The Dictionary Of Photography

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

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Ad                                                                          Adapt*
tight, and from which the paper can be drawn in small piece
to allow of its exposure to light and comparison with a standar
tint, which can be obtained by exposing a plate on a subject the
exposure of which is known, and at the same time exposing the
actinometer and noting the time of the darkening of the paper t
a certain tint. Supposing the correct exposure of the plate to be
3 sees., and it is found that the paper takes 30 sees, to darker
it is obvious that dividing the actinometer time by 10 will giv
the correct exposure, with a certain stop and class of picture
from which the others can be calculated. Ordinary albumenisei
paper, which owes its darkening properties to chloride of silver
is sometimes used, and, although the results, with certain modifi-
cations, are some guide, it is obviously unfair to calculate the
exposure of bromide of silver from the action of chloride. The
term Photometer (q.v.) is sometimes, but erroneously, applied to
such an instrument. Under the title of " Actinograph " Messrs
Hurter and Driffield have devised a system of cylinder and slide
rules for determining exposures in conjunction with their systen
of plate speeds. For details of this and other instruments set
Exposure.
Ad. The Latin preposition ad is often used in recipes in the sense of ''until," or "up to," to signify the making up to a pre-scribed volume or weight. Thus, after the mention of soluble ingredients, "water ad 1 pint," would mean sufficient water tc make the ultimate volume 1 pint. Making solutions, rather with the solvent up to a given volume, than by adding a given volume is obviously desirable in all dosimetric operations in which the fluid is ultimately to be measured rather than weighed, as the volume of a liquid is affected by solids dissolved in it. (See Solutions and Solubility.)
Adapter. When using two or more lenses of different sizes it is necessary either to have a separate camera front for each lens, or else, by the aid of smaller supplementary flanges, to screw the lens into the largest flange. These supplementary flanges are called adapters; the term has also been applied to a supplementary bellows, which, affixed to the back of a small camera, allows a larger plate to be used. A convenient method of extemporising an adapter is thus given in The Amateur Photographer: - "From the imprinted edge of a newspaper -
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