Huygenian design consists of two plano-convex lenses positioned with both convex faces toward the object. Designed for use with low power achromatic objectives. Our entire line of eyepieces will fit any international standard microscope with a 23mm inner diameter eyepiece tube.DIN format: magnification of eyepiece determined using a 160mm tube length. Based on the German standard.JIS format: magnification of eyepiece determined using a 170mm tube length. Based on the Japanese standard.Note: Total magnification of a microscope will only be the product of the eyepiece and objective powers, if both are designed for the same tube length. If mismatched, re-calibration is required.Eyepieces sold individually.