详细讲解:如何调整牛顿反射式望远镜

天文一年级

原文请看:
http://skyandtelescope.com/howto/scopes/article_787_1.asp

如何调整牛顿反射镜：How To Collimate Your Newtonian ReflectorBy Nils Olof Carlin

Suppose you have bought a fine guitar with a lovely sound and are learning to play it. But after a while, you notice that it has gone slightly out of tune. What do you do? Learn how to tune it, or trade it in for a piano?

设想你买了一吧好吉他，音色不错，开始学习弹奏它。很快你发现吉他有点走调，该怎么办呢，是学习调整还是退换成一架钢琴？

Your Newtonian reflector will give great images of stars and planets — but only as long as you keep it well tuned. The "tuning" of a telescope is known as collimation. You may have heard that it is incomprehensible, tedious, time-consuming, a pain in the neck, and best avoided. I hope to convince you that it is none of these things. You can master it and in only a minute or two get your instrument ready for a star performance.

你的牛顿反射镜将把恒星、行星的优异像质呈现在你眼前，前提是只要你能把它调校到位。调校望远镜的光轴有个术语叫做Collimation。你以前可能听说过，这个过程是费解的，困难的，费时费力，腰酸背疼，最好能够避免。我希望使你相信，绝对不是这样的。你完全能够在很短时间内掌握它，使你的器材发挥到极致。

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If you aren't already acquainted with the optical parts of your telescope, now is the time. Here are the components that you will be lining up:

如果你还没有认识望远镜的各个部分，现在就来看看。以下是各个零部件：

The primary mirror. This is the paraboloidal mirror at the bottom of the tube. It has an aluminized surface that reflects starlight to form an image at the focal plane.

主镜。是位于镜筒底部的一块抛物面镜。表面镀铝膜，将星光反射到焦平面上成像。

The important thing to know that it has an axis of symmetry — the optical axis. On this axis, at the focal point, is a "sweet spot" where images of stars and planets are as sharp and crisp as they can be. Outside the sweet spot, an aberration known as coma visibly degrades the image. Coma makes stars appear asymmetric even if the telescope is perfectly focused — the farther the star is from the center of the focal plane, the worse it gets. In particular, this aberration can dramatically reduce the clarity of planetary detail.

重点是知道主镜有一个对称轴——光轴。在光轴上的焦点处有一个点，叫做“甜点（sweet spot）”，星星在此处成像既锐利又清晰，非常逼真。在“甜点”区域以外，成像的质量就下降，也就是常说的像差，慧差。当望远镜已经调好了，如果有慧差存在的话，星星所成的像就不对称了——距离焦平面越远越不对称。令人不可接受的是像差使行星表面的细节和清晰度大大下降。

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Surprisingly, the size of the "sweet spot" depends only on the main mirror's focal ratio (the mirror's focal length divided by its diameter) and not its size. For instance, even a perfect f/4.5 mirror, small or large, can provide "diffraction limited" performance only within a 2-millimeter (0.08-inch) circle at the focal plane. An f/10 paraboloid's sweet spot, by contrast, spans 22 mm (0.87 inch). (For the mathematically inclinded, the sweet spot's diameter is proportional to the cube of the f/ratio.)

另人意外的是，“甜点”的大小依赖于主镜的焦比（镜面的焦距与直径之比）而不是它的口径。举例来说，即使是f/4.5的镜子，不论尺寸大小，衍射的极限在焦平面只有不超过2毫米（0.08英寸）的光环。一个f/10的抛物面镜的甜点，扩展到22mm。从数学计算看，甜点的直径与f/焦比的立方成正比。

he primary mirror is held in an adjustable cell designed to support the mirror without deforming it. By adjusting the cell's collimation screws we can fine-tune the mirror's tilt and accurately position the sweet spot where we want it.

主镜放入一个可调节的支撑室内。通过调节支撑螺丝能改变镜面的斜度，使焦点在光轴上。

Because the sweet spot can be very small, this is by far the most critical part of collimation. Have a look at your telescope and make sure you know where these adjustment screws are and how they work.

因为甜点很小，这是调校光轴的关键。看一下你的望远镜调整螺丝在什么位置，如何工作的。

To make collimation easy, the center of the mirror should be marked in some way. I recommend marking it with a piece of electrician's tape. Don't make it too small — a ½-inch-diameter (or even slightly larger) spot works well.

为使调校过程简便，镜子的中央应该标记出来。我推荐使用电工黑胶布。直径不要太小，直径有半英寸（1.25厘米）或稍微大些的点就行。

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As long as it is smaller than your diagonal mirror, it will not affect your telescope's performance. If you plan to use a laser collimator, make a hole in the center of your spot. (Another approach is to use an adhesive binder reinforcement ring, the kind used by generations of school children to keep their homework from flying out of their 3-ring binders.)

只要它比斜面镜小一些就行，黑胶布也不会影响望远镜的性能。如果你打算使用激光校准仪，（另外一个办法是使用一个活页夹的夹子。）

The secondary mirror. This is a small, flat mirror that serves to move the image formed by the primary to the side of the tube, where it is viewed with an eyepiece.

副镜，是小的平面镜，它把主镜成的像反射到镜筒的旁边，用目镜看到。

To minimize harmful diffraction effects, the secondary, or diagonal, mirror is generally only large enough to let the central portion of the focal plane receive light from the whole primary mirror. You should center this fully illuminated area in the eyepiece by positioning the secondary in the correct location.

为减小不利的衍射效应，副镜，或平面镜的大小只是刚够把主镜在焦平面的像反射就行了。你应该调整副镜的位置，直到在目镜里看到的明亮的区域位于中央。

The secondary is attached to an adjustable holder suspended on a spider — often a cross made from thin sheet metal. Identify the adjustment screws for the secondary holder and the spider.

副镜安装在可调节的支架上——通常是十字交叉的薄金属支架。必要时调整副镜的支架螺丝。

The eyepiece. The third optical component in the telescope system is the eyepiece. It is a complex magnifying lens used to view the image formed at the focal plane. Like the primary mirror, the eyepiece has an optical axis, and this axis should be aimed at the center of the main mirror for best performance — though in practice it is the center axis of the focuser drawtube that you aim at the primary mirror.

目镜。是第三个部件。它是比较复杂的放大影像的透镜，观察焦平面的图象。目镜和主镜一样也有光轴，光轴应该对准主镜的中心——尽管实际上，目镜的光轴对准的是调焦筒（相当于调焦座）的中心。

A good eyepiece will render a sharp image in the central parts of the field of view (its sweet spot), but toward the edge not even the best and most expensive eyepieces can produce a perfect image. For this reason it is important to make sure that the sweet spots of the primary mirror and the eyepiece match up — the ultimate goal of collimation.

好的目镜在视场中央成像锐利，但在目镜的边缘即使最好和最昂贵的目镜成像也不行。所以使目镜和主镜的像吻合是调校光轴的终极目标。

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Now that you know what you're dealing with, look into the empty focuser and try to identify the optical parts just described. This is best done during daylight, with the telescope aimed at the ceiling or the sky (be careful to avoid the Sun).

现在你已经知道在干什么了，看一下空的调焦座认识一下提到的各个部分。白天做这项工作最佳，对着天花板和天空，（不要对着太阳）。

The illustration to the right shows what you should see: the secondary mirror in its holder, its elliptical face tilted 45° and appearing circular.副镜在支架中，椭圆斜面呈45度。

With your eye close to the focuser, you can see the primary mirror reflected in the secondary, and the secondary and its spider in turn reflected in the primary. Finally, inside this reflection of the secondary, you can see the focuser drawtube and your eye.

把眼睛靠近调焦座，你会看见副镜中有主镜的反射像，而副镜和它的支架也在主镜中有反射像。最后，在副镜的反射像中，你能看到调焦座的伸缩管和你的眼睛的像。

天文一年级

Once you are acquainted with the telescope's optical parts and what they look like in the focuser, you're ready to proceed. To get your telescope well collimated, here is what you need to accomplish:

一旦你认识了望远镜的光学部件并且在调焦座中的像，你就可以往下进行。以下就是要进行的步骤：·  

Step 1: Center the secondary mirror on the axis of the focuser drawtube.

1．把副镜中央置于调焦伸缩管的中轴。·  

Step 2: Aim the eyepiece at the center of the primary mirror.

2.把目镜中轴调整到主镜的中央。·  

Step 3: Center your primary mirror's sweet spot in the eyepiece's field of view.
3.把主镜的甜点调整到目镜视场中。

In most cases, only the last of these three steps will need to be repeated regularly; the first two are more or less set-and-forget operations. Now let's get to the nuts and bolts of actually collimating your reflector.

在绝大多数情况下，第3步是需要定期做的。前两步基本上被忽略了。现在让我们调整主镜的螺丝吧。

Step 1: Begin by making sure that the focuser and the secondary are lined up. The simplest and best tool for this step is a sight tube. (Read our sidebar for more on this collimation tool and others.) You slide it into the focuser, as you would an eyepiece, and look through the tube's peephole at the secondary. (If the secondary is far out of adjustment, you should first tilt and/or rotate it to get the reflection of the spot on the primary roughly centered in the sight tube before you proceed.) It may be difficult to distinguish the edge of the secondary from the reflected edge of the main mirror, so place a piece of white cardboard between the secondary mirror and the primary, as shown here.

最简单的工具是一个“sight tube”（注解，一个专用工具，可以从Orion买到）你把它放入调焦座，正象你把目镜放入一样，通过镜筒观测孔看副镜。（如果副镜位置不当，你应首先调副镜，使主镜的反射像位于副镜中央。）区分副镜的边缘与主镜的反射像有点难，所以在副镜和主镜之间放一个白纸卡片，象图中那样。

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The elliptical secondary should appear round and well centered in the circular opening of the sight tube. If it is, Step 1 is done. If not, either the secondary holder or the focuser (or both) needs attention.

椭圆形的副镜应看上去边缘是圆的，在光管开口处呈现环状。如果是这样的话，第1步完成了。如果不是这样，要么副镜支架或调焦座（或两者）需要注意了。

Try adjusting the secondary holder first. You can usually move it toward or away from the primary by adjusting the center bolt that joins the holder to the spider.

先调整副镜的支架。一般调整支架中央的螺栓使副镜朝向主镜或远离主镜。

If the error is toward either side of the sight tube (90° to the optical axis), also check to find out if the secondary is well centered in the telescope tube. If it isn't, adjust the spider's mounting screws until it is. If this checks out fine, then tilt the focuser by putting shims under its mounting plate.

如果偏差是朝着光管两边（与光轴成90度），也要检查副镜是否居于望远镜镜筒中央。如果不是，调整支架固定螺丝直到调正。如果这一步调好，然后倾斜调焦座，把shims放到接口板上。

Step 2: Here you adjust the tilt of the secondary mirror to aim the focuser's axis at the center of the primary. First, remove the cardboard from the spider. Now, while viewing through the sight tube, carefully adjust the screws that tilt and rotate the secondary until the primary mirror's reflection appears centered in your field of view.

现在你已经调整了副镜的倾斜程度，把调焦座的中轴已经对准了主镜。首先，拿走挡在支架上的白纸片。现在，当你向sight tube(专用调镜工具)中看时，小心调整副镜的螺丝直到主镜的反射像出现在你视野的中央。

If your sight tube has cross hairs, align the primary's center spot with them; otherwise, center the outer edge of the primary within the sight tube. (Make sure that the sight tube is racked in far enough to let you see the whole primary mirror.) A laser collimator is even better for this step — just center the laser beam on the primary's center spot.

如果你的sight tube有“十字丝”的话，把主镜的中央点对准它；如果没有的话，把主镜的反射像的外周调到目镜筒中央。（确保sight tube的距离足够远，使你能看到整个主镜。）激光校准器做这一步工作更好——只要把激光束照射到主镜的中点上就行了。

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A small error in secondary alignment is usually not a problem. As long as the pointing error is no more than 1 or 2 percent of the main mirror's diameter, it makes no visible difference. However, if you plan to use a laser collimator in Step 3, you should be aware that even a tiny misadjustment here will throw off the final collimation.

副镜稍微有些偏离也问题不大。只要误差在主镜直径的百分之一或二以内，目视是觉察不到的。然而，如果你计划在第3步中继续使用激光校准器的话，你就要仔细调整了，否则差之毫厘，谬以千里。

If you have a truss-tube telescope, you will need to repeat Step 2 each time you reassemble the scope. With a solid-tube reflector, you need only check this once in a while.

如果你的望远镜镜筒是木架子组装起来的，你在每次组装好镜筒之后都需要重复步骤2的工作。如果你的镜筒是整体化的，你只用隔一段时间检查一次就行了。

Step 3: In this, the final and most critical step, you need to tilt the main mirror to center its sweet spot (and its optical axis) in the focuser. This procedure should be done at the beginning of each observing session and checked occasionally during the night, since temperature changes or routine handling may cause your telescope's components to shift enough to change collimation.

第3步，最后也是最关键的一步。你必须调整主镜的倾斜角度，使主镜的甜点（Sweet spot）处于调焦座的中央，光轴也要正。这项工作应该在每次观测之前检查，最好在夜间进行，因为温度的变化会导致各个部件的位置发生改变，影响调校的效果。

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The best tool for this procedure is a Cheshire eyepiece. Put it in the focuser and observe the reflection of its shiny 45°-angle face in the primary. By turning the primary's adjustment screws you can move this reflection until it appears centered on the primary mirror's center spot. If you can make these adjustments while looking in the Cheshire, so much the better; otherwise an assistant can be very helpful.

最好的工具是采用Cheshire目镜。把它放到调焦座上，观察它的45度角的反射面。拧动主镜的调整螺丝直到看到主镜的中央点。如果你能在Cheshire目镜中看到这个过程，那真是太好了，否则，在你眼睛盯着目镜时，你需要一个帮手去调整主镜的螺丝。

Most mirror cells have three adjustment screws or three pairs of push-pull adjustments. For simplicity's sake, I recommend using only two of the adjustments — the third one (which might as well be the one that is hardest to reach) can be left alone unless you run out of adjustment on one of the others.

绝大多数的镜室（固定支撑主镜）有3个调整螺丝或3对推拉杆。为简单起见，我推荐使用其中的两个——第3个保持原位不动，除非你已经调过另外两个螺丝，仍然无法使它居中时再调整第3个螺丝。

When Step 3 is done, the optical axis is accurately centered in the focuser, and collimation is complete. However, if you look carefully you will notice that the Cheshire eyepiece does not appear exactly centered inside the shadow of the secondary. Don't worry; this is in fact how things should look because the secondary mirror is slightly offset. (For more on the subject of secondary offsets, go to this sidebar. But bear in mind that you needn't master the somewhat elliptical reasoning behind the subject in order to collimate your telescope well!)

当完成第3步后，光轴就精确地位于调焦座中央了，大功告成。然而，如果你仔细一点的话，你会发现，Cheshire目镜在副镜中的反射像并不是完全居中的。不要担心，这是因为副镜实际上有偏差的。若想了解更多，可以看另一篇文章介绍Sidebar的。要记住你不必非得掌握椭圆的理论就能把光轴调好。

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A laser collimator is often used for Step 3, by centering the returning beam on the laser's faceplate. However, this method has problems that belie the laser's presumed accuracy. Why? Suppose that in Step 2 the laser beam has missed the true center of the primary mirror by a small distance, for example, 2 mm. Even if the primary mirror happens to be exactly collimated (its center precisely aligned with the center of the eyepiece), the returning laser beam will be parallel to the main mirror's axis but will miss the center of the laser faceplate by 2 mm. If you then tilt the main mirror to center the beam returning to the laser, the collimation will be 1 mm off! Unintentionally, you will have caused a miscollimation great enough to affect the performance of a short-focal-length telescope. This extreme sensitivity to a small and otherwise unimportant error in Step 2 is the Achilles' heel of the laser collimator. So even if you use one for rough alignment in Step 3, it is better to use a Cheshire eyepiece for the final adjustment.

激光器也常在第3步中使用，把激光的反射光调整到中央。但是，该方法与激光的精确性之间有差距。为什么？假定第2步中激光错过了主镜的中央点，误差只有一点点，例如2毫米。即使主镜完全调整好了，返回的激光束将平行于主镜的光轴，但将错过激光器的面板2毫米。如果你又调整了主镜，把光束居中的话，调整后的镜子将有1mm的偏差。无意之中，你已经把短焦比的镜子的性能大打折扣了。这是在第2步中使用激光器的局限性。所以即使你第3步调整的粗一些，我也推荐你使用Cheshire 目镜做最后的调节。

Star-Testing Your Collimation 星点实验

Once your telescope has cooled down and is well collimated, it should be ready to perform at its best. At high magnification (25× to 50× per inch of aperture, or 1× to 2× per mm of aperture) and in good seeing conditions, stars at focus should appear in the eyepiece as tight, symmetric diffraction disks. However, if stars at the center of the field show the telltale asymmetry of coma, double-check your collimation with the Cheshire eyepiece. If the center spot still looks centered, then it isn't located at the primary's true optical center.

一旦你的望远镜已经冷却，并调整好，就可以观测了。在高倍下(25× to 50× per inch of aperture, or 1× to 2× per mm of aperture)，大气宁静，星光汇聚应该呈现出致密的，对称的光衍射环。然而，如果星光呈现拖尾巴的慧差，一定要用Cheshire目镜检查。如果中央点还是居中的，说明它并不是真正的主镜的中央点。

If this is the case with your mirror's center spot, ignore it for now and try tweaking the primary's collimation, in small steps, until you have centered the best image in the field of view. (This method was described in detail in the June 2001 issue of Sky & Telescope, page 125, and is illustrated below.) The Cheshire will now indicate the location of the primary mirror's true optical center. If necessary, move the spot to the correct position or put another, larger piece of tape on top of it.

如果是镜子的中点出了问题，眼下不必管它，继续调整主镜，经过几个步骤，直到你看到最佳的图象。（该法在2001年的skyandtelescope中，125页有介绍。）使用Cheshire目镜将提示出此刻主镜的真正光学中央点。如果需要的话，把黑胶布的位置贴过去。

If you know that your primary mirror spot is okay (and in most cases it will be, if carefully centered), there is no need to routinely fine-tune your collimation with a star test — the Cheshire eyepiece is not only easier to use, but it is more accurate if the seeing is less than ideal, which it is most nights.

如果你知道你的主镜点是调好的，就不必经常做星点实验了——Cheshire目镜不仅容易使用，而且更精确。

Now your telescope is in perfect tune, and the improvement in performance should be obvious. If not, try to deliberately miscollimate the primary, and see what it does to a high-magnification view of a planet. After this demonstration, you'll never let your scope go out of collimation again.

现在你的望远镜就调好了，性能的改进应该是很明显的。如果没有达到的目的，仔细地调整主镜，看行星的表面在高倍下有什么变化。经过讲解，你已经掌握调整过程了吧。

天文一年级

Nils Olof Carlin is a telescope maker and self-taught collimation expert living in southern Sweden. A comprehensive collimating FAQ can be found at his Web site: http://w1.411.telia.com/~u41105032/.


尼尔斯.奥罗夫.卡林是瑞典南部一个望远镜制造者和自学成材的调校专家。很多有关问题可以在他的网站找到：http://w1.411.telia.com/~u41105032/.

伊柔星

我正好有个反镜，这下知道如何测试了

DLM

摘自哪的商业性质的文章。我不想知道文章的出处，不要告诉我。

美丽的星空

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1290982

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感谢分享

njit

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孤狼

帮顶，这帖子绝对值得保存200年， 还是双语的。谢谢版主

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帮顶

dust_38

好贴，翻译的辛苦