In electron microscopy (Frank (1992)) one is faced with the case
for some 
where 
. 
does not satisfy Orlov's condition, and (3.9) cannot be
satisfied since 
for some 
. In that case we put
With this choice of v, (3.8) is the minimal norm solution of Pf = g. A proper discretization along the lines of section 2.1 leads to the weighted backprojection algorithm of electron microscopy, see Frank (1992).