[Chimera-users] writing MRC maps

I have an MRC map that is 800^3. I do a color zone and split the map, generating eight maps, each 800^3. The first of the split maps I throw away, the volume of interest of the other seven maps is 50^3 each. How do I save the seven maps not at 800^3, but reduce their size to 50^3? thanks, Matt