Methods and equipment for recording small and sometimes rapid motions by photographic means are described, and the efficacy of photographic recording in such instances is evaluated. The optical system consisting of the light source, the mirror or prism for transmitting motion to the emergent beam, and a means of bringing the rays into focus on the film are discussed.
Attention is given to the critical issue of mirror mounting.
The film holder and the driving motor for the recording drum are described in detail. The authors conclude that the optical methods they describe are far more satisfactory than the recording pen, in compactness, in high natural period, and in elimination of friction. Costs are similar to mechanical methods. The development and reproduction of the record is an added complication, but the ease of duplicating the records is a decided advantage.