There are a lot of us out there with 1D Mk XX and are often torn between which lens to pick up. Most lenses are either designed for crop APS-C (1.6x on Canon) or Full frame. The 1.3 crop factor of the 1D can sometimes make choosing lenses a bit of a conundrum.
I hope we can get a thread going where all the good folks who have a 1D can maybe try to put a lens designed for APS-C on their 1D and check if it works.
Please post pictures of your APS-C lens on APS-H sensor results along with your thoughts of how the combination would work together.
I don't think I need to say this, but don't put EF-S lenses on your 1D. This thread is mainly for third party lenses.