In simplified terms, a method for calculation the EFL (Effective Focal Length) of a lens train.
For stage purposes, For a two-lens system (such as that in many ERSs):
EFL= (f1*f2)/(f1+f2-d),
where
EFL=Effective Focal Length,
f1=Focal Length of Lens1,
f2=Focal Length of Lens2,
d=Distance between Lenses.
For more complete explanation, see the site Gullstrand's Equation.
For stage purposes, For a two-lens system (such as that in many ERSs):
EFL= (f1*f2)/(f1+f2-d),
where
EFL=Effective Focal Length,
f1=Focal Length of Lens1,
f2=Focal Length of Lens2,
d=Distance between Lenses.
For more complete explanation, see the site Gullstrand's Equation.
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