Kitchener says a 1-3/4-inch object-glass should show Rigel double; in earlier editions of his work he gave 2-3/4-inches as the necessary aperture.

Smyth mentions Rigel as a test for a 4-inch aperture, with powers of from 80 to 120.

A 3-inch aperture, however, will certainly show the companion.

Rigel is an orange star, the companion blue.
Turn next to [lambda] the northernmost of the set of three stars in the head of Orion.

This is a triple star, though an aperture of 3 inches will show it only as a double.