A99 is equipped with a dual AF system.
And it needs much amount of light to drive the dual AF system than A77's AF system and any other Alpha.
I mean,A99 can't generate a picture with amount of light as much as D600.
and also,It is said that A77 needs 20~30% amount of light to drive AF.
but, A99 is not only equipped with basically phase detection AF system.
A99 has "on board" Phase detection AF system additionally.
As it see the NEX-5R's DxOmark score which is said to be equipped with on board phase detection AF system and NEX-5N which has same sensor as NEX-5R without on board phase detection AF system.
It indicates that on board phase detection AF system would need about 20% amount of light.
And then,considering all of these things,,That dual AF system would need about 40~50% amount of light to drive AF.
I heard that A99 has same sensor as D600.
D600's Low-Light ISO score is 2979.
A99's sensor can receive about only 60~50% amount of light,because of affection of light reduction from that AF system,
2979*(60~50%)= 1787 to 1490
Do you get it,guys?
A99's Low-Light ISO score is not doubtable score,I think.