The actual operation of SPCONVOL is completely automatic. The example here gives the most likely scenario for its use,
Convolving a response in a dataset 'image' with a gaussian of FWHM 1 pixel,
> crepsf psf=analytic mask=gaussian aux=1 pixsize=1 radius=6
out=gauss_kernel
> spconvol image gauss_kernel
Note that SPCONVOL ignores the axis units of the source image,
and assumes that the pixels are the same size as those defined
in the spatial response.