All achromats will have similar percent chromatic aberation. It amounts to a defocus of approximately .06% of the focal length. This means that for a 1000mm focal length, the blue and red will focus 0.6mm farther than the green. The longer the focal ratio, the closer this will be to the 1/4 wave limit of a diffraction limited image. For a 5" scope, this occurs around F16 for the three colors of red, green and blue. However, the visual spectrum continues beyond blue to violet, and this will lie outside the Airy disc by a substantial margin. The attached image shows the Airy disc at high power from a 5" F16 achromat.
For shorter focal ratios, the red, green and blue colors will not be within the Airy disc, so some of each color will hang outside the image, depending on the focus position. I will post some shorter ones next.
For shorter focal ratios, the red, green and blue colors will not be within the Airy disc, so some of each color will hang outside the image, depending on the focus position. I will post some shorter ones next.
Attached Image:
