Clarification for: “Some of you may already be familiar with this effect with red dot sights, in the human eye its called ‘astigmatism’.

“this effect” meaning that blurry dot, starburst, multiple dots, elongated dot…etc… the dot is not clear and round.

Astigmatism is caused by an irregular shape of the cornea or lens in the eye. Its a distortion (i.e. irregular shape of the cornea or lens) that causes a failure to focus ‘light’ to the same point, refraction changes in different meridians of the eye, causing the eye to focus at different points and this is the reason you see dot sights with the dot being blurry, or starburst, or multiple dots, or elongated dots…etc.. In other words, astigmatism is a condition where parallel rays of light passing from the cornea do not converge to a point focus on the retina. Color is light in some wavelength. So basically, in the human eye ‘astigmatism’ is the parallel of chromatic aberration.

The ABBE value is a number given to describe the amount of chromatic aberration of an ophthalmic lens material, not its clarity.

The higher the number, the less amount of aberration, for example, High Index Glass has an ABBE value of 42 and Crown Glass has an ABBE value of 59.

Chromatic aberration is a lens distortion that causes a failure to focus all colors to the same point, instead causing them to focus at different points. It occurs due to the varying refractive index of lens materials for different wavelengths of light. Its also known as chromatic distortion, color aberration, color fringing, or purple fringing. Some of you may already be familiar with this effect with red dot sights, in the human eye its called ‘astigmatism’.