Parallax - what is it? Parallax and aberrations of optical sights Parallax with reference to the cursor

home Parallax - a phenomenon detected when observing the surrounding space, consisting in a visible change in the position of some fixed objects relative to others located on different distances from each other as the observer's eye moves. We encounter the phenomenon of parallax at every step. For example, looking out of the window of a moving train, we notice that the landscape seems to rotate around a distant center in the direction reverse movement

Parallax in sights is the discrepancy between the plane of the target image formed by the lens and the plane of the sighting reticle. Tilting the reticle causes parallax at the edges of the field of view. This is called oblique parallax. The absence of a flat target image in the sight over the entire field of view, due to poor-quality manufacturing of the lenses and sight assembly, or due to significant aberrations of the optical system, causes “irremovable parallax.” Typically, a sight is made in such a way that the image of a target 100-200 m distant is projected by the lens into the plane where the aiming reticle is located. In this case, the parallax range seems to be halved between distant and near targets. As the target approaches the shooter, its image also moves closer to the shooter (in an optical system, the target and its image move in the same direction). Thus, in the general case, a sight is characterized by a mismatch between the target image and the reticle. When the eye moves perpendicular to the axis of the sight, the target image moves in most cases in the same direction relative to the center of the reticle. The target seems to “move” away from the aiming point; when tilting or shaking the head, it “darts” around the aiming point. In addition, the reticle and the target are not clearly visible at the same time, which worsens the comfort of aiming and minimizes the main advantage of a telescopic sight over a conventional one. Because of this, a sight without focusing on the shooting distance (without a parallax elimination device) allows for a highly accurate shot only at one specific distance. A high-quality scope with a magnification greater than 4x must have a device to eliminate parallax. Without this, it is quite difficult to find and keep the eye in the desired position, on the line connecting the aiming mark and the point on the target; the reticle is generally not in the center of the field of view. A slight movement of the reticle along with the target image can be detected when shaking the head, especially when the eye moves from the calculated position of the exit pupil, which is explained by the presence of distortion in the sight eyepiece. This can only be eliminated in scopes that have a parabolic lens in the eyepiece. Focusing a sight is the operation of setting the image produced by the lens in a given plane - the plane of the aiming reticle. The relationship between the longitudinal shift of the focusing lens and the amount of image displacement is determined by calculation. Typically, scopes either move the entire lens or an internal component located near the reticle. A scale indicating the focusing distance in meters is applied to the lens frame of the sight. By moving the lens to the desired division (firing distance), you eliminate parallax. A sight containing a focusing device is, of course, a more high-quality and complex product, since the moving lens must maintain its position in space relative to its own axis, that is, keep the line of sight unchanged. This centering of the lens focusing component relative to the geometric axis of the lens tube is achieved by maintaining tight manufacturing tolerances of the focusing component.

trains. Near objects move out of the field of view faster than distant objects, which is why the landscape appears to be rotating. If objects lie in the same plane, then parallax will disappear, there will be no different movements of objects relative to each other when the eye moves.

How do you know if your scope is parallax corrected or not? Very simple. It is necessary to point the center of the sight reticle at an object located at infinity, fix the sight, and, moving the eye along the entire exit pupil of the sight, observe the relative position of the object image and the sight reticle. If the relative position of the object and the reticle does not change, then you are very lucky - the sight is corrected for parallax. People with access to laboratory optical equipment can use an optical bench and a laboratory collimator to create an infinitely distant point of view. The rest can use a sighting machine and any small object located at a distance of more than 300 meters. The same simple method can be used to determine the presence or absence of parallax in collimator sights. The absence of parallax in these sights is a big plus, since the aiming speed in such models increases significantly due to the use of the entire diameter of the optics. Due to the wide spread among people close to shooting sports (a sniper is also an athlete) and hunting, a large number of different optical instruments (binoculars, spotting scopes, telescopic and collimator sights

) questions increasingly began to arise related to the quality of the image provided by such devices, as well as about the factors affecting the accuracy of aiming. Let's start with the concept. Any real optical-mechanical device is a degraded version of an ideal device, manufactured by man from some materials, the model of which is calculated based on the simple laws of geometric optics. Thus, in an ideal device, each point of the object under consideration corresponds to a certain point in the image. In fact, this is not so. A point is never represented by a dot. Errors or errors in images in an optical system caused by deviations of the beam from the direction in which it would go in an ideal optical system are called aberrations. There are different types of aberrations. Most common the following types aberrations of optical systems: spherical aberration, coma, astigmatism And distortion. Aberrations also include the curvature of the image field and chromatic aberration (associated with the dependence of the refractive index of the optical medium on the wavelength of light).

Spherical aberration - manifests itself in the mismatch of the main foci for light rays passing through an axisymmetric system (lens, objective, etc.) at different distances from the optical axis of the system. Due to spherical aberration, the image of a luminous point does not look like a point, but a circle with a bright core and a halo weakening towards the periphery. Correction of spherical aberration is carried out by selecting certain combination positive and negative lenses having the same aberrations, but with different signs. Spherical aberration can be corrected in a single lens using aspherical refractive surfaces (instead of a sphere, for example, the surface of a paraboloid of revolution or something similar).

Coma. The curvature of the surface of optical systems, in addition to spherical aberration, also causes another error - coma. Rays coming from an object point lying outside the optical axis of the system form a complex asymmetric scattering spot in the image plane in two mutually perpendicular directions, resembling a comma in appearance (comma, English - comma). In complex optical systems, coma is corrected together with spherical aberration by selecting lenses.

Astigmatism lies in the fact that the spherical surface of a light wave can be deformed when passing through an optical system, and then the image of a point that does not lie on the main optical axis of the system is no longer a point, but two mutually perpendicular lines located on different planes at some distance from each other friend. Images of a point in sections intermediate between these planes have the form of ellipses, one of them has the shape of a circle. Astigmatism is caused by the uneven curvature of the optical surface in different cross-sectional planes of the light beam incident on it. Astigmatism can be corrected by selecting lenses so that one compensates for the astigmatism of the other. Astigmatism (as well as any other aberrations) can also occur in the human eye.

Distortion is an aberration that manifests itself in a violation of the geometric similarity between the object and the image. It is due to the uneven linear optical magnification in different areas of the image. Positive distortion (the increase in the center is less than at the edges) is called pincushion distortion. Negative - barrel-shaped.
The curvature of the image field is that the image of a flat object is sharp not in the plane, but on a curved surface. If the lenses included in the system can be considered thin, and the system is corrected for astigmatism, then the image of the plane perpendicular to the optical axis of the system is a sphere of radius R, and 1/R=, where fi- focal length of the i-th lens, ni is the refractive index of its material. In a complex optical system, field curvature is corrected by combining lenses with surfaces of different curvatures so that the value of 1/R is zero. Chromatic aberration is caused by the dependence of the refractive index of transparent media on the wavelength of light (light dispersion). As a result of its manifestation, the image of an object illuminated by white light becomes colored. To reduce chromatic aberration in optical systems, parts with different dispersion are used, which leads to mutual compensation of this aberration..." (c) 1987, A.M. Morozov, I.V. Kononov, " Optical instruments", M., VSh, 1987

παραλλάξ , from παραλλαγή , “change, alternation”) - a change in the visible position of an object relative to a distant background depending on the position of the observer.

Knowing the distance between observation points D ( base) and the displacement angle α in radians, you can determine the distance to the object:

For small angles:

The reflection of the lantern in the water is significantly shifted relative to the practically unchanged sun

Astronomy

Daily parallax

Daily parallax (geocentric parallax) - the difference in directions to the same body from the center of mass of the Earth (geocentric direction) and from given point on the Earth's surface (topocentric direction).

Due to the rotation of the Earth around its axis, the position of the observer changes cyclically. For an observer located at the equator, the parallax base is equal to the radius of the Earth and is 6371 km.

Parallax in photography

Viewfinder parallax

Viewfinder parallax is the discrepancy between the image visible in an optical non-mirror viewfinder and the image obtained in the photograph. Parallax is almost unnoticeable when photographing distant objects, but is quite significant when photographing close objects. It arises due to the presence of a distance (basis) between the optical axes of the lens and viewfinder. The parallax value is determined by the formula:

,

where is the distance (basis) between the optical axes of the lens and viewfinder; - focal length of the camera lens; - distance to the aiming plane (subject of shooting).

Viewfinder parallax (sight)

A special case is sight parallax. Parallax is not the height of the sight axis above the barrel axis, but the error in the distance between the shooter and the target.

Optical parallax

Rangefinder parallax

Rangefinder parallax is the angle at which an object is visible when focusing using an optical rangefinder.

Stereoscopic parallax

Stereoscopic parallax is the angle at which an object is viewed with both eyes or when photographed with a stereoscopic camera.

Time parallax

Temporal parallax is a distortion of the shape of an object by parallax that occurs when shooting with a camera with a curtain shutter. Since exposure does not occur simultaneously over the entire area of ​​the photosensitive element, but sequentially as the slit moves, when shooting fast moving objects their shape may be distorted. For example, if an object moves in the same direction as the shutter slit, its image will be stretched, and if in the opposite direction, it will be narrowed.

Story

Galileo Galilei suggested that if the Earth revolved around the Sun, this would be noticeable by the variability of parallax for distant stars.

The first successful attempts to observe the annual parallax of stars were made by V. Ya. Struve for the star Vega (α Lyrae), the results were published in 1837. However, scientifically reliable measurements of the annual parallax were first carried out by F.V. Bessel in 1838 for the star 61 Cygni. The priority of the discovery of the annual parallax of stars is recognized by Bessel.

see also

Literature

  • Yashtold-Govorko V. A. Photography and processing. Photography, formulas, terms, recipes. Ed. 4th, abbr. - M.: “Art”, 1977.

Links

  • The ABC's of Distances - a review of measuring distances to astronomical objects.

Wikimedia Foundation.

2010.:

Synonyms

Parallax (from the Greek παραλλάξ, from παραλλαγή, “change, alternation”) -

— change in the apparent position of an object relative to a distant background depending on the position of the observer.

Parallax is used in geodesy and astronomy to measure the distance to distant objects. Based on the phenomenon of parallax binocular vision. Also from the word parallax comes the non-systemic unit of distance measurement known to many from science fiction, and not only films, the parsec.

The name comes from allax arcsecond pairs and denotes the distance to an object whose annual parallax is equal to one arcsecond (for example, a parsec is 3.26 light years or 30.85 trillion kilometers!).

So why is it necessary to adjust parallax on an optical sight?

But why? The optical system of the sight is designed in such a way that the image of a distant target is projected by the lens into the plane where the aiming reticle is located. Parallax in sights is the discrepancy between the plane of the target image formed by the lens and the plane of the aiming reticle. This can be either the front focal plane of the lens (FFP) or the rear focal plane of the eyepiece (SFP). The nature of parallax is a change in the so-called solid angle when the distance to the target changes. If the target is brought closer, the angle increases and thereby increases the rear segment of the lens, spreading the focal plane of the lens and the reticle into different parallel planes. This is what causes parallax! And if the parallax is not adjusted, it will introduce an error when shooting depending on the position of the shooter’s eye relative to the axis of the sight!

You can notice parallax in the following way: if the sight has an aiming reticle in the focal plane of the lens, then when the eye moves perpendicular to the axis of the sight, you can notice that the target image ‘floats’ relative to the center of the reticle and the aiming point seems to ‘move’ away from the target.

In most modern sights, the reticle is located in the rear focal plane of the eyepiece, and in such sights, parallax is manifested by the blurring of the aiming reticle and the inability to see simultaneously and with equal clarity the image of the target and the aiming reticle, if the target is not at an infinitely distant distance.

In order to simultaneously see the image of the target and the aiming reticle with equally high clarity at an infinitely distant distance, you need to make adjustments to the settings of the optical system of the sight for each specific firing range, changing the interfocal distance of the lens and eyepiece.

To eliminate parallax in sights, there is a lens focusing mechanism that allows you to place the image from the lens exactly in the plane of the aiming reticle.

Typically, this is done by moving the entire lens system of the lens or just the inner part.

There are two types of parallax adjustment devices - AO (AdjustableObjective) and SF (SideFocusing).

With AO, the parallax adjustment ring is located directly on the scope lens. A scale indicating the focusing distance is applied to the lens barrel.

Parallax is eliminated by rotating the ring on the lens and thus adjusting the lens to the desired shooting distance. This method is more common due to its ease of implementation and low cost. The disadvantage of this method is the inability to turn the parallax adjustment ring while not in the shooting position.

With SF, the parallax adjustment mechanism is located on the side of the scope and is sometimes equipped with a large removable wheel for convenient and smooth parallax adjustment.

In motion, parallax means a change in the location of an object against some background relative to an observer who is in place. This term has gained popularity on the Internet. In particular, a website with dynamic elements in its design looks interesting. Parallax is a way of designing a page on the Internet, used by webmasters to attract a large number of visitors.

What is parallax like?

Parallax scrolling can be used vertically as well as in a straight line. The best example is Nintendo. Many of us remember with nostalgia computer games, represented by the movement of the main characters from the left side of the screen to the right. It is also possible to move downwards along a vertical straight line. often used on the web. To create a vertical slider, you can use JavaScript or CSS 3.

They are characterized by the described three-dimensional spatial effect. The game creators used several background layers. They differ in texture, and movement occurs at different speeds.

Don't think that parallax is only about creating a 3D effect. You can move existing icons on the page. Moreover, it looks quite attractive. A particularly good option is to use an individual trajectory for each of them. In this case, different icons are used, moving along different trajectories. This design attracts attention.

Picture coming to life

It's hard to find a site without images. High-quality and demonstrative drawings attract visitors. But the most attention is drawn to various kinds of dynamic images. Indeed, if there is movement when visiting a site, it attracts attention. The likelihood of a resource visitor returning to a dynamic image increases significantly. Did it seem like it was moving or not? Therefore, to attract visitors to the site, it is worth studying such a concept as the parallax effect.

Examples of sites with moving images:

  • hvorostovsky.com;
  • www.kagisointeractive.com.

As shown in the examples, the perception is improved by a menu that drops down into sub-items. This element saves time for visitors and is therefore attractive to them.

jQuery library

The term jQueryParallax defines the library of the same name. Thanks to it, it is easy to achieve the effect of movement in 3D format. In the jQuery library, a three-dimensional perception is created different ways. One of them is to move background objects horizontally at the same time at different speeds. This library is characterized by the presence of a large number of different kinds of properties. And the displacement described here represents only a small part of its capabilities.

The site looks quite attractive, for the creation of which various modern elements were used. One of them is parallax. Example sites might look like this:

  • www.grabandgo.pt;
  • www.fishy.com.br;
  • www.noleath.com;
  • buysellwebsite.com.

jParallax is represented by layers that move with mouse movement. Dynamic elements are characterized by absolute ;). Each of them is characterized by its own size and movement at an individual speed. This can be text or an image (at the request of the resource creators).

Site visitor perception

After this, a person usually pays attention to the fact that the page is designed efficiently, conveniently and competently. This fact usually commands respect. Sometimes curiosity arises to try other elements. Available on the Internet great amount identical sites. How to make your resource special?

If you like the design, the visitor will stay for a longer period. Thus, the likelihood that he will be attracted by the posted information increases and he will show interest. As a result, the person will take advantage of the service, product or promotional offer offered.

Favorite old games

The concept of “parallax” should be familiar to all fans of consoles of the 80s and 90s. This applies to games:

  1. Mario Bros.
  2. Mortal Kombat.
  3. Streets of Rage.
  4. Moon Patrol.
  5. Turtles in Time.

That is, parallax is a technique that has been used for a fairly long period. These games are indeed remembered with some nostalgia. After all, they seem to be imbued with the character of that period.

The images on the screen are created using a technique called parallax scrolling. It is not surprising that this technique has gained well-deserved popularity. This design concept is quite warmly perceived by those who played in the 80-90s or watched their friends’ leisure time.

Parallax scrolling

Marketers of the world's leading brands have long been using various kinds of technical advances. Thus, it becomes possible to interest even a casual site visitor.

Parallax scrolling was used quite successfully by Nike. The company's original website was developed by designers Weiden and Kennedy. But this design was not preserved. The resource was gradually updated in accordance with modern trends. Activatedrinks.com is an example of a site whose design is reminiscent of the design used by Nike marketers from this period.

There shouldn't be too much dynamics

Do not forget that the design of the site is often key criterion, which guides the visitor. A poorly executed resource usually leaves the user with the impression that the owner company is not serious. But a website with various kinds of attractive design elements indicates the desire of the organization’s owners to interest visitors.

Here it is worth remembering about parallax. This is a wonderful tool. But even they shouldn’t get too carried away. Because the page on which there is a large number of various kinds of moving elements, quite difficult to understand. It is best to make the design moderately stylish and understandable.

Individual elements that require highlighting should be dynamic. There may also be a drawing that is created using layers moving relative to one another. Do not forget that a custom website is designed primarily for visitors. It should not be a masterpiece of a webmaster who has invested all his knowledge. After all, such an approach will only complicate perception.

How to create a movement on the site

How to make parallax? This question interests many website creators. It is not necessary to know the intricacies of writing tags. It is very convenient to use special resources on the Internet. From large number Available proposals include the following assistants:

  1. Plax is a program that is quite easy to use. It tends to give the page movement by moving the mouse.
  2. jQuery Parallax Image Slider - jQuery plugin used to create image sliders.
  3. Jquery Image Parallax - suitable for designing transparent pictures. Through his use of PNG, GIFs gain depth while being brought to life by movement.
  4. Curtain.js is used to create a page equipped with fixed panels. In this case, the effect of opening the curtains is observed.
  5. Scrolling Parallax: A jQuery Plugin is to create a parallax effect when scrolling the mouse wheel.

Some more useful plugins

As you know, information has the greatest value. And what large quantity ways to achieve what you want is known, the closer the probability of obtaining the correct result. Useful plugins used to create dynamics:

  1. jQuery Scroll Path - used to place objects on a specified path.
  2. Scrollorama is a jQuery plugin. It is used as a tool for attractive design of the material. Thanks to convenient scrolling, it allows you to “revive” the text on the page.
  3. Scrolldeck is a jQuery plugin. It is an excellent solution used as a presentation for websites designed as one page.
  4. jParallax renders layers to move based on mouse pointer movement.
  5. Stellar.js is a plugin with which any element is designed with the addition of a parallax scrolling effect.

Parallax with cursor snapping

This parallax looks quite impressive. Objects on a site page that seem motionless at first glance move when approached. It seems to come to life and follow the element being moved.

First you should stop at the drawing. The required image is placed in a frame, and its edges must be hidden. The method is very simple, and the resulting drawing looks quite attractive.

The parallax effect for a website is a wonderful design method. Its use indicates that due care was given to the creation of the resource. Therefore, it is worth paying attention to the services offered or information to read. Such sites look more advantageous against the background of identical, but simply designed resources.



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