%N cnvlext %F $MIR/src/subs/cnvl.for
%D Determine the extent of the point-spread function, etc.
%P rjs
%: convolution, fft
%B
      subroutine CnvlExt(handle,n1,n2,n1d,n2d)

      ptrdiff handle
      integer n1,n2,n1d,n2d

  Return the size of the point-spread function, and the maximum sized
  input image that can be handled.

  Input:
    handle     Handle of the beam, previously returned by CnvlIniA or
               CnvlIniF.
  Output:
    n1,n2      Size of the point-spread function.
    n1d,n2d    Maximum sized input image that the CNVL routines can
               cope with for this beam
