Aberrations in the lenses
Mostly we find real lenses behave differently from their design through thin lens equations, which leads to the presence of aberrations, as the aberration is a distortion in the image, and it also varies according to the lens size, thickness, material, and object position, in addition to that The most common type of aberration is chromatic aberration, which has to do with color.
As the index of refraction of the lenses is dependence on wavelength or color, and also images are produced in different places with magnifications and colors, which means the independence of the law of reflection from wavelength, and therefore this problem does not occur in mirrors, and this is another advantage of mirrors in optical systems such as telescopes .
Types of aberration in lenses
If the camera lenses create exactly what we see, then they will be in an ideal condition, while the physics is not so easy, as we often find optical aberrations, which become some defects that appear in the images, and in the following are the types of aberrations that may occur in the lenses :
chromatic aberration
Chromatic aberration is one of the easiest and most popular ways to identify a group, also known as fringing, as it is a name derived from the technique of aligning colors around broad subject lines, and they appear frequently in sensitive lenses, becoming noticeable in high-contrast images.
Chromatic aberration is the failure of color wavelengths to reach the correct focal plane, as well as each wavelength with its own refractive index alone, in addition to the fact that when they pass through glass they do not meet in the place necessary for them, and it is worth noting that chromatic aberration is divided into two types: :
- Longitudinal: which has an effect on the whole image, and becomes more difficult with high-speed numbers.
- Lateral: which is based on the effect on the angles, and this is done when all the colors focus on the same plane, while the focus becomes far from the optical axis.
- On the other hand, lens designers work to reduce chromatic aberration through special coatings such as fluorite.
zombie apocalypse
The people most familiar with comas are those who have taken a lot of night photography, as modern lens design still poses a problem, although there are a group of lenses that are better than others in this area.
The word (coma) is also taken from the Latin language, where it denotes a cloud of dust that surrounds the nucleus of a comet, as this optical phenomenon occurs as a result of the entry of points of light outside the axis to reach the lens, which distorts it, thus creating the illusion of the photographer with the presence of tails.
It may appear as a flicker or slowly fall through the image frame, and it is worth noting that city lights and fireworks are the most likely to appear like this when photographing, in addition to that, this problem can be avoided by using lenses with aspherical elements.
spherical aberration
Spherical aberration problems are now less than ever, as modern lens design has discovered ways to reduce the defects of spherical lenses , whereby the lens, when shaped like a ball, refracts light rays as they pass in varying amounts in the center against the edges.
Thus, the convergence ends at different points through the optical axis, and the unique shape that it is made of leads to the disappearance of the refractive error, so that all the rays meet correctly at one focal point.
Astigmatism
Astigmatism, also known as a condition that occurs to some people in their eye, as they know what is happening in it, and it is the entry of a ray of light into the lens on a vertical or horizontal plane, causing an ellipse instead of an ordered focal point, Which leads to a blurry illusion in directions.
Astigmatism can be detected by looking at the vertical and horizontal lines in any image, especially in the edges area. If there is strange movement blur, whether in the vertical or horizontal direction, then the lens has an aberration, and if the fog is severe, this means that the lens has It distorts significantly, but in this case it can be reduced by using a smaller aperture.
Types of optical aberration
Aberrations are defined as visual irregularities, which are defects in the eye that cause light to be unable to pass through the retina in an effective manner, and also lead to defects in the visual image . 3]
Low-order aberrations
It is one of the most common causes of vision problems, as it represents approximately 85% of visual aberration cases, and includes the following cases:
- Myopia: This happens when the eye is very long, and the cornea becomes bulging outward, making the vision clear to nearby objects, while it becomes distorted or blurred to distant objects.
- Farsightedness: This is the exact opposite of myopia, and is often known as (farsightedness), and patients with hyperopia have shorter eyeballs and flattened corneas, which leads to seeing objects at a far easier distance than those at a distance Close.
- Astigmatism: or what is known as the condition (astigmatism), and it occurs when the corneas take the shape of a football instead of the circular shape, which is the normal shape, and vision in this case becomes blurred and blurry at different distances, and people with astigmatism have proportions Different, but lead to some problems with daily activities, in addition to the fact that this condition can occur with long-sightedness or myopia.
Higher-order aberrations
These aberrations are higher-resolution or specific abnormalities in the structure of the eye, and can occur as a result of abnormalities of scar tissue, the eye, disease, traumatic injury, complications of surgery, or serious eye conditions such as cataracts, as well as there are more than 60 types of Higher order aberrations. In general, some symptoms may appear with these conditions, such as:
- Contrast issues.
- Double vision ( Dyplopia).
- starburst
- Limited night vision.
- auras;
- Blurred eyesight.
In addition, these conditions do not occur often, so they are difficult to diagnose and treat, and it is worth noting that these patients may suffer from higher order aberrations with lower order aberrations at the same time, which makes them suffer greatly