Me2
New Member
The effective exposure time of the human eye is under 0.1 seconds (try opening and closing your eyes within 0.1 seconds, you can still see stars). The longest Hubble UDF exposure was effectively ~350,000 seconds. So the exposure multiplication is (conservatively) 3.5 million.
So if we accept the OPs figure of 127,551, that means the Hubble gets 450 billion times as much light as the human eye during the combined exposure.
Aha, here it is. 0.1 seconds.