求助：光轴

C8,晚上对着2公里外的光源调衍射圈，200倍、400倍下为什么看到的都是铜钱一样，根本看不到人家说的一层层的衍射圈，请大虾指点！

First step

The first step consists in observing a bright star (magnitude 0 or 1) at a magnification of about the diameter of the telescope in millimeters (ex.: 200x for a 200 mm). When the star is strongly defocused (figures below), it appears as a donut, the central hole being the shadow of the secondary mirror. This shadow must be perfectly centred (left figure). If it is shifted (right figure), it is necessary to have an effect on the collimation screw(s) situated in the direction of the shift (it may be useful to think with clock hours). If a star diagonal is in place, do not forget to take the up-down reversal of the image into account. if your arm is long enough, you can also put a finger in front of the aperture of the telescope and see the position where it corresponds to the shift.

请问右边的衍射圈，是否属于光轴不正比较严重？

不相信牧夫中就没有这方面的高手了！

右面的是光轴不正，好的办法是只稍微DEFOCUS， 留1，2个环，要明显得多。

折返镜的衍射环不像折射镜那么明显，所以做出一两个比较亮的环就可以了，做得越多越不明显～稍微离一点焦就可以了！

不愧是成都巽风，一语中地！谢谢老大了。

再请问一下:地面的光源可以么？其实在200倍左右，我几乎都能看出来灯的样子，是不是这样不行阿？

汗～～都能看出样子了，那是不行的……最好是对称的小圆点且越小越小

星点是不错的选择，当然也有其它办法在室内完成，论坛里有相应的介绍，可以搜索一下。

哈哈，我明白了。

看了一个英文的介绍，SCt调光轴的，就是上面的那段英文。好像这只是第一步，干脆我把有关步骤粘铁上来吧

First step
The first step consists in observing a bright star (magnitude 0 or 1) at a magnification of about the diameter of the telescope in millimeters (ex.: 200x for a 200 mm). When the star is strongly defocused (figures below), it appears as a donut, the central hole being the shadow of the secondary mirror. This shadow must be perfectly centred (left figure). If it is shifted (right figure), it is necessary to have an effect on the collimation screw(s) situated in the direction of the shift (it may be useful to think with clock hours). If a star diagonal is in place, do not forget to take the up-down reversal of the image into account. if your arm is long enough, you can also put a finger in front of the aperture of the telescope and see the position where it corresponds to the shift.

Only a very misaligned telescope (like can be a telescope which is never collimated) needs this rough alignment. If collimation is regularly checked, no asymmetry usually appears at this step.


Second step
The second step needs a dimmer star (magnitude 2 to 3) high above the horizon to minimize the effects of the atmospheric turbulence, and a higher magnification: 2 to 3 times the diameter of the telescope in mm (ex.: 500x for 200 mm). Do not hesitate to enlarge the image as much as possible, collimation defects are better visible. The star is slightly defocused back and forth (intra-focal and extra-focal patterns). A complex system of rings and central bright point appear (figures below).This system must open and close itself in a perfectly concentric and symmetrical manner and the bright point must be at the center of the rings (upper series). If it is not the case (lower series), the screws situated on the side of the asymmetry must be touched, like at the first step.
intra-focal        focus        extra-focal


It must be noticed that the misalignment presented above would not have been visible at the first step.



Third step
Final alignment is made in the same conditions as the previous step, but this time the star is carefully focused. The famous Airy pattern appears: a false disk surrounded by diffraction rings of decreasing brightness (figures below). If collimation is good (figure A), the first diffraction ring around the disk is complete and uniform. If this ring is not uniform (figure B), or if it is incomplete (figures C and D), one must adjust very slightly the collimation screws as in the previous steps.

Fig. A         
Fig. B         
Fig. C         
Fig. D
From one figure to the next, the angle of misalignment of the mirror has been doubled. The worst misalignment (fig. D) represents only a fraction of turn of a collimation screw of a SCT. On this type of instrument, the transition from fig. A to fig. B represents less than 1/20th of a turn, a modification of the orientation of the optical tube can be sufficient to produce this effect. It is evident that the precision of alignment increases with each step.
Unlike the previous steps which can tolerate a mediocre seeing, this last step needs good conditions of turbulence. Anyway, if no Airy pattern can be discerned, no high resolution result can be expected (except in big telescopes for whom the Airy pattern is rarely or even never visible).
A good way of familiarizing oneself with Airy patterns is to strongly diaphragm the telescope (at 50 mm for example) and to observe a star at a magnification of 100 to 150x. However, it is out of question to collimate the telescope with the diaphragm in place !

第一步first step最后有这么一句话：Only a very misaligned telescope (like can be a telescope which is never collimated) needs this rough alignment. If collimation is regularly checked, no asymmetry usually appears at this step.

是不是应该这么解释：只有不准的望远镜（就像从来没有调过的）才需要这样的粗调。如果经常检查和调整，通常不会出现这种不对称性。

是否可以这样理解，假如不是同心圆，那就是偏得相当厉害了；如果是同心圆，并不代表光轴是准确的。（图片仍然是第二楼的图片）

http://www.astronomy.com.cn/bbs/ ... highlight=%E7%82%B9

Because of a lack of information, few reflectors users dare to align their optics. Aditionally, the ones who venture to do it generally stop at the centering of the shadow of the secondary mirror on a much defocused star. This step is indeed necessary, on a very misaligned reflector, but it is not sufficient because of its inaccuracies. After this step, planetary images can still lose more than 50 % of their contrast.

翻译：
因为没有相关信息，很少有人敢于调整光轴，即使有敢于冒险的，也就是把中央反射镜的影子调整在中央即停止了。这一步确实很重要，对一个光轴偏移非常严重的望远镜来说。但是这是非常不够的，因为他不精确。通过这种调整，行星画面的反差仍然要丢失50％以上。”

这个帖子值得一看：
http://www.astronomy.com.cn/bbs/ ... D%E5%B0%84%E7%8E%AF

谢谢老兄的耐心指导！

看了一下上面的帖子，好深奥阿。

http://legault.club.fr/collim.html

把这篇文章的地质留下来

看路燈應該效果沒那麽好，你看看天狼星試試看。

今天晚上试验了一下，在阳台上用AUTOSTAR+840K，因为视宁度不好，而且无法对极轴，对这天狼星看了一个多小时都没敢下手。无奈还是找了一个2-3公里外的一盏明亮的灯用衍射圈调整了一下，感觉比较同心了。后来又看了2等星（不知道叫啥名），衍射圈在400倍下同心很好，800倍下晃动太厉害，看不出来。不过调整后，星点比以前实多了，地面估计至少5公里以外的一个洗浴中心的霓虹灯可以看清楚名字，性能个人感觉比从前至少提高了30％。心情很爽。