power 4dAnyway coming to your question the requirement of +- 4D for a job means that the eyesht of an applicant should not exceed these values that is +4D and -4D and in other6. A convex lens of power +6 D is placed in contact with a concave lens of power –4D. What will be the nature and focal length of this combination ? (a) convex, 100 cm (b) convex, 50 cm