Canon EOS cameras are popular with astro-imaging enthusiasts. But, the typical T-ring / telescope setup does not take advantage of the wide aperture of the Canon bayonet mount: significant vignetting is caused by the constriction of the T-ring opening. Canon Wide T Adapter with Bayonet for 2.4" connects to your EOS in place of the T-ring and provides 25% greater aperture to minimize vignetting