User`s manual

Biaxial Displacement Follower User’s Manual Version 1.4, April 19, 2004 IM1013
Page
7
Figure56
WD = Working Distance, MR = Full scale Measurement Range, fl = Focal Length of Simple Lens,
EX = Length of Extension Tube needed, D = Distance from lens to Photo Cathode,
A = Magnification (usually < 1)
To calculate the size of the extension tube needed:
1 Estimate the expected full-scale displacement for the target under study
2 Calculate the magnification
A = 0.15 in
MR in
or
A = 3.775 mm
MR mm
3 Calculate the working distance
WD = (1+1/A) fl
Focal length is most often given in millimeters, causing the calculated working distance to be in millimeters as
well. To convert the working distance from millimeters into inches, simply multiply by 0.03937:
WD (in.) = WD
(mm) X 0.03937 (in/mm)
4
Calculate the distance from the lens to the photo cathode
D = (1 + A) fl
5 Calculate the length in millimeters of the extension tube needed
EX = D - 34.6 mm