Microscopy Primer
Light and Color
Microscope Basics
Special Techniques
Digital Imaging
Confocal Microscopy
Live-Cell Imaging
Photomicrography
Microscopy Museum
Virtual Microscopy
Fluorescence
Web Resources
License Info
Image Use
Custom Photos
Partners
Site Info
Contact Us
Publications
Home

The Galleries:

Photo Gallery
Silicon Zoo
Pharmaceuticals
Chip Shots
Phytochemicals
DNA Gallery
Microscapes
Vitamins
Amino Acids
Birthstones
Religion Collection
Pesticides
BeerShots
Cocktail Collection
Screen Savers
Win Wallpaper
Mac Wallpaper
Movie Gallery

Infinity-Corrected Optical Systems

In modern research-grade microscopes equipped with infinity-corrected optical systems, the objective no longer projects the intermediate image directly into the intermediate image plane. Instead, the objectives are designed so that light emerging from the rear aperture is focused to infinity, and a second lens, known as the tube lens, form the image at its focal plane. Light rays exiting the infinity-focused objective lens are collimated, so that beamsplitters, polarizers, Wollaston or Nomarski prisms, vertical illuminators and other components requiring a parallel beam can be easily introduced into the optical pathway. After passing through these auxiliary optical devices, the parallel light beam is made to converge and form an image by the tube lens. Unlike the situation with fixed-tube optics, magnification of the intermediate image in infinity optical systems is calculated by the ratio of focal lengths between the tube lens and objective. Because the focal length of the tube lens varies betwen 160 and 250 millimeters (depending upon the manufacturer), the focal length of the objective can no longer be assumed to be 160 millimeters divided by its magnification.

Introduction to Infinity Optical Systems - Over the past 10 years, the major microscope manufacturers have largely all migrated to the utilization of infinity-corrected optical systems in both research-grade biomedical and industrial microscopes. The basic optical components of an infinity system are the objective, tube lens, and the eyepieces. For observation, a specimen is placed near the front focal plane of the objective, which gathers light transmitted through or reflected from the central portion of the specimen and produces a parallel bundle of rays projected along the optical axis of the microscope toward the tube lens.

Nikon CFI-60 Specification - Examine Nikon's new CFI-60 specification for the optical systems currently being offered in the company's line-up of infinity-corrected microscopes and objectives. Featuring a tube lens focal length of 200 millimeters and an expanded objective thread size, these microscopes also have a 60-millimeter parfocal distance, the longest in the industry. Together, these advanced specifications enable the utilization of longer working distance objectives having some of the highest numerical apertures currently available.

Interactive Java Tutorials

Tube Lens Focal Length - As the focal length of the tube lens is increased, the distance to the intermediate image plane also increases, which results in a longer overall tube length. Tube lengths between 200 and 250 millimeters are considered optimal, because longer focal lengths will produce a smaller off-axis angle for diagonal light rays, reducing system artifacts. Longer tube lengths also increase the flexibility of the system with regard to the design of accessory components. This interactive Java tutorial explores the effect of tube lens focal length on the angle of off-axis light rays in microscopes with infinity-corrected optical systems.

Objective Magnification in Infinity Optical Systems - Infinity-corrected microscope optical systems are designed to enable the insertion of auxiliary devices, such as vertical illuminators and intermediate tubes, into the optical pathway between the objective and eyepieces without introducing spherical aberration, focus corrections, or creating other image problems. In a finite optical system, light passing through the objective converges at the image plane to produce an image. The situation is quite different for infinity-corrected optical systems where the objective produces a flux of parallel light wavetrains imaged at infinity, which are brought into focus at the intermediate image plane by the tube lens. This tutorial explores how changes in tube lens and objective focal length affect the magnification power of the objective in infinity-corrected microscopes.

References

Selected Literature References - Gathered from our vast library of literature on optical microscopy, the reference materials listed in this section are an excellent source of additional information on infinity-corrected optical systems. Included in this section are references to review articles, original research reports, and book chapters that discuss various aspects of the theory and applications regrading how microscopes are configured to take advantage of infinity optics.

Contributing Authors

Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.

Kenneth R. Spring - Scientific Consultant, Lusby, Maryland, 20657.

John C. Long and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.


BACK TO MICROSCOPE ANATOMY

Questions or comments? Send us an email.
© 1998-2022 by Michael W. Davidson and The Florida State University. All Rights Reserved. No images, graphics, scripts, or applets may be reproduced or used in any manner without permission from the copyright holders. Use of this website means you agree to all of the Legal Terms and Conditions set forth by the owners.
This website is maintained by our
Graphics & Web Programming Team
in collaboration with Optical Microscopy at the
National High Magnetic Field Laboratory.
Last modification: Friday, Nov 13, 2015 at 01:18 PM
Access Count Since December 27, 2000: 52706
For more information on microscope manufacturers,
use the buttons below to navigate to their websites: