Discovery Crafts DGL 40 magnifying glasses. Discovery Crafts DGL 40 magnifying glasses are an optical device that makes working with small objects more comfortable. The interchangeable lenses offer five different magnifications and the in-built lighting illuminates the work surface effectively. This magnifier is a real find for the jeweller, watchmaker, model maker, restorer and many others. It will prove useful for professional use and hobbies.all lenses are made of optical polymer glass - a very strong material with high transparency. The image they provide is clear, high-contrast and razor-sharp. The lenses are attached to the spectacle frame, but cannot be combined with each other: only one lens may be used at a time. The lenses have a relatively wide viewing angle so that you can see with both eyes at the same time. If necessary, the temples of the spectacle frame can be removed and replaced with a textile headband, and there is a block with two LEDs in the centre of the frame. They are powered by batteries.