Features Professional Manufacturing: This lens is coated with high light transmittance, with high refractive index, and the image is brighter. Automatic Rebound: Spring protection device, the achromatic objective can automatically rebound when touches the cover glass during observation to protect the lens from crushing the specimen. Premium Brass Material: The achromatic objective is made for brass material, fine workmanship, corrosion and fall prevention, exquisite and durable, chrome plated accuracy material for the shell. Wide Application: The screw interface size is the international standard RMS size, which can be used by most professional biological microscopes on the market. Standard Specification: This lens has a magnification of 20X, common rail distance of 195mm, and parfocal distance of 45mm. Specification: Item Type: Achromatic Objective Model: 20/0.40 Material: Brass Use: Microscope Accessories Interface Size: Approx. 20.2mm / 0.80in (International Standard RMS Size) Magnification: 20X Numerical Aperture: Approx. 0.40mm / 0.02in Cover Glass Applicable Thickness: Approx. 0.17mm / 0.006in Microscope Applicable Mechanical Tube Length: Approx. 160mm / 6.30in Working Distance: Approx. 0.55mm / 0.02in Common Rail Distance: Approx. 195mm / 7.68in Parfocal Distance: Approx. 45mm / 1.77in Spring: Yes (Automatic Rebound) Package List: 1 x Achromatic Microscope Objective 1 x Storage Box Package List 1 x Achromatic Microscope Objective 1 x Storage Box