I'm trying to accomplish what is probably very simple. I'm using a physical camera, with f-stop and focal distance, to focus on a small object with reflectivity. I'd like to start, however, focused on what is being reflected off the object. Easy - just set the focal distance to be the combined distance between the object, and the reflected object.
But what do you do if the reflected object is an HDRI sky object? It seems like it has an infinite focal distance. How can I focus on the sky, while still having the foreground object nice and blurred?
Just to circle back here for future readers - what Adam suggests is probably the only working solution. I didn't want to go this route because it'd mean I'd be rolling the dice for how the reflections currently lined up. But ditching the Sky object and going with a Sphere was the only workaround for focal distance - so I bit the bullet.