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Formula for determining Chromatic aberration in achromats and apochromats.?
I heard that if you square the diameter of a refractor in inches you can determin what focal ratio it would need to provide a color free image. This seems okay for a 3 inch (f9) or a 4 inch (f16) but a 2 inch could be an f4? a 6 inch would need f36? doesn't seem right.
Oh yeah and that supposed formula was for achromats. I really with they would let you Edit a question once you posted it
1 Answer
- GeoffGLv 77 years agoFavorite Answer
The formula I've usually seen is that the focal ratio for an achromat needs to be 5xD where D is the aperture in inches. Alternatively it can be expressed as D/5 where D is the aperture in mm.
