User`s manual

Biaxial Displacement Follower User’s Manual Version 1.4, April 19, 2004 IM1013
Page
8
Example
The lens to be used in this example is the 105mm enlarging lens supplied with the system.
1 Assume that the object under study is expected to exhibit a peak-to-peak displacement of one inch.
2 Calculate the magnification:
A = 0.15 in. = 0.15 in
= 0.15
MR in 1 in
3 Calculate the working distance,
WD = (1 + 1/A) fl = (1 + 1/0.15) X 105 mm = 805 mm
If you prefer to have the working distance in inches, multiply by 0.03937 to obtain 31.69 inches.
4 Calculate the distance from the lens to the photo cathode.
D = (1 + A) fl = (1 + 0.15) X 105 mm = 121 mm
5 Calculate the length in millimeters of the extension tube needed by subtracting the internal distance between the
photo tube and the faceplate.
EX = D - 34.6mm = 121mm - 35.6mm = 86.4mm
Precision of the Lens Calculations
Often, the calculated values for the working distance and the tube length do not correlate well with experimental results.
There are many reasons for this, ranging from the tolerances built into the lens and tubes during manufacture to the
limitations of the simple lens formulas used in the calculation. Even the best lens has a finite thickness and is mounted in
some way within a lens holder. Most single-focus lenses are made up of more than one piece of glass; the pieces of glass
combine to make one lens with the rated focal length.
Figure 6
A simplified drawing of the 105mm lens used in the previous numerical example.