Infinity-Corrected Optics
Definition
An objective design in which the back focal plane produces a collimated (afocal) beam rather than a converging beam, allowing optical elements to be inserted in the parallel-beam path without introducing aberration.
- Field
- Optical microscopy
- Beam path
- Collimated, afocal, between objective and tube lens
- Advantage
- Allows accessories in the parallel beam without aberration
Common questions
Why can filters, polarisers, or beamsplitters be inserted into an infinity-corrected microscope's optical path without ruining focus?+
Because the light between the objective and the tube lens travels as a parallel, collimated beam rather than converging toward a real image, inserting a flat optical element there shifts the beam only slightly rather than introducing the focus-disrupting aberration it would cause in a finite-conjugate design.
How does infinity correction change what a tube lens does compared to older finite-tube microscopes?+
In an infinity system the objective alone does not form the final image, so a separate tube lens is required to refocus the collimated beam into a real image at the eyepiece or camera, whereas finite-conjugate objectives formed the image directly at a fixed distance without needing that extra lens.
Related terms
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- ASTM E766
- The ASTM International standard practice for image-scale calibration in microscopy, extended by OSAC to govern optical microscope calibration in US forensic trace-evidence...
- Depth of Field
- Axial thickness of the specimen that appears acceptably in focus at one time. High in stereoscopic microscopes, very low in oil-immersion compound...
- Empty Magnification
- Magnification beyond approximately 1000 times the objective NA; enlarges the image without adding resolvable structural information, producing blurred detail that can be...
- ISO 8576
- The ISO standard governing the accuracy of stage micrometers and reticle eyepieces, specifying Class I and Class II tolerance levels traceable to...
- Koehler Illumination
- The standard illumination method for research microscopy in which the light source is focused at the condenser back focal plane, producing uniform...
- Numerical Aperture (NA)
- The product of the refractive index of the medium between objective and specimen and the sine of the half-angle of the maximum...
- Parfocality
- The property of an objective nosepiece turret such that switching objectives keeps the specimen approximately in focus without re-focusing; defined by ISO...
- Plan Objective
- An objective corrected for field curvature so that the entire image field is simultaneously in focus; required for photomicrographic evidence documentation to...
- Rayleigh Criterion
- The condition that two point sources are just resolved when the central maximum of one Airy disc coincides with the first minimum...
- Stage Micrometer
- A calibrated glass slide with a ruled scale of known spacing (typically 0.01 mm divisions), used to establish the pixels-per-micrometre calibration factor...