Question about Sigma 105mm, f/2.8 EX DG OS HSM, Canon EF

Especially in low light, the AF sometimes has a bit of trouble focusing, so I have to help it manually from time to time. But that doesn't happen often. Otherwise the AF works very well in general, but the lens is rather noisy (cracking etc.) In auto mode there is an error message, but you can easily fix it with Google. Unfortunately, I can't give you any information about the RF adapter.