Complex sentence: In other words, the negative lens can be as strong as the outer two combined, when one measures in dioptres, yet the lens will converge light, because the rays strike the middle element close to the optic axis.
Split into simpler sentences: In other words, the negative lens can be as strong as the outer two combined, when one measures in Dioptres. Yet the lens will converge light, because the rays strike the middle element close to the optic axis.