  The electronic response of doped manganites at the transition from the
paramagnetic insulating to the ferromagnetic metallic state in $\rm
La_{1-x}Ca_{x}MnO_3$ for $\rm (x=0.3,0.2)$ was investigated by dc conductivity,
ellipsometry, and VUV reflectance for energies between 0 and 24 eV. A stablized
Kramers-Kronig transformation yields the optical conductivity and reveals
changes in the optical spectral weight up to 24 eV at the metal to insulator
transition. In the observed energy range, the spectral weight is conserved
within $\rm 0.3 %$. The redistribution of spectral weight between low and high
energies has important ramifications for the down-folding of low-energy
Hamiltonians. We discuss the importance of the charge-transfer, Coulomb onsite,
Jahn-Teller, and screening effects to the electronic structure.
