Sil, I fully agree with you.
To avoid miscalculations, for those who like formulas, I implemented the NPF rule in a form page. It is still in french but you can choose between 340 DSLR or Digital Backs from 15 brands (that's almost exhaustive) from 4/3" to medium format :
http://www.sahavre.fr/tutoriels/astr...file-d-etoiles