CANDLE BALANCE (Fr., Balance d chandelle ; Ger., Kerzenwage) An instrument employed in photometry to ascertain the loss of weight undergone by a candle after burning a given time.
Lighting effects in a photograph, apparently due to the use of a candle as the illuminant. Actually the candle pictured plays no part whatever in the real illumination of the sub ject. This branch of work was made popular by Newson Gibson, who, during the years 1901 to 1904, produced many remarkable candle-light effects which were puzzling at the time, as it was well known that a candle did not give d sufficiently actinic light for ordinary photography. The secret consists in using a piece of lighted magnesium wire hidden from the lens, but placed as near as possible to the candle flame, so that the light from the magne sium appears to come from the candle, the back ground immediately above and behind the candle being quite black. A blackened holder supports the magnesium wire above the candle, and is invisible against the black background. Proper arrangements must be made for carrying off the smoke. In the illustration above, Auer, represents the amount of the subject taken in by the lens, the candle being placed as shown and the remainder of the picture being filled with suitable objects. The blackened shield or tube, with the wire behind it, is shown at E, and is lowered until the wire ignites, the smoke escaping up the tube and not showing in the picture.
Another arrangement B is also recommended by N. Gibson. A strip of wood G 3o in. long and in. wide is faced on the side that goes nearest the camera with black velvet ; to the top is loosely fastened a long rod n as a handle for the operator, so that the light shield itself hangs vertically, whilst its weight prevents any motion. On the reverse side of the wooden strip is fast ened a triangular chimney j made of tinplate, its bottom being about in. from the lower
end of the wooden strip. At the bottom of the chimney the magnesium ic is placed, in such a way that the wire may be easily lighted when lowered on to the candle, and the smoke may escape up the chimney and out of the picture. When the magnesium ignites, the shield is raised to expose the flame of the candle and the exposure is made. The long chimney is necessary when the candle is low down in the picture, but when near the top and the smoke has not far to travel a shorter chimney may be used. Another worker uses a platinotype tin, as shown at B, one half at the bottom being cut away and the magnesium wire F suspended from a wire running across the centre, the whole arrange ment being suspended on wire and let down on the candle. It matters little what method is adopted as long as the magnesium is hidden and burned as near as possible in the position of the flame. The flame of the candle must also be kept steady during the exposure. A little daylight may at times be used to light up the dark corners of the room, but it must not be too strong, as the light must appear to come from the candle itself. The necessary exposure can only be found by trial ; as a basis for experi ment, expose for the whole of the time during which i in. of magnesium wire is burning and after it has burnt out allow another second for the candle flame, the stop being //II and the plate extra rapid. The "lamps " described have an effective radius of only 2 ft. or 3 ft., so that subjects must be arranged accordingly.
The unit for photometric work in England. The light emitted by a standard candle. (See " Unit of Light.")