D800 iso query ?

Need advice please, on the D800 there are 3 choices of lower iso settings;

Lo.3
Lo.7
L1.0

Can anyone explain what each do please ? Thanks.

These are the "expanded iso" values below iso 100. L1.0 is iso 50, the other two are partial stop values between iso 50 and iso 100 (iso 64 and 80). Keep in mind that these are actually "pulled" iso 100 so the DR and IQ may not be as good as what you will get at the camera's base iso of 100.

Those are 0.3 stop, 0.7 stop, and 1.0 stop lower than the base ISO 100. More or less equivalent of ISO 80, 64, and 50. Same effect as lower ISO, but they cannot call them that because of the necessary method to go below the base. Not exactly the same - The dynamic range is also lowered, and there can be a little less contrast. May not be noticeable.

What they said. Essentially for very bright situations where you need to shoot at a given aperture and just can't get there at ISO 100 and the available shutter speeds. As was mentioned, you will technically lose some level of IQ, but it may not be noticeable. It definitely won't be as good as native ISO (100), so don't go there unless you need to as you're better off shooting at 100.