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Re: [ccp4bb]: 3Fo-2Fc maps

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Stefano Trapani wrote:
> So, can I say (very crudely) that a (3mFo-2DFc) map is better than a
> (2mFo-DFc) map, in that

Well, let us put it in this way,

In a (3mFo-2DFc) map, we have Fo + 2 (Fo-Fc) ( for simplifying the question,
it is not weighted). And in a (2mFo-DFc) map, we have Fo + 1(Fo-Fc).
Therefore, in the (3mFo-2DFc) map, the differences is doubled and the
unknown part of the structure is more evidant. But at the same time,
the bias is bigger. 

So, for a well final structure, I would prefer using (2mFo-DFc) map
which has less bias to show my result. And during model building,
I would prefer to use both maps and incline to (3mFo-2DFc) map.

Any other explanations? I would like to hear.

Songlin Li, Ph.D.
Dept. Microbiology
University of Alabama at Birmingham
AL35294, USA
Email: songlin@credit.cmc.usb.edu