Experimental method to quantify chromatic aberration in telescope optics

[mishima]

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.

 

[Khashishi]

If you have two different colored lasers, you can measure their refraction angles.

 

[Andy Resnick]

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.