The thermal coefficient of expansion in steel is half of what aluminum isSuch as at a given temp, if steel is 11, then aluminum is 23.1Is this really a concern in telescope tube design? I understand that aluminum is 5% lighter.
Thermal expansion is only a concern if you are doing long-exposure astrophotography, where changing temperatures will require occasional refocusingEven so, most premium refractors use aluminum tubes, because it is lighter, easier to work, and doesn't rustAluminum also has an advantage in thermal conductivity - it is less prone than steel to differential thermal expansion.
