Roy

Thank you, I think I read it incorrectly. I have messaged the OP with the below update........ I think my answer to your post may have confused the issue. The 70-350 will vignette in full frame mode, you would have to have it either on auto apsc mode or change it to that in the menu. It will then have no vignetting and give you approx 105-525 eqv. You will 'only' have 26 megapixels then but as Mark Galer says that is still more than most APSC cameras It's a great sharp lens and light to carry. I hope this corrects my post. It has been pointed out to me that I didn't answer your question correctly

That's quite correct I have it on auto apsc, so if I attach a crop sensor lens it goes into crop mode automatically. Why would it be set to any other way?

what adapter do you use

I use this often on my A7R4 no vignetting at all, sharp and fast to focus I recently started an album on this combination on my flickr account link below 70-350 album

A7R4 100-400 GM lens (400mm in crop mode 600mm eqv)