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"Showing a system with chromatic difference of spherical aberration. O" ₌ image of O for red light; O'" for blue. The system is under—corrected for red, and over—corrected for blue rays." —Encyclopaedia Britannica, 1910

Light Correction of Blue and Red Lights using Spherical Lens

"Showing a system with chromatic difference of spherical aberration. O" ₌ image of O for red light;…

"O' is the virtual image of O formed at a spherical surface of centre C and radius CS." —Encyclopaedia Britannica, 1910

Virtual Image Formed on Spherical Surface

"O' is the virtual image of O formed at a spherical surface of centre C and radius CS." —Encyclopaedia…