I was just glancing through my Kodak Professional Photoguide (3rd edition, 1998) and found an entry on close-up exposure (pp. 46 - 47) which confirms that the usual formula does not work with retrofocus or telephoto lenses. Kodak suggests a formula for these lenses:

Exposure factor = (M/P + 1) ²

where

M = Magnification

P = Pupillary magnification

P is calculated as rear exit pupil diameter divided by front entrance pupil diameter (so it is specific to a particular lens).

Will send PDF file of these pages to anyone interested.

Regards,

David