Real World Lenses  Todd Cherniawsky 
Matching lens size to real world cameras is imperative when you are working with back ground plates. The following tips and tables will help Imagineers greatly.
16mm LENSES 16 = 16mm lens equivalent (mm)H = Horizontal Field of View (degrees) Y = Imagine Camera Size : Y value (Imagine Units) NOTE To convert any 16mm lens to Imagine Y Units, multiply the lens focal length by 33.3333. 

35mm LENSES 35 = 35mm lens equivalent (mm)H = Horizontal Field of View (deg) Y = Imagine Camera Size : Y value (IMU) NOTE To convert any 35mm lens to Imagine Y Units, multiply the lens focal length by 15.2381. 

LETTERBOXED Z VALUES LAR = Letterboxed Aspect RatioZ = Imagine Camera Size : Z value (IMU) 
Here is a short table of aspect ratios and their closest pixel count equivalents:
FORMAT  ASPECT RATIO  WIDTH  HEIGHT 
Academy  1.33 : 1  640  480 
VistaVision  1.50 : 1  640  426 
European Distribution  1.66 : 1  640  386 
IMAX, Super16mm  
American Distribution  1.85 : 1  640  346 
Anamorphic Squeeze  2 : 1  640  320 
70mm  2.20 : 1  640  290 
Super Panavision  2.34 : 1  640  274 
35mm Anamorphic  2.40 : 1  640  266 