As far as the optical and chemical properties of different glasses, I am a newbie, so please be kind in responding to this post.
We've all seen "ED" doublets that are branded "APO" or "Semi-APO" (e.g., Meade's ED line or the new Orion 80mm ED). We've also all seen high quality "conventional crown and flint" achromatic doublets (e.g., D&G, Alvan Clarke, Vixen, Carton, etc.).
While ED doublets are rarely true APOs at the commonly offered focal lengths (f5 through f7), I have to believe that if manufactured at equivalent quality at a more conventional f/10 through f/15 focal length, these ED doublets would be superior in color correction and therefore resolution (because all visible light comes to focuse at the same point) to to the high quality conventional crown and flint doublets. At longer focal lengths, wouldn't they approach true APOs at least in the 5-6 inch O.D. flavors?
Now the questions: Are modern glasses very much more expensive than conventional materials? If so, for comparison how much more expensive (i.e. 20%? 200%?) Are modern glasses harder to work with and figure accurately?
I for one would love to buy a D&G quality "ED" doublet. Especially if it was 6" and multi-coated.
I wonder if Barry at D&G or even Roland at A-P would consider a "co-op" order where 20-30 buyers subsidized the materials for ED doublets through advance payment and commissioned them to create ED "apo-achromats."
Feedback encouraged!
We've all seen "ED" doublets that are branded "APO" or "Semi-APO" (e.g., Meade's ED line or the new Orion 80mm ED). We've also all seen high quality "conventional crown and flint" achromatic doublets (e.g., D&G, Alvan Clarke, Vixen, Carton, etc.).
While ED doublets are rarely true APOs at the commonly offered focal lengths (f5 through f7), I have to believe that if manufactured at equivalent quality at a more conventional f/10 through f/15 focal length, these ED doublets would be superior in color correction and therefore resolution (because all visible light comes to focuse at the same point) to to the high quality conventional crown and flint doublets. At longer focal lengths, wouldn't they approach true APOs at least in the 5-6 inch O.D. flavors?
Now the questions: Are modern glasses very much more expensive than conventional materials? If so, for comparison how much more expensive (i.e. 20%? 200%?) Are modern glasses harder to work with and figure accurately?
I for one would love to buy a D&G quality "ED" doublet. Especially if it was 6" and multi-coated.
I wonder if Barry at D&G or even Roland at A-P would consider a "co-op" order where 20-30 buyers subsidized the materials for ED doublets through advance payment and commissioned them to create ED "apo-achromats." Feedback encouraged!
