The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Flash Light
constructed the lens. Often flare is due to the edges of the diaphragm aperture being worn bright, and this no doubt is a general cause for its sudden appearance in a lens. The Iris diaphragm, but lately introduced for photographic objectives, seems to be particularly liable to this, from the friction of the tongues of metal of which it is formed ; others state that when the lenses are mounted in cells which are not blackened, a flare is almost certain to make its appearance. All lenses should be examined for this most annoying effect, which can rarely be wholly eradicated. It is very often a defect in portrait lenses when such are used for outdoor work v/here any portion of bright sky is included in the background, and in this instance it is clearly an image of the lens by reflection from the surfaces. The remedies are not by any means satisfactory, as, whatever is done, at its best the flare spot is so distributed over the whole plate instead of being localised. When the diaphragm edges are worn bright they should be blackened, and the cells in which the lenses are mounted should also be attended to. It can be eliminated partially as stated above, by altering the position of the diaphragm slightly ; but as this is used to reduce distortion to a minimum, the remedy may be worse than the disease by introducing this defect. Slightly altering the relative positions of the two lenses will often efface it, but, as said before, only by distributing it.
Flash Light. One of the most useful lighting methods for portraiture at night is to so suddenly burn magnesium or alu-minium dust that an instantaneous flash is produced, the combus-tion being so rapid that the exposure is finished before the sitter has time to move. One disadvantage of flash-light portraiture is the fact that the eyes of the sitter are generally shown as having the iris unnaturally open, and an unusual expression results. Magnesium dust, or the very finest aluminium bronze powder, may be blown through a spirit lamp or gas flame by means of a piece of a halfpenny pea-shooter, or one of the very diverse but essentially similar flash lamps sold in the shops. Three grains of magnesium will suffice for a portrait if a rapid portrait lens is used and also quick plates; but it is important to work in an apartment with a low and very white ceiling and a white sheet on the floor, to act as reflectors. Success depends largely on
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