SET of 3 mounted ACHROMATS (2 negative, 1 positive) Description: SET OF 3x ACHROMAT LENSES (seem to belong to laser project). Set comprises 3 lenses only (I have 2 sets available, that's why you see 6 lenses in pictures). They are described as follows: Mounted 9mm lens NEGATIVE achromat lens (with holes for easy screwing with appropiate lens removing tool). This mounted lens is then screwed in a brassed sleeve (focal length unknown, seems a bit less powerful powerful effect than 11,5mm). Sleeve details: 17,80mm diameter / 16mm length / M16 inner thread size / M2 locking allen screw (included). Mounted 11,5mm lens NEGATIVE achromat lens (with holes for easy screwing with appropiate lens removing tool). This mounted lens is then screwed in a brassed sleeve (focal length unknown, seems more powerful effect than 9mm). Sleeve details: same as above. Mounted 13,5mm lens POSITIVE (not sure if achromat lens, it seems two plano-convex lenses confronted in their convex side so that the "plano" side comes out at each side). No brassed sleeve. Everything works smooth (the screwed lens screws easily up and down the sleeve and the locking screws work properly). Lenses are clean overall. Remember "negative" lens means "barlow" effect in the optical train and "positive" the contrary. Issues: some normal usage marks.