The nesting cavity is about 18 feet high. I had been seeing/hearing these guys in about an 80 acre bush all spring and started looking for their nest. I was surprised it only took a couple of hours to find it. They usually drill into a large, smooth-barked live tree on the south or east side at least 15 feet high. In that 80 acres there were not very many trees that suited their needs so it wasn't too hard to find.
I am assuming you have the cam on a nearby tree and are using a ladder or climbing stand to check it? Any problem with them swooping at you defending the nest? Very different, I am looking forward to future pics of nestlings.
I've mounted the camera on a mount I built out of 1 by 4. It is bunged to the tree 15 feet up and an offset section holds the cam about 30 inch's from the cavity. I'm using tree steps to access it which I remove to prevent easy access for the theives.