Alens system has a back vertex power of +5.00 d, a neutralizing power of +4.00 d, and an equivalent power of +10.00 d. the back surface is in water and the front surface is in air. locate the six cardinal points this means when parallel light comes in power leaving back focus @f. we use it to find back vertex to secondary focal ph- remember n 1.33 is +5 and wil fr .fe-nya. -lu /woo : t400 d low) ^+" ; l. syカ0いこ+0-8 3 m ,ire -0.1or 0.133 n: 0.033 l: 10-133 pn t0.033 p t. 033m