What are infinity optics on a microscope?

microscope optics

Microscopes with infinity corrected optical systems have infinity image distance.

These systems are designed by placing a tube lens within the body tube between the objective and the eyepieces, resulting in an intermediate image. This optical system permits optical accessories such as illuminators to be placed into the light path between the objective and the tube lens (also known as the infinite space) with minimal effect on focus and increase the tube length to greater than 160 mm. Infinity corrected optics are used in research laboratory microscopes and industrial metallurgical microscopes.

What are infinity optics?

Infinity optics are the production of a flux of parallel light rays after passing through the objective. This is different than the infinity space.

infinity optics

About the tube length

The tube length, or focal length, in infinity corrected optical systems ranges from 160 to 200 mm. The Royal Microscopical Society standardized microscope tube length at 160 mm during the nineteenth century and was the standard until the 1980s when infinity corrected optics were introduced. To adjust for this change, manufacturers needed to place additional optical elements into the accessories to restore the 160 mm tube length, resulting in reduced light and increased magnification. Microscopes without infinity correct optics have a specified tube length.

Benefits of infinity space

  • When accessories are added into the optical path, parfocality between different objectives can still be maintained.
  • Accessories can be designed to produce 1x magnification without altering alignment between the objective and tube lens. Optical accessories placed into the infinity space do not shift the location or the focal point of the image. This allows one to use a combination of optical techniques to compare specimens.

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