209
4
Oo
Fig. 3. Sketch of an optical pantograph
pink colour. The compilation is pencilled on the plastic and then engraved; the result
is a negative.
Various methods are used to transfer text on to the original. One of them is to paste
the text on a transparent sheet of viniprose placed over the original. Another method
is to apply a thin layer of celluloid on the positive copy of the original and then to
paste on the required inscriptions.
Optical pantographs
Finally, a few words about the optical method which combines well with the photo-
mechanical method. It is most useful for supplementing an original compiled by the
photomechanical method. Often there is a need to transfer onto the blue print of the
original supplementary data, such as railways, land management, forest, etc. Among
cartographic projectors, one designed by the Central Research Institute of Geodesy,
Aerial Photography and Cartography deserves special mention. It has many advantages
over other designs based on the use of incandescent lamps. In the latter, the cartographic
material is heated up and is perceptibly deformed. The Soviet model uses luminescent
lamps, which produce practically no heat at all. It consists of a table, a camera with an
optical device and a lighting System (Fig. 3). The cartographic material is attached to
the glass of the adapter, and lighted with the luminescent tubes (daylight lamps)
5 and 7. From the cartographic material the rays pass to mirror 3, through lens 2, and
then to table 1. The adapter frame 4 moves horizontally along its base; in addition,
the Upper part may be adjusted for height to produce a sharp image on the table on
the required scale. The original is placed on the table for the construction of the
drawing.
The image is brought to scale by a special device connected with an electric motor
and pedals" The sharpness of the outline is automatically maintained by a template
inversor.
