This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
An attachment to an ordinary camera, consisting of a minute lens which throws on a mirror the same image that will be reproduced on the sensitive plate, and this image in turn reflects the object to a ground-glass placed in a horizontal position. This enables the photographer to see exactly what will be reproduced.
A direct vision view finder consists essentially of a metal frame, either square or rectangular in shape, and a small sight. Both the frame and the sight are placed on top of the camera. The sight is placed directly above the center of the ground-glass and the frame far enough in front of the sight, so that when looking through the sight and the frame the latter will include the same amount of view as will be reproduced on the sensitive plate in the camera.
(See Lens, Landscape.)
(See Rays, Visual.)
A name that was at one time given to all sulphates, and designated " white," " blue," " green," vitriol, etc.
(See Acid Sulphuric.)
(See Shutter, Volute.)
A hard form of rubber which is not elastic. Used principally for making trays and other dishes for photographic use.
Water is one of the most valuable and useful substances to the photographer, yet this fact is not always appreciated. The greatest of care should be taken in seeing that the water is perfectly pure. Foreign substances in the water used for mixing chemical solutions are responsible for a large majority of failures or difficulties met with. Pure water is a colorless liquid entirely devoid of taste and smell, and possesses a neutral refraction. Pure water, such as mountain lakes and rivers which flow over crystalline rocks, is called soft water. Water containing more than eight or ten grains of mineral matter to the gallon is called hard water. Soft water usually contains more or less organic matter and sometimes a slight quantity of salts of potash, soda, lime and magnesia. Hard water generally contains a large quantity of carbonate of lime, as well as many other impurities. In mixing up the various solutions it is preferable to use distilled water, but such is not always easily obtainable; therefore filtered rain water will answer, or even-melted snow. It is advisable for every photographer to thoroughly test the water he is using, and thus avoid, so far as possible, any danger of waste material. The tests which follow will prove of special value.