A mirror system including a primary mirror, and a secondary mirror with different coefficients of thermal expansion. A negative CTE strut can include a main body portion, a first coupling portion and a second coupling portion disposed opposite one another about the main body portion and defining a strut length. The first and second coupling portions can each interface with an external structure. The negative CTE strut can include an offsetting extension member having a first end coupled to the main body portion and a second end coupled to the first coupling portion by an intermediate extension member. The first and second ends can define an offset length parallel to the strut length. When the negative CTE strut increases in temperature, the offset length can be configured to increase due to thermal expansion of the offsetting extension member sufficient to cause the strut length to decrease.