Hello Andrew,
May I ask you what are the autofocus configurations you're using for this lens on Fuji XT4? I simply cannot use it at all. The noise is very loud. The motor doesn't stop rotating even without any changes on distance to the subject. And when I change the subject, it makes abrupts jumps and remains hunting back and forth many times before stick to something. I thought it was due to incompatibility with XT4 + Fringer, but it seems that some people are getting way better results than me. So I'm start to thing my copy is faulty...
Cheers,
Mariana