ENLARGING LANTERN (Fr., Lantern d'agrandissement ; Ger., Vergrosserungs apparat) A lantern used in enlarging by artificial light, to project a magnified image of the negative on the bromide paper. It consists of a body carry ing the illymittant, a condenser to concentrate the light on the negative and cause it to pass out from the latter in a converging cone, and a pro jecting lens or objective to receive the cone of light from the condenser and to form the enlarged image. A illustrates the optical system of the enlarging lantern, A being the illuminant, B the condenser, C the negative, n the objective, and n the projected image. The condenser must be of the enlargement ; this depends, other things being equal, entirely on the distance of the bromide paper from the projecting lens or objec tive. The objective should be capable of covering the size of negative to be enlarged, and of sufficient diameter and aperture to pass the whole of the beam of light proceeding from the condenser. The lens used in making the nega five is usually suitable for enlarging, the best possible projection lens being probably a good anastigmat. There are numerous illuminants employed for enlarging, as oil, acetylene, incan descent gas, incandescent spirit, limelight, the electric arc, the Nernst lamp, etc. Of these, limelight and the electric arc are the most efficient with regard to illumination, owing to their approximating more nearly to a small of sufficient size to illuminate the whole of the negative, or part of the image will be cut off towards the margins of the enlargement ; on the other hand, there is no advantage in having too large a condenser, but rather the reverse, as light is wasted. For a quarter-plate negative, a point of light ; but from the point of view of general convenience and utility, incandescent gas is perhaps the favourite. The proper
adjustment of the illuminant is of importance, or the enlargement will be unevenly lit. The correct procedure is to place the negative in the carrier and to focus roughly to the required size, approximately centring the light and bringing it to that distance from the condenser which seems to give the best and most even illumination. The negative is then removed, and the illuminant moved back till a dark ring appears round the disc of light on the easel. The illuminant is now carefully centred till the ring is equal all round, and is then pushed toward the condenser till the ring disappears and a perfectly even lighting is secured, the negative being finally re-inserted and sharply focused. Any after alteration in the size of the enlargement will require a fresh adjustment of the illuminant.
B shows a typical high-class enlarging lantern which has rack and pinion adjustments through out, including provision for moving the lantern body, the condenser, and the objective. The negative carrier is furnished with rising, falling, and swing movements, and a rise or fall is also permissible with the lens. C illustrates a cheaper enlarging lantern, of simple yet efficient con struction ; while D represents a useful type dispensing with the extension bellows and pro jection lens, and intended to take an ordinary camera in front. In another form of enlarging lantern, known as the ellipsoid enlarger, no con denser is used, the negative being lit by reflected light from a curved opal reflector ; these enlargers are made either for use with the worker's own camera, or with a bellows and pro jection lens, as in E, where a pair of inverted incandescent gas burners form the illuminant.