A lens for image pickup is provided in which various aberrations are corrected satisfactorily, the optical length is at maximum approximately 6 mm, and moreover a sufficient back focus is secured. The washer assembly is polyaxially pivotable relative to the screw. an amine type extractant is obtained by adding an aqueous solution containing a sulfite ion to an amine type extractant and stirring the mixture and reducing a ferric chloro complex ion to divalent.