What instruments lens is used?

The term "instruments lens" is not specific, but if you're referring to lenses used in optical instruments, common types include convex lenses, which converge light to form images, and concave lenses, which diverge light. These lenses are essential in devices like microscopes, telescopes, and cameras, allowing for magnification and image formation. The choice of lens depends on the desired application, such as focusing light or correcting optical aberrations.