I ran across an idea for a fast achromat the other day that called for grey-tinted glass for the diverging lens. The idea was that in the middle where the glass is thin, there would be little attenuation, but out near the edges where you get into trouble with poorly focussed red and blue, less light would get through, and the result would be less light in the diffraction rings, more in the Airy disc--the apodization idea.
It ocurred to me then that an improved visual achromat could be made by using, not grey tint, but yellow-green. The thick and deeper-colored glass at the edges would attenuate red and blue where they do more harm than good, but the thin glass in the middle would transmit them. This would give a brighter, better-colored image than yellow-green or minus violet filters, which impose their color artifact on all of the light equally.
Batches of vat-dyed glass are used for color filters, but utility glass like that is likely not flint. Also, this glass would need to be lighter-toned than even the light yellow-green Wratten #11, which attenuates 78% over the visible spectrum, in the 1-2mm thickness used in typical filters. You'd want the color to get about as dark as a #11 at the edge. The performance could be helped if a lens could be designed and built with the flint as thin as possible at the center. And of course, you'd HAVE to call it an "apo".
So, light-benders, any merit in this, or should I go adjust my dosage?
Ron
It ocurred to me then that an improved visual achromat could be made by using, not grey tint, but yellow-green. The thick and deeper-colored glass at the edges would attenuate red and blue where they do more harm than good, but the thin glass in the middle would transmit them. This would give a brighter, better-colored image than yellow-green or minus violet filters, which impose their color artifact on all of the light equally.
Batches of vat-dyed glass are used for color filters, but utility glass like that is likely not flint. Also, this glass would need to be lighter-toned than even the light yellow-green Wratten #11, which attenuates 78% over the visible spectrum, in the 1-2mm thickness used in typical filters. You'd want the color to get about as dark as a #11 at the edge. The performance could be helped if a lens could be designed and built with the flint as thin as possible at the center. And of course, you'd HAVE to call it an "apo".
So, light-benders, any merit in this, or should I go adjust my dosage?
Ron
