We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
BRITISH KINEMATOGRAPHY
Vol. 18, No. 3
there has been a marked trend towards the examination of very small mechanisms, with the attendant difficulty of lighting very small objects efficiently and of positioning the camera with the required accuracy. In the author's laboratory use is made of special stands which enable the camera — or the object — to be positioned with ease. For fields down to the size of a matchbox, the Kamm stand5 is excellent, particularly if the camera has to be held over part of a large machine. For smaller areas either the camera or the object is mounted on the compound slide-rest of a lathe. In this way,
and the author uses two 350-watt 26-volt lamps in reflectors 8ins. diameter. When properly focused, these lamps will illuminate an area about 2ins. diameter to a brightness, on a white card, of 70,000 foot-candles. Lamps of this type generate considerable heat and concentrate it in a small area, so that precautions must be taken to avoid damage to the object under investigation.
For smaller areas still, say, 3 to 5 millimetres, the compact-source mercury-vapour lamp is very useful.7 To avoid stroboscopic effects, it is necessary to operate the lamp on D.C., which entails special starting and
Fig. 4. Marey's Apparatus, with Microscope, for the Study of small Insects in flight.
positioning is possible in three dimensions to one-tenth of a millimetre, with ease and certainty.
Lighting Problems
Recent developments in gas-discharge lamps, for example, the Mole-Richardson " Cineflash " equipment,6 have solved some of the problems of lighting large areas, but this apparatus is not suited for small objects. For small fields, one of the most convenient arrangements is to use high-wattage lowvoltage filament lamps in efficient reflectors,
control circuits, but the very high brightness, small area, and lack of heat make the equipment indispensable for many types of work. In addition, the author also uses a small D.C. arc focused accurately on the object. The arc generates some heat, but it is easily removed with suitable filters, and with both lamps in use at the same time, no heating troubles have been met with. The two lamps will illuminate an area 3 mm. x 5 mm. to an estimated brightness of about 175,000 footcandles.
In lighting very small machine parts, some