Linen Tester with counter + LED (Large)

High quality metal linen tester with counter and shadow free LED light magnification: 6x biconvex glass lens (silicate glass) lens diameter: Ø 27 mm 2 LED open window/foot: 20x29 mm frame material: metal colour: black mm / inch scale dimensions: height 5.0 cm width 2.1 cm length 3.0 cm weight 154 grams synthetic leather pouch included Biconvex lenses are also called convexo-convex lenses and are mainly made out of a special quality glass. Different types of biconvex-lenses exist such as the planconvex-lens. The most common biconvex lens is the symmetric-convex lens as used in this magnifier. The biconvex lens is manufactured with identical convex surfaces each side of the lens. The focal length is equal to the radius of the curvature. Resulting from its perfect symmetry it produce images close to 1 and up to a magnification of 8x. Biconvex lenses have positive focal lengths and form both real and virtual images. Aberrations such as coma, distortion, and chromatic aberration almost exactly cancel out also due to the symmetry.