def set_maxrad(self,newrad):
        """
        Sets max allowed radius in populations.

        Doesn't operate via the :class:`stars.Constraint`
        protocol; rather just rescales the sky positions
        for the background objects and recalculates
        sky area, etc.

        """
        if not isinstance(newrad, Quantity):
            newrad = newrad * u.arcsec
        #if 'Rsky' not in self.constraints:
        #    self.constraints.append('Rsky')
        for pop in self.poplist:
            if not pop.is_specific:
                try:
                    pop.maxrad = newrad
                except AttributeError:
                    pass