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Double Convex Lens


A double convex lens, also called biconvex (or simply convex) lens, is a slab of optically active medium, usually glass, bounded by a convex spherical surface on either side. A widely known, everyday use for such a lens is a magnifying glass. The convex lens possesses the ability to focus down parallel light rays to a focal point.


This lens is used in the Michelson Interferometer Experiment where lenses are required for two purposes . The first lens which the LASER beam encounters forms spherical wavefronts of the planar ones emitted by the LASER. In general, all wavefronts are spherical; however, sometimes the radius of curvature of the wavefronts can be so large that it can be considered a plane, for all intents and purposes – similar to how the curvature of the Earth is hardly noticeable from our perspective. This curving of the wavefronts forms rings of interference instead of fringes. The second lens encountered by the beam simply enlarges the image of the pattern, making it easier to see as it is projected onto the screen.

Mounting Options

The K-Optics convex lens is mounted on a round 25 mm holder.

Technical Specifications

Table 2: Technical specifications for K-Optics convex lens. All dimensions given in mm.
Table 2: Technical specifications for K-Optics convex lens. All dimensions given in mm.

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  • Double Convex Lens: 25 mm Diameter, 25 mm Focal Length  - Specification Page: Download

Theoretical Background

All lenses are modeled by the lensmaker's equation:

Where R_1 and R_2 are radii of the first and second surfaces encountered by the light, respectively. The convention for convex lenses is that R_2<0. For a sufficiently thin lens, compared to the radii, the thin lens equation applies:

Such a lens forms images according to the imaging equation:

In this equation, u is the position of the object and this is always positive, while v is the position of the image and it is negative when on the same side as the object.

The following is a table to categorize the various scenes shown above: