Chromatic aberrations in human language are color distortions that add to the original images of various kinds of parasitic distortions.
If you are an amateur, and somewhere you heard that some kind of lens gives you strong XA (chromatic aberrations, that’s how they are often called out for shortening), and then they looked at the photo for a long time and didn’t see anything – don’t be upset. In our time, the struggle over HA is in full swing. Now, in high-quality optics, it is very well possible to fight HA, and therefore it is really difficult to notice them.
There are axial, spherical, transverse and other types, but they all boil down to a distortion of the picture.
The main essence of chromatic aberration comes from dispersion, in other words, when a white beam expands into its spectrum, this is due to the fact that rays with different wavelengths (of different colors) are refracted at different angles, passing through the objective lens. It is enough to recall a lesson in physics with the refraction of rays in a prism, and a lens is two prisms connected by bases. It turns out puff picture. Often XA add different color spots and stripes, this is especially pronounced at the transition of contrasting subjects, often cite the example of trees.
Below is a picture filled with aberrations.
Of course, there are a number of lenses (namely, lenses give XA), which still suffer greatly from this ailment. But as they say: the optimists invent the plane, the pessimists – the parachute, because with the XA you need to fight to get high-quality pictures.
Very often XA pronounced in the area of unsharpness. In the people, aberrations, usually in the unsharp zone, are called freezing (‘Purple fringing’). Transitions in the area before the zone of sharpness are colored in purple (magenta) color, and beyond the area of sharpness in green. This is clearly seen in the example above. Many lenses have aberrations in the unsharp zone.
Spherical aberrations are the blurring of the boundaries between the contrasting elements in the zone of sharpness in the photo. The example above, a white shirt model smoothly flows into a dark background, erasing the border. Spherical aberrations are heavily affected by monocles. More details in the monocle section.
Sometimes confused purple and red halos in the photo with HA. Halos are simply parasitic highlights from a bright source in the frame. An example of such highlights is shown above.
How to be? How to treat this lens?
In modern lenses try to use low-dispersed elements. Nikon stands for ED (Extra-Low Dispersion – super small dispersion). These elements give less refraction for rays with different wavelengths (for rays of different colors).
Also now began to use aspherical lenses that allow you to get the final image with a smaller amount of XA.
In modern advanced cameras, there is an automatic control of aberrations — I don’t know how modern cameras do it (most likely with special algorithms), but they get rid of aberrations with a bang.
I also recommend simply remembering that aberrations appear when there are very contrasting elements in the frame (sun and sky, trees and sky, dark and light areas), when photographing a really strongly contrasting element, just remember that the photo will need to be modified if HA appear.
Most of the XA appears on the open aperture when used on wide-angle and high-aperture lenses, because the XA are visible on almost all cheap and mid-range lenses with a fully open aperture (under certain conditions).
Telephoto lenses have the most XA on the long end (maximum permissible focal length).
It is very easy (but not entirely correct) to get rid of HA – this is to make a photo black and white.
If it is necessary to completely get rid of XA during direct photography, then mirror-lens lenses, in which they are completely absent, will help in this, MS-11 1000mm F10.0 can serve as an example of such a lens.