What is parallax, and why do you need its detuning in optical sights. Measuring shooting distance with parallax correction, or What is parallax? Favorite old games

Space is one of the most mysterious concepts in the world. If you look at the sky at night, you can see a myriad of stars. Yes, probably, each of us has heard that there are more stars in the Universe than grains of sand in the Sahara. And scientists from ancient times have been drawn to the night sky, trying to unravel the mysteries hidden behind this black void. Since ancient times, they have been improving methods for measuring cosmic distances and the properties of stellar matter (temperature, density, rotation speed). In this article, we will talk about what stellar parallax is and how it is used in astronomy and astrophysics.

The phenomenon of parallax is closely related to geometry, but before considering the geometric laws underlying this phenomenon, let's plunge into the history of astronomy and figure out who and when discovered this property of the movement of stars and was the first to put it into practice.

Story

Parallax as a phenomenon of changing the position of stars depending on the position of the observer has been known for a very long time. Even Galileo Galilei wrote about this in the distant Middle Ages. He only assumed that if a change in parallax could be seen for distant stars, this would be evidence that the Earth revolves around the Sun, and not vice versa. And it was absolutely true. However, Galileo could not prove this because of the insufficient sensitivity of the then equipment.

Closer to our days, in 1837, Vasily Yakovlevich Struve conducted a series of experiments to measure the annual parallax for the star Vega, which is part of the constellation Lyra. Later, these measurements were recognized as unreliable when, in the year following Struve's publication, 1838, Friedrich Wilhelm Bessel measured the annual parallax for the star 61 Cygnus. Therefore, no matter how sad it may be, the priority of discovering the annual parallax still belongs to Bessel.

Today, parallax is used as the main method for measuring distances to stars and, with sufficiently accurate measuring equipment, gives results with minimal error.

We should move on to geometry before looking directly at what the parallax method is. And to begin with, let's recall the very basics of this interesting, albeit unloved by many, science.

Fundamentals of Geometry

So, what we need to know from geometry to understand the phenomenon of parallax is how the values ​​of the angles between the sides of a triangle and their lengths are related.

Let's start by imagining a triangle. It has three connecting lines and three angles. And for each different triangle - their angles and lengths of the sides. You cannot change the size of one or two sides of a triangle with the same values ​​of the angles between them, this is one of the fundamental truths of geometry.

Imagine that we are faced with the task of finding out the value of the lengths of two sides, if we know only the length of the base and the values ​​of the angles adjacent to it. This is possible with the help of one mathematical formula that relates the values ​​of the lengths of the sides and the values ​​of the angles lying opposite them. So, let's imagine that we have three vertices (you can take a pencil and draw them) that form a triangle: A, B, C. They form three sides: AB, BC, CA. Opposite each of them lies an angle: angle BCA opposite AB, angle BAC opposite BC, angle ABC opposite CA.

The formula that links all these six quantities together looks like this:

AB / sin(BCA) = BC / sin(BAC) = CA / sin(ABC).

As we can see, everything is not quite simple. From somewhere we have a sine of angles. But how do we find this sine? We will talk about this below.

Fundamentals of trigonometry

The sine is a trigonometric function that determines the Y-coordinate of an angle built on the coordinate plane. To show this clearly, they usually draw a coordinate plane with two axes - OX and OY - and mark points 1 and -1 on each of them. These points are located at the same distance from the center of the plane, so a circle can be drawn through them. So, we got the so-called unit circle. Now let's build some segment with the origin at the origin and end at some point on our circle. The end of the segment, which lies on the circle, has certain coordinates on the axes OX and OY. And the values ​​of these coordinates will represent the cosine and sine, respectively.

We figured out what a sine is and how to find it. But in fact, this method is purely graphical and was created rather to understand the very essence of what trigonometric functions are. It can be effective for angles that do not have infinite rational values ​​of cosine and sine. For the latter, another method is more effective, which is based on the use of derivatives and binomial calculation. It is called the Taylor series. We will not consider this method because it is quite complicated to calculate in the mind. After all, fast computing is a job for computers that are built for it. The Taylor series is used in calculators to calculate many functions, including sine, cosine, logarithm, and so on.

All this is quite interesting and addictive, but it's time for us to move on and return to where we left off: on the problem of calculating the values ​​of the unknown sides of a triangle.

Sides of a triangle

So, back to our problem: we know two angles and the side of the triangle to which these angles are adjacent. We only need to know one corner and two sides. Finding the angle seems to be the easiest: after all, the sum of all three angles of a triangle is 180 degrees, which means that you can easily find the third angle by subtracting the values ​​of two known angles from 180 degrees. And knowing the values ​​​​of all three angles and one of the sides, you can find the lengths of the other two sides. You can test this yourself with any of the triangles.

And now let's finally talk about parallax as a way to measure the distance between stars.

Parallax

This, as we have already found out, is one of the simplest and most effective methods for measuring interstellar distances. Parallax is based on the position of a star depending on its distance. For example, by measuring the angle of the apparent position of a star at one point of the orbit, and then at the directly opposite one, we get a triangle in which the length of one side (the distance between opposite points of the orbit) and two angles are known. From here we can find the two remaining sides, each of which is equal to the distance from the star to our planet at different points in its orbit. This is the method by which the parallax of stars can be calculated. And not only stars. Parallax, the effect of which is actually very simple, despite this, is used in many of its variations in completely different areas.

In the following sections, we will take a closer look at the applications of parallax.

Space

We have talked about this more than once, because parallax is an exceptional invention of astronomers, designed to measure the distances to stars and other space objects. However, not everything is so clear-cut here. After all, parallax is a method that has its own variations. For example, there are daily, annual and secular parallaxes. One can guess that they all differ in the time interval that passes between the measurement stages. It cannot be said that an increase in the time interval increases the measurement accuracy, because each type of this method has its own goals, and the measurement accuracy depends only on the sensitivity of the equipment and the selected distance.

Daily parallax

Daily parallax, the distance with which is determined using the angle between the straight lines going to the star from two different points: the center of the Earth and a selected point on the Earth. Since we know the radius of our planet, it will not be difficult, using the angular parallax, to calculate the distance to the star using the mathematical method we described earlier. The main use of diurnal parallax is to measure nearby objects such as planets, dwarf planets, or asteroids. For larger ones use the following method.

annual parallax

Annual parallax is still the same method of measuring distances, with the only difference that it focuses on measuring the distances to stars. This is exactly the case of parallax that we considered in the example above. Parallax, which can be quite accurate in determining the distance to a star, must have one important feature: the distance from which the parallax is measured must be the greater the better. The annual parallax satisfies this condition: after all, the distance between the extreme points of the orbit is quite large.

Parallax, examples of methods of which we have considered, is certainly an important part of astronomy and serves as an indispensable tool in measuring the distances to stars. But in reality, today they use only a yearly parallax, since the daily parallax can be replaced by more advanced and faster echolocation.

Photo

Perhaps the most famous type of photographic parallax can be considered binocular parallax. You must have noticed it yourself. If you bring your finger to your eyes and close each eye in turn, you will notice that the angle of view of the object changes. The same thing happens when shooting close objects. Through the lens, we see the image from one angle of view, but in reality the photo will come out from a slightly different angle, since there is a difference in the distance between the lens and the viewfinder (the hole through which we look to take a photo).

Before we end this article, a few words about why such a phenomenon as optical parallax can be useful, and why it is worth learning more about it.

Why is it interesting?

For starters, parallax is a unique physical phenomenon that allows us to easily learn a lot about the world around us and even about what is hundreds of light years away: after all, with the help of this phenomenon, you can also calculate the size of stars.

As we have already seen, parallax is not such a distant phenomenon from us, it surrounds us everywhere, and with the help of it we see as it is. This is certainly interesting and exciting, and that is why it is worth paying attention to the parallax method, if only out of curiosity. Knowledge is never redundant.

Conclusion

So, we have analyzed what the essence of parallax is, why it is not necessary to have complex equipment to determine the distance to the stars, but only a telescope and knowledge of geometry, how it is used in our body and why it can be so important for us in everyday life. We hope the information provided was useful to you!

Due to the wide distribution among people close to shooting sports (a sniper is also an athlete) and hunting, a large number of various optical devices (binoculars, spotting scopes, telescopic and collimator sights), questions related to the quality of the image given by such devices, as well as the factors affecting the accuracy of aiming. Since we have more and more people with education and / or having access to the Internet, the majority still heard or saw such words related to this problem as PARALLAX, ABERRATION, DISTORTION, ASTIGMATISM, etc. somewhere. So what is it and is it really that scary?

Let's start with the concept of aberration.

Any real opto-mechanical device is a degraded version of an ideal device made by man from some materials, the model of which is calculated based on simple laws of geometric optics. So in an ideal device, each POINT of the object under consideration corresponds to a certain POINT of the image. In fact, this is not so. A dot 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 have to go in an ideal optical system, are called aberrations.

Aberrations are different. The most common types of aberrations in optical systems are 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).

Here is what is written about various types of aberrations in the most general form in a textbook for technical schools (not because I cite this source because I doubt the intellectual abilities of readers, but because the material is presented here in the most accessible, concise and competent way):

"Spherical aberration - manifests itself in the mismatch of the main foci for light rays that have passed through an axisymmetric system (lens, lens, 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 The correction of spherical aberration is carried out by selecting a certain combination of positive and negative lenses that have 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 something similar - E.K.).

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 in the image plane in two mutually perpendicular

directions, a complex asymmetric scattering spot, resembling a comma in appearance (comma, English - comma). In complex optical systems, coma is corrected in conjunction with spherical aberration by lens selection.

Astigmatism lies in the fact that the spherical surface of a light wave during the passage of the optical system can be deformed, 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 a certain distance from each other. from 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 due to the uneven curvature of the optical surface in different cross-sectional planes of the light beam incident on it. Astigmatism can be corrected by choosing lenses so that one compensates for the astigmatism of the other. Astigmatism (however, like any other aberrations) can also be possessed by the human eye.

Distortion is an aberration that manifests itself in the violation of the geometric similarity between the object and the image. It is due to the non-uniformity of the linear optical magnification in different parts of the image. Positive distortion (the increase in the center is less than at the edges) is called pincushion. Negative - barrel-shaped. The curvature of the image field lies in the fact that the image of a flat object is sharp not in a 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, with 1/R=<СУММА ПО i произведений fini>, where fi is the focal length of the i-th lens, ni is the refractive index of its material. In a complex optical system, the curvature of the field is corrected by combining lenses with surfaces of different curvature 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 with 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 .

Which of the above is important for a respected reader?

1. Spherical aberration, coma, astigmatism and chromatic aberration can have any serious effect on the accuracy of aiming in an optical sight. But, as a rule, self-respecting firms do everything in their power to correct these aberrations as much as possible. The criterion for correcting aberrations is the resolution limit of the optical system. It is measured in angular units, and the smaller it is (at equal magnification), the better the sight is corrected for aberrations.
2. Distortion does not affect the resolution of the sight and is manifested in some distortion of a sharply visible image. Many may have come across devices such as door peepholes and fisheye lenses, in which distortion is not specifically corrected. As a rule, distortion in optical sights is also corrected. But some presence of it in the sight, as will be said below, is sometimes very useful.

Now about the concept of parallax.

"Parallax is the apparent displacement of the observed object due to the movement of the shooter's eye in any direction; it appears as a result of a change in the angle at which the object was seen before the shooter's eye moved. As a result of the apparent displacement of the aiming pin or crosshair, an error in aiming is obtained, this The error is the so-called parallax.

To avoid parallax, when aiming with a telescope, one should accustom oneself to put the eye always in the same position with respect to the eyepiece, which is achieved by a butt stock and frequent aiming exercises. Modern weapons telescopes allow moving the eye along the optical axis of the eyepiece and away from it up to 4 mm without parallax aiming error.

V.E. Markevich 1883-1956
"Hunting and sporting firearms"

It was a quote from the classic. From the point of view of a man of the middle of the century, it is absolutely correct. But time goes by... In general, in optics, parallax is a phenomenon due to the fact that the same object is observed by one observer at different angles. So the determination of the range by optical rangefinders and artillery compass is based on parallax, the stereoscopicity of human vision is also based on parallax. The parallax of optical systems is due to the difference in the diameters of the exit pupil of the device (in modern sights 5-12 mm) and the human eye (1.5-8 mm depending on the background illumination). Parallax exists in any optical device, even the most corrected for aberration. Another thing is that parallax can be compensated by artificially introducing aberration (distortion) into the optics of the ocular part of the sight so that the total distortion of the sight is zero, and the distortion of the reticle image is such that it compensates for the parallax of the sight in the entire plane of the entrance pupil. But this compensation occurs only for the image of an object located at a distance of practical infinity of the sight (the value is given in the passport). That is why some professional scopes have a so-called. parallax adjustment device (Parallax Adjust-ment Knob, Ring, etc.) rough - focus on sharpness. In non-parallax corrected scopes, it is best to actually aim with the eye directly in the center of the scope's exit pupil.

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 around the entire exit pupil of the sight, observe the relative position of the image of the object and the sight reticle. If the relative position of the object and the grid 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 infinity point of view. The rest can use a sighting machine and any small object located at a distance of more than 300 meters.

In the same simple way, you can determine the presence or absence of parallax in collimator sights. These sights have no parallax - a big plus, since the aiming speed in such models increases significantly due to the use of the entire diameter of the optics.

From the above, the conclusion is:

Dear users of optical sights! Do not bother your head with such terms as astigmatism, distortion, chromatism, aberration, coma, etc. Let this remain the lot of opticians-designers and calculators. All you need to know about your scope is whether it's parallax corrected or not. Find out by following the simple experiment described in this article.

I wish everyone a positive outcome.

Egor K.
Revision September 30, 2000
Sniper's Notebook

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Parallax is the apparent movement of the target relative to the reticle as you move your head up and down when you look through the scope's eyepiece. This happens when the target does not hit on the same plane as the reticle. To eliminate parallax, some scopes have an adjustable lens or wheel on the side.

The shooter adjusts the front or side mechanism while looking at both the reticle and the target. When both the reticle and the target are in sharp focus, with the scope at its maximum magnification, the scope is said to be free of parallax. This is the definition of parallax from a shooting point of view, where most shots are fired at distances over 100 meters and the depth of field (DOF) is large.

Shooting airguns is another matter. When using a high magnification scope at relatively close range (up to 75 meters), the image will be out of focus (blurred) in any range other than the one it is currently set to. This means that in order to have an acceptable picture, the "objective" or side focus must be adjusted for each of the distances you wish to shoot.

A few years ago it was discovered that a side effect of parallax/focus correction was such that if the scope had sufficient (greater than 24x) magnification it could be used for typical airgun ranges, with a shallow depth of field this made accurate distance estimation possible. By marking the parallax adjustment wheel at the distances at which the image was in focus, which has now become a simple "correction / adjustment of parallax", field target received an elementary, but very accurate rangefinder.

Parallax Adjustment Types

There are 3 types: front (lens), side and rear. Back - focus is adjusted using a ring close in size and location to the zoom ring (zoom - approx.transl.). Rear focusing scopes are rare and none have found their way into field targeting to date, so they will not be considered further. What remains is front focus and side focus.

I) Adjustable lens (front focus)

It is relatively simple mechanically and generally less expensive than a side focusing mechanism. There are expensive exceptions such as the Leupold, Burris, Bausch&Lomb and these models are popular in field targets due to their exceptional optical qualities. However, there is an ergonomic disadvantage to using parallax on the lens and this is due to the fact that you have to reach for the front of the scope to adjust it while aiming.

This is a particular problem in standing and kneeling shooting. Some models, such as the Burris Signature, have a "resettable calibration ring". The Leupold line of scopes includes scopes where the lens does not rotate; the lens only moves when you use the knurled ring. In most front focus scopes, the entire front lens housing rotates.

It can be very difficult to rotate smoothly and may result in distance measurement becoming secondary as the scope was not designed with this feature in mind. Consequently, these are simpler sights that do not contain too many optical elements, so the possibility of possible errors and malfunctions is very low.

There are various tricks to make distance reading easier, such as some kind of collar around the lens or a prism to view the scale from the shooting position. The left-handed shooter may find this type of scope more comfortable than sidewheel scopes.

II) Side focus

Side-wheel scopes in field targeting are now the norm rather than the exception. Although usually expensive and limited in range, they offer one big advantage over front parallax models: ease of access to the side wheel instead of the front of the scope. The distance marks on the wheel can be read without acrobatic exercises, i.e. violation of the position.

The side wheels are generally easier to turn than the lens, hence finer adjustments are possible. However, this mechanism is much more vulnerable. If the wheel has play, you should always measure the distance in the same direction to compensate for this play.

Side wheel scopes are usually only supplied with a handle that is too small to accommodate the 1 yard and 5 yard scale steps needed for the field target. This little wheel works for its intended purpose - as a parallax correction device, not as a rangefinder.

Instead, a large wheel is installed on top of the existing one. Larger wheels are usually made of aluminum and are held in place with threaded studs or screws. The original handles are usually 20-30 mm in diameter. "Custom" wheels typically range in size from 3 to 6 inches in diameter.

It may also turn out that it is necessary to make a pointer on the wheel in order to replace the stock one. A thin piece of plastic or metal sandwiched between the upper and lower half rings and placed along the edge of the wheel should be sufficient.

You can see some really huge wheels around the world, but don't go bigger than 6-7 inches as it's more vulnerable and the resolution won't improve. You will have a large scale step, but the errors will be larger too. It is advisable to mount the tag on the scope itself (for example, using the third mount ring, or using an already existing pointer on the scope), rather than mounting something between the two rings of the scope bracket. So you don't have to calibrate the parallax again if you have a reason to take the scope off.

Calibrating "parallax adjustment" as a rangefinder

This is the most difficult part of the whole scope procedure. In the process, you can become frustrated and tired, and prolonged eye strain can be a waste of time and effort. During competition, everything you do in the process of shooting will be wasted if you don't mark the correct distance, so being careful with your parallax markings is sure to pay dividends.

You must have access to the 50m line, roulette and targets. It is especially important that you use the correct type of target to set up your course markings. Standard falling FT targets are the best because they will be your only source of information for estimating distances during competition. Take two of these targets and spray-paint one of them black and white - the kill zone. Paint the second one white and black for the kill zone.

Place the targets at a safe distance and shoot about ten times each. This will provide a contrast between the paint on the target and the gray metal of the target itself. Using nylon cord, tie a few large knots through the metal ring on the front panel. Separate loops and windings on the cord can be an invaluable help in solving the problem of precise focusing.

It may be necessary to wrap a piece of tape around the parallax adjustment wheel to provide a surface on which to write numbers. Pointed permanent markers are the best option for tape recording. Alternatively, sticker numbers can be used to mark directly on polished aluminium. Now is the time to decide which labeling method you will use.

It is an unfortunate fact that the greater the distance, the smaller the pitch between the marks, merging into one after 75 yards. The average distance between 20 and 25 yards on a 5" side wheel is about 25mm. Between 50 and 55 yards this decreases to about 5mm. Consequently, long ranges are the most difficult to determine and repeat. The 20 yard mark is a good place to start. This is above the scope's lower focus limit, but not far enough to be difficult.

Place both targets at exactly 20 yards from the front lens of the sight. It is important that the front lens is used as the reference point for all your measurements otherwise it may result in inaccurate distance readings. Do the following:

1. Focus your eye on the reticle first. Turn the wheel until the target is approximately in focus.
2. Repeat, but try to decrease the amount of wheel movement until the target image is clear and sharp.
3. Using stationery, make a tiny (!) mark on the wheel next to the "pointer".
4. By repeating steps 2 and 3, you are looking for marks that will be in the same place each time you take a measurement. If so, you can mark it with a number and make it your permanent value for that distance. If that's not possible and you do end up with a few marks, you can simply compromise between the extreme marks, or take as the operating point where they are densest and label the value.
5. Repeat steps 1-4 with the white target. The marks may be in the same place, but they may not be. Record the difference when going from black to white target. It is important to practice the rangefinder in various lighting conditions. This is important because the human eye will accommodate much faster if the image is highly detailed and fairly simple. As the wheel spins, your brain tries to correct the image from blurry to sharp a bit before it gets REALLY sharp. This difference depends on the lighting conditions, your age, current physical condition, etc. You can reduce this effect by always spinning the wheel at the same speed, not too fast, but not "millimeter by millimeter". The image will focus more definitely if you make larger movements, like 5-10 yards and not just 1-2 yards.

As noted earlier, the important thing is not to try too hard. As soon as you concentrate on the target, your own eyes will try to compensate for parallax errors and bring the target into focus while the crosshairs are out of focus (Fig. 1). You won't notice this until you stop looking at the target, at which point you will notice that the crosshair is sharp and the target is suddenly blurry and out of focus (Fig. 2).

That's why you should focus your eyes first on the crosshairs of the reticle and just take a little look at the target or just use your peripheral vision to observe the target while keeping while focusing on the crosshairs. In this way, the target will be seen sharply while the reticle also remains sharp (Figure 3).

Fig.1	Fig.2	Fig.3

After completing the 20-yard parallax adjustment, move 5 yards further. Repeat this procedure for every 5 yards from 20 to 55 yards, constantly checking other distances to make sure nothing has changed. If things start to change, take a break and try again.

After 20-50 yards have been completed, set short distances with the accuracy of your choice. As noted earlier, setting 17.5 yards for the 15 to 20 range and then stepping down 1 yard from 15 yards should be more than enough. When you reach the near range of your scope, check your tape measure. You may only have to move the target six inches to determine this distance. It might be 8.5 yards or something like that.

Most scopes used in the FT cannot measure distances from 8 yards, only from 10 or 15 yards. If you turn the zoom down, you will see these close targets more sharply, but never really clearly. A "focus adapter" can help this problem, but many shooters can live with it anyway. Regardless of the distance, set the elevation for that distance by shooting at one of the cardboard targets in the manner described earlier. Now you have a sight that will work as a rangefinder for all distances of the marked trajectory.

Now for the test. Need a friend or colleague. Ask them to set up several targets at various distances, each of which has been measured with a tape measure. They will have to record these distances. Then measure the distance to each of the targets, in turn telling the value of each to your friend. It will write the named values ​​next to the measured distances.

This is an interesting exercise because it validates your data in real life. At a pre-measured distance, your brain can deceive you because you know how far the target is. The test simulates competition conditions, because you have absolutely no way to know for sure the distance to the target, except for your scope. There is a saying in field targeting and it is very true: Trust Your Scope - Trust Your Scope.

* * * * * * * * * * * * * * * * * * * * * * * * *

If you have followed this guide up to this point, you have set up your rifle and scope and are capable of winning any competition. The rest, as they say, is up to you. Welcome to Field Target. Enjoy!

Parallax shift

Parallax shift is a well known phenomenon, more or less every scope suffers from it. The main reason for this is the change in temperature, but also on the height above sea level. Or some light filters may affect it. If we want to compare the behavior of different scopes due to rangefinder errors, it is always recommended to consider a rangefinding error of 55 yards at 10 degrees of temperature difference. This value was 0.5-4 yards on the scopes I tested.

There are several different ways to deal with parallax shift, from appropriate scale shift and slanted distance marks to multiple (or adjustable) pointers. But the point is that you have to recognize your scope and its rangefinder at different temperatures.

Unfortunately, there is only one way to find out about the necessary corrections: you have to test the scope at different times of the year and times of the day, placing targets every 5 yards and measuring them many times, very accurately. It is important that the riflescope remain in the shade and be outdoors for at least half an hour before taking measurements.

After a dozen experiments, you will see how your scope reacts to temperature. The parallax shift can be continuous with temperature changes, but it can't be "almost nothing and then all of a sudden a 'jump'". If you already know how your scope works, you will also know how much and how to compensate to get correct range results.

Isolating the scope is completely useless because it can only protect from direct sunlight, but it is still exposed to ambient heat and parallax shift will occur. Also, water cooling is not a good idea :-) We can do two things that are really useful: monitoring the ambient temperature, or even better if the scope itself (see picture below). And, of course, keep your sight in the shadows at all times. The shot only takes 2-3 minutes so the scope can't get too much heat and has 10-15 minutes to get back to air temperature.

BFTA Riflescope Mounting Instructions
- Updated Maestro

Knowing the distance between observation points D ( base) and offset 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 almost unshifted sun

Astronomy

Daily parallax

Daily parallax (geocentric parallax) - the difference in directions to the same luminary from the Earth's center of mass (geocentric direction) and from a 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 seen in the optical non-mirror viewfinder and the image obtained in the photograph. Parallax is almost imperceptible when photographing distant objects, and quite significant when photographing close objects. It arises due to the presence of a distance (basis) between the optical axes of the lens and the viewfinder. The parallax value is determined by the formula:

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

Viewfinder parallax (scope)

A special case is the parallax of the sight. 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 - the angle at which an object is seen during focusing with 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.

Temporal 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 the exposure does not occur simultaneously over the entire area of ​​the photosensitive element, but sequentially as the slit moves, then 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 it moves in the opposite direction, then it will be narrowed.

Story

Galileo Galilei suggested that if the Earth revolved around the Sun, then this could be seen from 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 Lyra), the results were published in 1837. However, scientifically reliable measurements of the annual parallax were first carried out by F. W. Bessel in 1838 for the star 61 Cygnus. The priority of discovering the annual parallax of stars is recognized by Bessel.

see also

Literature

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

Links

• The ABC's of Distances - An overview about measuring distances to astronomical objects.

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See what "Parallax" is in other dictionaries:

- (astro) the angle formed by visual lines directed at the same object from two differences. points. As soon as the parallax of the object and the distance between the two points from which this object was observed are known, then the distance of the object from ... ... Dictionary of foreign words of the Russian language

- (from Greek parallaxis deviation) 1) a visible change in the position of an object (body) due to the movement of the observer's eye. 2) In astronomy, a visible change in the position of a celestial body due to the movement of the observer. Distinguish between parallax, ... ... Big Encyclopedic Dictionary

parallax- apparent displacement of the object under consideration when changing the angle of its perception or moving the observation point. Dictionary of practical psychologist. Moscow: AST, Harvest. S. Yu. Golovin. 1998. parallax ... Great Psychological Encyclopedia

PARALLAX, the angular distance that a celestial object appears to be displaced relative to more distant objects when viewed from opposite ends of the base. Used to measure the distance to an object. Star parallax... ... Scientific and technical encyclopedic dictionary

PARALLAX, parallax, husband. (Greek parallaxis evasion) (astro). The angle that measures the apparent displacement of the luminary when the observer moves from one point in space to another. Daily parallax (the angle between the directions to the luminary from a given place ... Explanatory Dictionary of Ushakov

- (from the Greek parallaxis deviation) the apparent displacement of the object in question when the angle of its perception changes ... Psychological Dictionary

- (from the Greek parallaxis deviation) in aviation, astronautics, the lateral displacement of the plane of the final orbit of the aircraft relative to the starting point, usually measured along a great circle arc from the starting point of the aircraft to the track ... ... Encyclopedia of technology

- (from the Greek. parallaxis deviation) in astronomy, a change in the direction of the observer astro. object when the observation point is shifted equal to the angle under the eye from the center of the object, the distance between the two positions of the observation point is visible. Usually used P., ... ... Physical Encyclopedia

Exist., Number of synonyms: 1 offset (44) ASIS Synonym Dictionary. V.N. Trishin. 2013 ... Synonym dictionary

parallax- Apparent change in the position of an object in relation to another object when the viewpoint changes... Geography Dictionary

Parallax(Parallax, Gr. change, alternation) is the change in the apparent position of the object in relation to the distant background, depending on the location of the observer. Primarily this term was used for natural phenomena, in astronomy and geodesy. For example, such a displacement of the sun relative to the column when reflected in water is parallax in nature.

Parallax effect or parallax scrolling in web design is a special technique where the background image in perspective moves slower than the foreground elements. This technology is used more and more often, as it looks really impressive and cool.

This effect of three-dimensional space is achieved with the help of several layers that overlap each other and move at different speeds when scrolling. Using this technology, you can create not only an artificial three-dimensional effect, you can apply it to icons, images and other page elements.

Disadvantages of the parallax effect

The main disadvantage of parallax These are website performance issues. Everything looks beautiful and stylish, but the use of javascript / jQuery , with the help of which the parallax effect is created, greatly makes the page heavier and greatly reduces its loading speed. This is because it is based on complex calculations: javascript has to control the position of each pixel on the screen. In some cases, the situation is further complicated by cross-browser and cross-platform problems. Many developers recommend using the parallax effect on a maximum of two page elements.

Alternative Solution

With the advent of CSS 3, the task has become a bit easier. With it, you can create a very similar effect, which will be much more economical in terms of resource costs. The bottom line is that the content of the site is placed on one page, and moving through subpages occurs using the CSS 3-transition method. This is the same parallax, but with a slight difference: the fact is that it is impossible to achieve that the movement is carried out at different speeds using only CSS 3. In addition, this standard is not supported by all modern browsers. Therefore, there are difficulties here as well.

Conclusion

Although the parallax effect is popular, not everyone is in a hurry to use it when creating a site due to the above problems. Apparently, it just takes time for technology to be able to overcome the difficulties that have arisen. In the meantime, this option can be used on one-page sites: this way it will definitely be remembered and will be able to keep the user.

parallax in javascript

• jQuery-parallax scrolling effect - a plugin that binds the parallax effect to the movement of the mouse wheel
• scroll deck- plugin for creating a parallax effect
• jParallax- turns page elements into absolutely positioned layers moving according to the mouse