DIN Objective (Deutsche Industrie Normen) refers to an international standard for microscope objectives. This standard specifies the exact threading and focal length used to insures compatibility with lenses from other microscope manufacturers.
\r\nOil Immersion lens is a specially sealed lens that requires a drop of special oil on the subject for use. The oil is put on the cover slip and the objective is lowered into the oil. Used for very high magnification (1000x +), to compensate for the characteristics of light waves. When viewing something magnified 1000+ times has fewer light waves passing through the subject into the lenses. Immersion oil allows you to control and actually "bend" more of that light into the lens allowing you to see clearer.
\r\nAchromatic lens is specially designed and coated to correct for the occurrence of light separating into colors when passing through glass. An achromatic lens corrects this in such a way that colors appear more accurate after being magnified.\r\n