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.
814. The curvature of the field is eliminated within an angle of 72 degrees - i. e., that part of the image which is comprised within that angle is absolutely flat. The definition and depth are the same in all parts of the field.
816. The Dagor lens is free from internal reflections and the image produced is accordingly brilliant and free from flare.
817. The two combinations are placed in close proximity ; consequently, there is no falling off of the luminosity toward the edge, and the entire surface of the image is therefore uniformly illuminated. The compactness of the Dagor lens renders it extremely rigid and portable.
819. The Goerz Dagor (Series III.) as a Wide-Angle Lens. - The exceptionally fine correction of the Goerz Dagor lenses over their entire light circle allows us to use them with the most perfect results as wide-angle lenses up to an angle of 90 degrees. They will give critical definition over the whole image subtended by this angle, when stopped down to U. S. 16 (= f. 16) or smaller. Their considerable luminosity at full aperture facilitates focusing materially, for which reason alone this type of objective is greatly preferable to the ordinary W. A. lenses. Furthermore, the angle they include is equal to that provided by most wide-angle lenses stated to give 100 degrees or 110 degrees, and are free from distortion. Though it be true that some lenses have a light-circle of this extent, they do not utilize it on the plate, being not sufficiently corrected to make their full angle available. An actual image angle of 60 degrees to 65 degrees is usually the maximum they produce.
820. Note: - To find accurately, without tedious mathematical calculations, the angle covered on any size plate by any lens, proceed as follows: Draw one line, AB, equal to the length of the plate used, or more exactly to the length of its diagonal. On the center of AB draw a perpendicular line CD, the length of which should be equal to the equivalent focus of the lens. Then join CA and CB, and with a protractor measure, at C, the angle Ca Cb, which read-
Illustration No. 72 ing will give you exactly the angle actually subtended by the lens on the size plate used. See Illustration No. 72.
821. The Goerz-Anschiitz Folding Camera is a small, elegant hand camera, which is available both for instantaneous and time exposures (See Illustration No. 73). This camera is extremely compact and light, the 3 1/4 x 4 1/4 weighing only 27 ounces, the 4x5 model 39 ounces complete.
822. The camera is opened for use by simply pulling
Illustration No. 73 Goerz-Anschiitz Camera See Paragraph No. 821.
Illustration No. 74 the front out until the stays catch. Then the camera is as rigid as a solid box, the front remaining always perfectly parallel with the focal plane - a point of the greatest importance when lenses of large aperture are employed. The rapidity with which the camera is made ready, and its unobstrusive appearance, are two indispensable conditions for hand camera work, and in both respects the Goerz-Anschiitz Folding camera is the finest camera on the market. Especially do we recommend this camera to all photographers who make enlargements or lantern-slides. The perfect rigidity of its front board is a priceless feature, as it alone will insure that perfect plane-parellelism of lens and plate or film surface, which is indispensable for that class of work. Fitted with a Dagor or Celor lens, the image-sharpness is so great that enlargements of 10 or 12 diameters (144 times in surface) are often mistaken for originals. No other folding hand camera can boast of such rigid construction.
823. The front board is adjustable, both vertically and horizontally, to enable the operator to regulate the field of view from any given standpoint. More especially a "rise" of the front is employed in order to limit the foreground or bring any tall object (a high building, for example) upon the plate.
824. While the camera is a fixed-focus instrument of admirable definition for general use, our lenses are fitted in a special focusing mount, which, by increasing the distance between lens and plate by means of a lever, permits the focusing of objects down to a distance of six feet. This mount is supplied with a focusing scale easily read from the position of the lever; in addition to which, each camera has a removable ground-glass back with extendable focusing hood, which can be used for focusing before each exposure, whether one is using plates, film-pack or roll-films.