Newton reflex telescope


Produces the first reflection telescope from Newton to today, more than 300 years have passed, and people have added other designs, producing a lot of deformation. For example, in a set of lenses in a Newtonian telescope, a Schmidt-Newton is produced, in addition to this, there are many modifications, but their basic structures are Newton.

Today, some of the most famous telescopes in the world are European structures. For example, the Hale astronomical telescope in the Baile Mountain Observatory, the main mirror is 5 meters; the Keck astronomical telescope of the WM Kah Observatory, its main mirror is spliced ​​from 36 hexagonal mirror, which combines 10 meters in diameter. Mirror; there is also an Hubble space telescope and a Newtonian telescope.

The optical system of the calibrated mirror of the "Newton-type reflected telescope optical axis is used: the optical axis of the objective lens and the eyepiece optical axis. The main mirror (objective) optical axis is parallel to the axis of the main mirror, passes through a vice mirror (small plane mirror); the eyepiece optical axis is perpendicular to the main mirror axis, and also passed through a secondary mirror. When the two optical axes are passed through the same point, and the two axes are completely coincident after the secondary mirror is reflected, that is, a optical axis, the optical axis is adjusted.

Calibration of the optical axis of the Newton-type reflected telescope

When lacking the inspection instrument, it can be judged by the actual observation to adjust whether the optical axis is adjusted. Find a sunny night having a good atmospheric static, take a star with the highest magnification of the telescope (the number of main mirrors indicated by millimeters) (if there is no equatorial instrument, you can watch the Northern Star). Put the star point in the center of the eyepiece (to reduce the aberration brought by the eyepiece), carefully adjust the focus, adjust the focus from the focus, then adjust to the focus.

Whether the star appears in the focus, it is very thin, very sharp, whether the diffraction rings after defocus is concentric circle, which reflect the image quality of the telescope. If you can see a few circle diffraction rings after defocus, but perfect, there are some "burrs" evenly around, which means that the accuracy of the mirror surface is slightly poor, but the optical axis is adjusted or good. If the rocked star point turns a small fan shape, and move the star icon in the eyepiece field, the divergence direction of the sector does not change, which means that the optical axis of the telescope needs to be adjusted.

optical axis adjustment step and the auxiliary tool optical axis adjustment can be performed as follows:

Optical axis adjustment step and auxiliary tool

Adjustive mirror focus, Allows it perpendicular to the main mirror axis

to adjust the secondary mirror

to adjust the secondary mirror, which is located directly below the eyepiece.

Regulating the secondary mirror, making the eyepiece optical axis Reflectively reflect the main mirror center

to adjust the main mirror, and the optical axis is coincided with the eyepiece optical axis

The above is just a substantially method of the optical axis, there will be some problems during the specific operation, sometimes it is difficult to control accuracy. Here, several auxiliary tools are introduced:

with double cross pipe:

tube outer diameter goggles interface diameter, one end of the tube, the center of the cover The 2mm diameter round hole, the other end of the tube pulls the double cross zone with white cotton line, and the two-wire spacing is 3 ~ 4mm. The tube length is determined by the following method: from the mirror focus cartridge into the peeking tube (peeping), one end of the peep hole is equal to the outer end of the eyepiece, and the double cross-cross line is approximately 20 to 30 mm from the secondary lens.

Make peeking tube is not limited (if you use a 31.7mm eyepiece interface, consider making it in the black box of Kodak film), the key is to be stable after inserting the mirror focus. Can't shake too much. Double cross lines are to be pulled, and the small squares of the intersection and the linkage of the peephole should be the axis of the eyepiece.

Main mirror center positioning point: cut a black paper with a diameter of 5mm, accurately stick to the center of the objective lens with two sides. (Because the central area of ​​the primary mirror does not participate in the imaging, this black spot will not have a negative impact)

The main lens opening is at the cross line

at the main mirror opening The thick line pulls the cross line, requires two lines perpendicular to each other, and intersects the main mirror axis. (Pull the cross line on the main mirror opening may affect the operation of the vice mirror, so it is best to mark the four intersection points of the cross line and the lens barrel. When you think that the cross is taken, you can take it first, if necessary Re-pull again.)

These three tools are not complicated, but you will soon find them very useful. With them, now we can start adjusting the light axis of the telescope step by step.

0. Pre-tester pointing to

Remove the secondary mirror, adjust the bolts behind the main lens until the cross, cross line intersection, the center of the objective lens When the cross-line intersection is a straight line formed in the objective lens, it indicates that the main mirror is strikingly correct. (The next step is to adjust the main lens, pre-plus this step can make the following operations easier.)

Adjust the program mirror focus, make it perpendicular to the main mirror

< P> In the eyepiece, it is observed from the peephole, and it can be seen from the lobent hole to the double cross line (the eyelimeter is the axis of the axis), which will be extended with the main mirror wall. At some point, this point is marked, and the position is measured with a ruler, then refer to the position of the mirror focus on the lens barrel, we can determine whether the mirror focus is vertical with the main mirror.

Adjust the secondary mirror, enabling it on the main mirror axis

to remove the peeking tube, install the secondary mirror, and substantially adjust the secondary mirror, so that the eye can be in the eye of the eye. The image of the main mirror formed by the vice mirror is seen, and it should also be possible to see the cross wire at the cross wire and the main mirror opening. From these images, we can see the relative position of the secondary mirror and the cross line, if the center of the vice mirror is coincident, indicating that the secondary mirror is on the main mirror axis, otherwise it needs to be adjusted.

Adjust the vice mirror, enabling it under the direction of the eyepiece, focusing on the direction of the mirror, and the secondary mirror is obviously located below the focus, but after this Seeing accuracy and cannot be guaranteed. At this time, the peeking, the eye is seen from the peephole, the outermost ring is the inner wall of the peeking tube (the double cross line does not work now, and the middle is the secondary mirror. The outer circular profile of the secondary mirror and the inner wall of the peeking tube are in concentric circles, and the description will be met, otherwise the secondary mirror is adjusted in the main mirror axis direction. (If the light is too small, the light is too dark, it can be made on the inner wall of the main mirror in which the peeking is correct; if the peeking tube is too thin, the outer circular profile of the adjovir, The peeking tube can be pumped or shortened.)

Regulating the secondary mirror pointing, making the eyepiece optical axis reflecting the primary mirror center: On the previous step, the side is peeable The hole is observed, one side regulating the secondary mirror, until the main mirror is in the outer circular profile of the image formed in the secondary mirror, and the outer circular profile of the secondary lens is concentric.

Adjust the main mirror to point to the optical axis and the eyepiece optical axis

with the flashlight to illuminate the double cross pipe, the eye looks in from the snorkeling, and you can see the double The image of the cross line, the center point of the main mirror, and the image of the double cross-reflection. Adjust the bolts behind the main mirror so that the above three are concentric. At this point, the optical axis of the mirror is completed.

In the above adjustment steps, according to the different design of the secondary mirror bracket, the next operation will bring more or less influence on the results of the previous step, so it can return the previous operation if necessary, may There are several times, and finally you can get satisfactory results. For the first time, I have regulated some work, once adjusted, as long as the secondary mirror branch is stable, the future work is much easier, even if it is transported, it will render the main mirror, generally need to adjust the bolt after the main lens, take the help The telescope can be adjusted to the optimal state soon.

Supplementary Description

Generally speaking the intersection of the optical axis with the adjunctional mirror at the center of the secondary mirror. This can be considered in the telescope of the long-focus distance, but in a large diameter, the short focal of the Newton reflective telescope, the dimension of the secondary mirror is also large, and the distance between the two ends of the secondary lens is no longer approximately considered. The optical axis intersects the B point of the secondary mirror, not the A point where the secondary mirror center is located. This is equivalent to a displacement from the central position to the main mirror direction and the direction away from the eyepiece. The displacement amount in these two directions can be calculated using the following formula:

displacement = secondary mirror short edge length / (4 * primary mirror ratio)

, for example, a telescope 35mm long, the main mirror ratio is 5, then the displacement amount in both directions is 1.75 mm.

If there is a telescope with such a short focal distance, this situation needs to be taken into account. Calculating the displacement, in the second step of the above step, the secondary mirror should be left slightly away from the eyepiece; in the third step, we see the outer circular profile of the secondary mirror and the inner wall of the peeking tube are circular, In fact, the secondary mirror has been displaced in the direction of the main mirror, and no additional adjustment is required.

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