Quote:
Originally Posted by robz
I guess that there is a lot going for refractors that many of us ''mirror boys'' have bypassed in the aperature fever years.
I think my next purchase will be a 6 inch refractor?..........or bigger?  |
The low chromatic aberration of small refractors comes naturally due to their small aperture and typically long focal ratios. Refractors are inherently achromatic if their focal ratio is longer than aperture (in mm) * 0.122. That's why the 60mm Tasco (which is probably f/9 to f/11) showed no issues there.
A 6" refractor would have to be slower than f/18 (more than 2.7m focal length) to benefit from this criterion. I can just picture it…
Cheers
Steffen.