Also focometry. [f. as prec. + Gr. -πετρία measurement.] Measurement of focal distance.
1881. G. R. Piggott, in Nature, No. 622, 28 Sept., 515/2. If now an over-corrected lens were substituted, the diffraction rings ascended and the nebulosity descended: they exactly changed positions as regards focimetry.
1891. S. P. Thompson, in Proc. R. Soc., XLIX. 19 Feb., 225. Few of the accepted methods of focometry take into account the distance between the two principal points (or Gauss points) of a lens, or afford the means of measuring this distance, as well as the true focal length, and some of them are open to the objection that they necessitate troublesome double adjustments.
