“The Effect of Air Gap Width (S) and the Ratio (P1 D2) on .Minimum Projector Focal Length (Fp)min for the Double Pole-Piece Lens- at Costant Excitation (NI)”. Ibn AL-Haitham Journal For Pure and Applied Sciences 21, no. 3 (September 23, 2017): 95–111. Accessed July 16, 2024. https://jih.uobaghdad.edu.iq/index.php/j/article/view/1412.