#1 extension tube calculations

[Victor Polozov]

I bought Kenko extension tube set, and found some
formulaes in the instruction:

Image Magnification Ratio = ( Length of Extension Tubes
+ Master Lens Advance Volume ) / Master Lens Focal
Length

Exposure Factor = ( 1 + Image Magnification Ratio ) ^ 2

Master Lens Advance Volume = ( Master Lens Focal
Length ) ^ 2 / ( Master Lens Distance Reading - Master
Lens Focal Length )

Field Coverage = Image Size on Film Surface / Image
Magnification Ratio

May be you are interesting in implementation this feature
calculation.

PS:
I'm using ca on my Sharp Zaurus SL5500 (OZ 3.5.2.)