Made of polished glass with ground edges, each is 38 mm in diameter. The biconvex lenses have two outward curving symmetrical faces. They can be used as magnifying or condensing lenses. The biconcave lens has two inward curving symmetrical faces. It has a focal length of 50 mm and can be used for spreading out light. The biconvex lenses are available with a focal length of either 100 mm or 200 mm.
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