A large aperture achromatic doublet
like the instrument employed by Greenacre and Barr is remarkably ill-suited for assessing any 'delicate' colour phenomena.
Tenders invited for Air spaced (mounted) achromatic doublet
Designated an official product of the International Year of Astronomy 2009, this compact 80-mm achromatic doublet
sports a 11/4-inch rack-and-pinion focuser with integrated T-thread adapter, and a mounting bar with 1/4-20 threaded holes to attach the scope to an included photo tripod.
Later research into this effect revealed a surprising result, that is, the high reduction of the chromatic aberration of a single plano-convex objective lens by placing an achromatic doublet
lens at some position along the focal length, and inside the prime focus itself.
The 6-inch objective is an achromatic doublet
, as is the 1 5/8-inch finder objective.