It is not just at the focal point but multilayered lenses can be destroyed as the expand and contract and heat is emminated from the join and also Any lense w

It is not just at the focal point but multilayered lenses can be destroyed as the expand and contract and heat is emminated from the join and also Any lense with coatings to correct for chromatic abberation, the coatings get destroyed on the surface of the lenses just by being pointed at the sun.