What is Chromatic Aberration?
The eye cannot simultaneously focus on the three regions of the spectrum where the cone-pigment absorptions peak since refraction at the cornea and lens is greater for short wavelengths than it is for long wavelength. Thus, it is said that the eye is not corrected for chromatic aberration. The medium- and long-wavelength peaks are quite close together and therefore the lens optimally focusses light of about 560 nm on the retina. Since the short-wavelength cones receive a slightly blurred image it is not necessary to provide the same spatial resolution that is provided by the other two sets of cones. The retina contains approximately 40 long-wavelength cones and 20 medium-wavelength cones for every single short-wavelength cone. The rods and cones are not evenly distributed on the retina. The central part of the retina, the fovea, contains only cones whereas at greater eccentricities there is a greater preponderance of rods. In the fovea the cones are densely packed and it is this part o
Answer provided by Brian Koch. Photo by Gene Tatroe. Chromatic aberration is a distortion caused by a lens that does not focus all of the different light colors to the same point. This is due to the lens having different refractive indices for the different light wavelengths: Figure 1: Chromatic aberration occurs when different wavelengths do not focus at a single point. Sometimes this is referred to as “purple fringing.” However, not all purple fringing is the result of chromatic aberration, sometimes it is due to sensor problems in digital cameras. Figure 2 shows areas in a photograph where chromatic aberration is evident: Figure 2: Example photograph that shows chromatic aberration. To reduce the effects of chromatic aberration, several different pieces of glass with varying refractive indexes are used.
Binoculars can suffer from a number of aberrations but this one is often discussed. Chromatic Aberration (CA) is the result of the various wavelengths of light not reaching focus at the same precise point in the image. CA is a function of refraction. Light from different wavelengths is refracted differently. Blue, yellow and red wavelengths of light reach focus at slightly different points along the focal length axis of the lens. The most important thing the user should understand is that it is impossible to completely eliminate CA from a lens system. It can be reduced, but cannot be eliminated altogether. There is longitudinal CA and Lateral CA. In an astro binocular, CA appears prominently in less than 1% of the objects viewed. So it might be considered one of the least critical aberrations on which to base a decision, unless of course you are buying your binoculars just to look at the moon. My advice is judge your choice of binocular on all the features that make a difference in the
