When looking into a clear blue sky, no cloud, birds, trees or any object to give a frame of reference. When a person is actively looking, as opposed to day dreaming or gazing.The sky goes for a long distance, and with uninterrupted view, and I guess the first question would be:-  At what point into the atmosphere can the human eye see (which is not a topic for this site), following this,  What I want to know; is at what point to the eyes come to rest and How is the focal point determined?Another consideration is:How can this be measured? Would any attempt to measure this would involve putting a device between the eyes and focal point?
How is the focal point determined when looking into a clear sky?
vision