The reason the 2nd one is brighter is the ISO is 16 times more but the shutter speed is only 4000/800 = 5 times more.
So these two photos have been taken with a different exposure!
So lets change the first one to 1/250 and f/11 ISO 100 and the second one to 1/4000 and f/11 ISO 1600 they would be much closer.
Does that make sense?
It is a very important concept - getting the exposure triangle right!
Refer 2nd post in this thread: http://www.ausphotography.net.au/for...ad.php?t=24050