The Hubble Space Telescope has a primary mirror with a diameter of 2.4 meters (7.9 feet). However, aperture refers to the diameter of the opening in the lens that allows light to pass through, and this is determined by the adjustable diaphragm within the telescope.

Hubble's effective aperture can be adjusted depending on the specific scientific observations being conducted. It can be as small as 2.4 meters (7.9 feet) or as large as 2.4 meters (7.9 feet), depending on the instrument being used and the desired field of view.

While the primary mirror size is fixed, the effective aperture is often adjusted for optimal performance in different observing scenarios.