1. The problem asks: What type of lenses are used in binoculars and why? 2. Binoculars use **convex lenses** (also called converging lenses) in their optical system. 3. The formula related to lenses is the lens formula: $$\frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}$$ where $f$ is the focal length, $d_o$ is the object distance, and $d_i$ is the image distance. 4. Convex lenses are used because they converge light rays to a focal point, allowing the binoculars to magnify distant objects. 5. Convex lenses produce real, inverted, and magnified images which are then corrected by the binoculars' prisms to appear upright. 6. This magnification helps users see distant objects clearly, which is essential for binoculars. 7. In summary, convex lenses are chosen for their ability to focus and magnify light, making distant objects appear closer and clearer.