written on the back of the mount, stating that this baro¬ meter should not be hung near a fire, but on a wall subject to the natural atmosphere prevailing. Of course, it will be realised that other subjects may be similarly treated, the dress in a lady’s portrait, flowers in a still-life subject, etc., and dis¬ cretion of the photographer must be used in this respect. The cobalt solution will solidify on cooling, but may again be rendered liquid by submission to gentle heat, when it is required for further use. Prints submitted to this treatment are not materially affected in quality if previously hardened as instructed, prints I have treated three and four years ago show no sign of deteriora¬ tion whatever. 25