Biomedical Engineering Reference
In-Depth Information
Crown
Flint
Achromatic doublet
FIGuRE 2.12
Achromatic. doublet. lens. to. compensate. for. chromatic. aberration. due. to. the. wavelength. depen-
dence.of.the.indices.of.refraction..Here.one.lens.is.biconvex.and.is.made.of.crown.glass.with.one.index.of.refraction,.
and.the.other.lens.is.plano.convex.and.is.made.of.lint.glass.with.a.diferent.index.of.refraction..he.lens.pair.tends.
to.compensate.for.the.dispersion.of.multiwavelength.light.
wavelength. dependence. of. the. index. of. refraction. is. called. dispersion,. since. it. causes. light. to. be. dis-
persed.into.its.spectral.components.
A.solution.to.overcome.chromatic.aberration.is.to.use.two.diferent.lenses.with.two.diferent.shapes.
(e.g.,.convex.and.concave.radii.of.curvature).made.with.optical.materials.with.diferent.dispersion.char-
acteristics.(e.g.,.crown.and.lint.glasses)..An.example.is.shown.in.Figure.2.12.
In.addition,.lenses.can.have.other.optical.aberrations.such.as.coma,.astigmatism,.ield.curvature,.and.
distortions.(barrel.and.pincushion)..Misalignment.between.optical.elements.can.cause.further.aberra-
tion.as.discussed.in.Chapters.4.and.9..While.the.primary.goal.of.adaptive.optics.in.biological.imaging.
is.to.overcome.sample-induced.aberrations,.as.discussed.in.Chapter.3,.the.adaptive.optical.system.can.
also. overcome. optical. system-induced. aberrations. due. to. aberrations. in. the. optical. components. and.
misalignments.between.components..In.some.situations,.system.aberrations.can.dominate.specimen-
induced. aberrations.. Here,. adaptive. optics. can. be. used. to. relax. system. tolerances. to. bring. down. the.
cost.of.high-performance.optical.systems.or.to.improve.the.performance.of.lower-performance.optical.
systems.
references
Feynman,.R..P.,.R..B..Leighton,.and.M..Sands,.
he Feynman Lectures on Physics
,.Addison-Wesley,.Reading,.
MA,.1966.
Born.M..and.E..Wolf,.
Principles of Optics
,.7th.ed.,.Cambidge:.Cambridge.University.Press,.2006.
