Comparing Chromatic Aberration Quantitatively?

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SUMMARY

This discussion focuses on quantitatively comparing chromatic aberration between two lens systems used in astronomy: a telephoto lens and an objective lens from binoculars. The author suggests using colored lasers to measure refraction angles as a method for this comparison. Key concepts include transverse and longitudinal chromatic aberration, which can be assessed through a 'star test' involving imaging point sources at various wavelengths (656.3 nm, 587.6 nm, and 486.1 nm). The discussion emphasizes the importance of precise measurement conditions, including image and object distance, field height, and f/#.

PREREQUISITES
  • Understanding of chromatic aberration types: transverse and longitudinal
  • Familiarity with basic optical principles and lens systems
  • Knowledge of spectral lines and their significance in optical testing
  • Experience with experimental setups for optical measurements
NEXT STEPS
  • Research methods for conducting a 'star test' to evaluate chromatic aberration
  • Explore the use of colored lasers for optical measurements in astronomy
  • Learn about the impact of f/# on optical performance and aberration
  • Investigate the characteristics of compact fluorescent sources as spectral lines
USEFUL FOR

Astronomy enthusiasts, optical engineers, and anyone interested in understanding and measuring chromatic aberration in lens systems.

mishima
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Hi, I have 2 similar lens systems used for basic astronomy (as refracting telescopes). The first is a telephoto lens designed for a camera and the second is the main objective of an old pair of binocs paired with an eyepiece in a tube. I am suspecting the former exhibits more chromatic aberration just based on some observations of the moon and bright stars.

I was wondering if there is an experimental setup I could perform, even crudely, on my workbench tabletop that would allow me to compare the chromatic aberrations of both systems quantitatively.
 
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If you have two different colored lasers, you can measure their refraction angles.
 
mishima said:
I was wondering if there is an experimental setup I could perform, even crudely, on my workbench tabletop that would allow me to compare the chromatic aberrations of both systems quantitatively.

As with any optical test, the details matter: image and object distance, field height, f/#... There are two 'flavors' of chromatic aberration- transverse (or lateral) and longitudinal, and these are independent.

Start with the standard spectral lines: 656.3, 587.6, and 486.1 nm. If you don't have access to a 'clean' spectral source, you can probably use a compact fluorescent source. Use of a broadband source (sunlight) will make the measurement more difficult.

The simplest measurement is a 'star test': image a point source and compare the locations of the image at different colors: transverse chromatic will shift the image from side to side, while longitudinal will shift the focal plane along the optical axis. Note that typical chromatic aberrations in a reasonably corrected lens will give displacements on the order of microns. Imaging the 'star' at different field heights and stop sizes will characterize the system.
 

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