Simple Lens Approximations
For the plano-convex lens, the focal length equals twice the radius of the convex surface. This is also true for the plano-concave; howerver, since the radius is negative, this results in a negative focal length: f = 2R |
For other forms of simple lenses, the following applies
| (Note: 0 = power): | 1
EFL | = 0 = | 1
2 | [ | 1
R1 | - | 1
R2 | ] |
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For the double-convex or double-concave lens having equal radii, the focal length will equal the radius: R1 = R2 = f |
If two or more thin lenses are stacked close together, their powers (1/EFL) may be added:
| 0(1+2) = 01 = 02 = f(1+2) = | f1 * f2
f1 + f2 |
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If a substantial separation "d" exists between lenses, then:
| f(1+2) = | f1 * f2
f1 + f2 -d |
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