Ok, Shining 3D tech support explained me:

Quote Originally Posted by Hugues View Post
Questions on manual scan mode (without turntable):

- in the 2 object pictures below, there are parts highlighted in red, does it mean anything special ?
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Yes, it means your object is overexposed. Change the brightness parameter in the Einscanner software (menu Describe your object) so that you have only a little bit of red


Quote Originally Posted by Hugues View Post
- the projector always displays a black horizontal band across the scan window, quite large, it seems to interfere with the scan, meaning the part covered by the band don't scan as well as the rest of the part, i think. In "turntable mode", i don't have this black horizontal band.
This large horizontal black band is not normal. If you see it, restart the scanner.

Instead, in manual mode, you should see a thin black cross. This is to help you align the scanner with your object, also to focus your scanner on the object. Move your scanner backward or forward until the cross is sharp.