A novel autocollimating method for measuring the focal distances is presented. It may be used for measuring the focal distances of lenses and single optical elements in the visible, infrared and ultraviolet range. The relative uncertainty of this method is about 0.1%. The limited uncertainty is over 0.03%.
Alexandr G. Ershov,
"A novel autocollimating method for measuring the focal distances", Proc. SPIE 9526, Modeling Aspects in Optical Metrology V, 95261B (21 June 2015); doi: 10.1117/12.2179360; https://doi.org/10.1117/12.2179360