Before revision: For this reason, athermalization is often achieved by using switchbacks or in-depth knowledge of the thermal elastic effects that are present in the particular system .
After revision: For this reason, athermalization is often achieved by using switchbacks , where a compensating element (generally of higher CTE than the mounting structure material to minimize the mass of material needed) is mounted in such a way so that as it expands, it expands in the opposite direction of the mounting structure's expansion, thereby negating it and holding the lens or optical element at a fixed position over a given temperature range .