本帖最后由 弼马温1984 于 2018-4-24 19:40 编辑
译者：@DOB-YIN
说来惭愧，本节翻译在月初就完成了，事情有点多，耽误了很长时间，另外我觉得不翻几处毛病出来好像显得我太菜了，奈何翻译得实在太好了，鸡蛋里面挑不出骨头。
6.2 Constructing the Secondary Cage
构建副镜框
The secondary cage is the second major component you will build. The primary reason for building it so early is to get an accurate weight so that when you dimension the mirror box and truss tube, the whole thing will balance. It is not necessary that you complete every step in the construction, but you absolutely must finish everything that influences its weight.
副镜框是我们将要制作的第二个主要部件。 这么早就做副镜框主要是为了得到其准确的重量，这样，我们就可以确定主镜箱和桁架管的尺寸，让整个主镜达到平衡。你不必完成副镜框制作的所有步骤，但你必须完成所有影响其重量的事情。
In the foregoing sections. you have determined:
•The inside diameter of the secondary cage,
•The minor axis of the secondary mirror, and
• The (optional) secondary mirror offset.
在前面的部分，你已经确定了：
•副镜框的内径，
•副镜的短轴，以及
•（可选的）副镜的偏移量（offset）。
Before you can weigh the completed or semi-completed secondary cage. You need the following:
• the low-profile focuser,
• the spider assembly.
• the secondary mirror holder,
• the secondary cage finder (we recommend a Telrad). and
• one eyepiece of the type you plan to use most often.
Order these parts early so you won't have to stop working if delivery takes a while.
在称重已经完成或即将完成的副镜框之前，我们需要准备以下东西：
•短款调焦座，
•副镜支架组件，
•副镜座，
•副镜框寻星镜（推荐Telrad品牌），以及
•你计划最经常使用的一个目镜。
尽早订购这些部件，这样即使发货出现延迟，也不会对望远镜自作工期造成影响。
Before purchasing wood, reread Chapter 3 and at the very least, browse Appendix A on plywood. We trust that you are convinced of the value of solid hardwood multi-ply plywood for the rings in the secondary cage. Plywoods like ApplePly and Baltic Birch really are worth the extra money. They have twice as many layers and virtually no "holes" or voids. These plywoods provide more strength per unit volume than softwood plywood, so you can make narrower, and therefore lighter, rings. If you must use softwood plywood. make the rings wider and thicker to compensate for the weakness of the material.
在购买木材之前，建议把本书第3章再读一遍，或者至少浏览一下附录A关于胶合板的内容。我们坚信，你会认识到使用硬木多层胶合板制作副镜框的价值。使用苹果木和桦木制作的胶合板，他们的层数几乎是其他种类胶合板的两倍，并且几乎没有空洞。每单位体积的硬木胶合板比软木胶合板提供更大的强度，所以你可以制作更窄更轻的环。如果你只能使用软木胶合板，则需要把环做的更宽、更厚，以弥补材料的弱点。
For apertures from 15.5 to 20 inches, the rings should be fabricated from 5/8-inch hardwood veneer hardwood core (HVHC) plywood. For 22- to 40-inchers, use 3/4-inch HVHC plywood.
直径15.5至20英寸的环，应由5/8英寸厚的硬木板硬木芯（HVHC）胶合板制造。 直径22到40英寸的环，请使用3/4英寸厚的HVHC胶合板。
The rings should be 1.5 to 3 inches wide depending on the size of your scope and the type of plywood you use. For a 20-inch telescope, we recommend making the rings 1.75 inches wide. This leaves 1/4 inch of wood on either side of the 1.25-inch aluminum strut tubes that run between the rings. Earlier, we saw that the inside diameter of the secondary cage of a 20-inch f/5 telescope should he 21 inches. Using rings that are 1.75 inches wide means the outside diameter of the rings will be 24.5 inches. Since hardwood plywood is expensive, decide how you're going to place these big rings on the sheet. Make a drawing of the plywood sheet at 1:8 or 1:10 scale and move the circles around to use the sheet effectively. Sometimes it's heartbreaking to see how much wood you'll waste.
环的宽度通常应为1.5至3英寸，具体取决于望远镜的尺寸和所使用胶合板的类型。 对于20英寸的望远镜，我们建议环宽1.75英寸。 这样在1.25英寸铝质支撑管的两侧和环的边缘之间还有1/4英寸的木材。 上文我们知道20英寸f / 5望远镜的副镜框的内径应该是21英寸。 使用1.75英寸宽的环意味着环的外径将是24.5英寸。 由于硬木胶合板价格昂贵，因此要好好考虑如何将这些大环放在板材上。 按1：8或1:10比例绘制胶合板图纸，移动圆圈，看如何能更有效使用板材。 有时看到那么多板材被浪费真是让人痛心。
6.2.1 Order the Spider, Secondary Holder, and Focuser
订购副镜架、副镜座和调焦座
See Appendix E for suppliers of spiders and secondary holders. For a 20-inch telescope with rings that measure 21 inches across the inside diameter, you would order the 21-inch custom extra-heavy-duty spider. "Extra-heavy-duty" means the spider vanes are wider and have two set of mounting studs on each vane.
有关副镜架和副镜座的供应商，请参阅附录E. 对于主镜口径20英寸、环内径为21英寸的望远镜，可以订购21英寸的超重型副镜架。 “超重型”意味着叶片较宽，每个叶片上有两组安装螺栓。
If you plan to mount the secondary mirror centered in the tube, order a standard secondary holder sized to fit the secondary mirror you have ordered. If you plan to offset the secondary mirror, ask for a secondary holder with a built-in off-set. (You will need to specify the offset for your telescope.) Since an offset secondary holder is a custom order, expect to pay a premium price. Alternatively, you can order an undrilled secondary holder and then drill and tap an offset hole in the secondary holder yourself, or you can order a standard holder and make a small adapter that displaces the secondary minor holder by the correct offset distance.
如果你计划在镜筒中央安装副镜，请订购一个尺寸与你的副镜相匹配的标准副镜座。如果你要考虑副镜偏移，请选购有内置偏置的副镜座。（你需要确定针对你的望远镜的副镜偏移量。）由于带偏移的副镜座是客户定制的，价格会高一些。 或者，你可以订购一个未钻孔的副镜座，然后自行钻出副镜座上的一个偏移孔，或者你可以订购一个标准副镜座，并制作一个小型适配器，使副镜座移动正确的偏移距离。
As we discussed in Section 4.4, the height of the focuser influences the size of the secondary mirror and the need for baffling. "Ultra-low-profile" focusers (focusers less than 2 inches tall) may allow stray light to enter the eyepiece. so if you order one of these, be prepared to add some extra baffling. "Standard" focuser units that stand 4 or more inches tall can cause vignetting at the edge of the field of view， especially with fast mirrors, so we recommend that you avoid these. The best compromise is often a low-profile focuser that stands between 2 and 3 inches high when it is fully racked in.
正如我们在第4.4节中讨论的那样，调焦座的高度影响副镜的尺寸以及是否需要遮光板。 “超短”调焦座（调焦座高度小于2英寸）可能会让杂散光进入目镜，所以如果你订购了一个超短调焦座，就要准备好添加一些额外遮光板。 “标准”调焦座高度至少有4英寸，可能会在视场边缘造成渐晕，尤其是短焦比镜片，所以不推荐这种标准调焦座。最好的折衷方案通常是一个最小高度在2到3英寸之间的调焦座。
6.2.2 Cut the Rings
切割圆环
To mark circles on the plywood, make a "stick compass:' At one end of an approximately 1/2- by 1/2-inch stick of the proper length, drill a hole just big enough to hold a pencil snugly. Measure from the pencil point to the desired radius, that is, at half the diameter, and there drill a pilot hole for a small finishing nail. The nail should fit tightly.
为了在胶合板上画出圆圈，需要自制一个“棒状圆规”。找一根适当长度的大约1/2×1/2英寸的木棒，一端钻一个刚好插入铅笔的孔，从铅笔处测量所需的半径，即直径的一半，并且在那里钻一个小的导向孔，钉入小圆钉，钉子和木棒应紧密配合。
Locate the center of the hole where your scale drawing indicated you would use the sheet most efficiently. Tap the nail lightly into the plywood so it can't wander as you swing the compass. Draw circles for both the inside and outside diameters. Next—and this is important—use a straightedge and protractor to mark eight points. Four of these arc for the struts and four for the truss-pole attachments.
接下来确定圆心，就是用前面按缩小比例绘制的图，以便于我们最高效利用板材。然后将钉子轻轻敲入胶合板，确保圆规转动时不会晃动。把需要的内、外圆都画出来。 接下来，很重要的一点是，使用直尺和量角器来标记八个点。 其中四个用于安装支柱，四个用于安装桁架杆附件。
Check to be sure these eight points are equidistant, that is, 45° apart. If they are not, the spider vanes will be slightly out of line and you'll have stars with eight-spike diffraction patterns instead of four spikes. Mark these points before the rings are cut because it's difficult to mark them later, when the center of the circle is gone. Overlooking a detail like this can force you to waste an afternoon salvaging what might otherwise have been an easy task.
检查一下，这八个点应该是等距的，即相隔45°。如果它们不是，那么副镜架叶片的位置就会偏，将来我们观测时看到的衍射星芒会是8根，而不是我们希望的4根。 在环被切割之前标记这些点，因为当圆的中心消失后就很难标记它们了。忽视这样的细节，可能会迫使你浪费一个下午来挽回原本是一件很容易的事情。
If you have a saber saw, cut along the outside diameter and remove the disk of wood. Although it isn't strictly necessary, removing the excess makes cutting precise circles easier work for the router. As you cut, stay close to the outside of the line without touching it.
如果你有一把马刀锯，可以先沿着外径把需要的材料从整张木板上切割下来。虽然这不是必须的，但后面用电木铣精确切圆时，可以更容易一些。在切割时，请保持靠近线的外侧而不要触及它。
To rout a ring from plywood, attach the plywood disk to the bench top with eight small wood screws. Insert four of the screws where the four struts will later attach so that you do not have to snake extra holes in the rings. Countersink the screw heads so they do not interfere with the motion of the router. Screw the inner disk to the bench top with the other four screws-hut you need not worry about the screw locations because the inner disc is scrap. Screwing the disc to the bench top is better than clamping it because the clamps get in the way of the router and you can't clamp the inner disc anyway. With both the ring and the inner scrap disc firmly screwed down to the bench top you can confidently cut out the ring.
要把圆环从胶合板切下来，首先要把胶合板固定在工作台上。推荐的方法是用八个小木螺钉，其中四个可以钉在环上将来放支柱的位置，这样我们就不必在环中打多余的孔了，另外四个钉在内部圆盘上， - 因为内部圆盘是废料，所以螺丝位置可以任意选。一定要用沉头螺丝，这样就不会干扰电木铣的运动了。有人可能想也可以用夹子把胶合板固定在工作台上，但这样会妨碍电木铣的工作，而且内部圆盘是无法夹住的。现在，我们将环和内部圆盘牢固地拧到工作台上，就可以放心地开始切割了。
If you have a circle-cutting attachment for your router. attach the pivot point to a bolt through the center of the disc. Most routers have some fairly convenient places to attach such accessories. If you don't have one of these attachments，mount the router on one end of a piece of 1/4-inch scrap plywood. At the other end of the plywood, drill a hole at the desired radius for the bolt. Remember that for the inside cut, you must measure from the outside of the router bit. and for the outside cut，you must measure from the inside of the router bit. Secure this radius-cutting jig with a 1/4-20x2-inch carriage bolt through the Center of the disc. The idea is that the router should not be able to wander, so drill a hole slightly undersize and press the bolt through from the underside. Drill a matching 1/4-inch hole in the router attachment—be sure you have a snug fit on the bolt so there won't be any wobble.
如果你的电木铣有切圆的附件，则通过其中心定位孔，用螺栓与木圆盘的中心孔连接。大多数电木铣都有方便连接这些附件的位置。如果你没有切圆附件，可以将电木铣安装在一块1/4英寸（厚？）废胶合板的一端，并在胶合板的另一端，在所需的半径位置钻一个孔，然后用螺栓和木圆盘中心孔连接。测量时请记住，对于内部切割，必须从铣刀的外部进行测量，而对于外部切割，必须从铣刀的内部进行测量。螺栓可以选用1/4-20x2英寸（接近M6*50）的方颈螺栓（译者：方颈螺栓紧固木材有自锁功能，淘宝搜 方颈螺栓）。关键是要保证电木铣不能有晃动，所以钻的孔最好小一点，并从底部压入，螺栓和孔是紧密配合的，这样才可以防止电木铣晃动。
（译者备注：英制螺栓规格1/4-20x2的含义：螺纹直径1/4英寸，牙距20（一英寸内有20个牙），螺纹长度2英寸）
The distance between the bolt hole in the plywood router attachment and the router bit should be the radius you desire for the cut. Check the radius on a scrap piece of plywood. If the radius it too large or too small, drill another 1/4-inch hole in the plywood attachment at the correct radius. It may take several tries before you get it right. Using this method, the upper and lower secondary cage rings are guaranteed to be exactly the same dimensions.
铣刀和胶合板切圆附件定位孔之间的距离应该是我们需要切割的半径。可以先找一块胶合板废料确认一下切割的半径。 如果半径太大或太小，请在胶合板附件上以正确的半径再钻一个1/4英寸的孔。经过几次尝试后，可以准确得到所需要的半径。使用这种方法，保证副镜框的上环和下环的尺寸完全符合预期。
Use a good quality carbide router bit to make the cuts. Ordinary high-speed-steel bits may be cooked black after the first ring is cut, so don't cut corners when it comes to buying a bit. The glue layers in hardwood ply are very hard, and they will dull the tool quickly. Sharp tools are safer than dull tools, and cheap tools usually get dull quickly. You may as well spend the money-you'll need this router bit again and again, when it comes time to cut the ground board, the side bearings, and the rocker side arcs.
使用高质量的硬质合金铣刀来进行切割。 普通的高速钢铣刀通常在切割完第一个环后可能会发热变黑，所以在购买工具时不要偷工减料。 硬木多层板中的胶层非常坚硬，它们会使工具迅速钝化。锋利的工具比钝化的工具更安全，便宜的工具通常很快变钝。除了切割副镜框的环，铣刀还会用在切割望远镜的底板、侧转轴弧面和底座的侧转轴支撑弧面，因此多花点钱买好一些的铣刀是值得的。
If you have never used a router before, get someone who knows how to show you the ropes. Go slow and be careful. Wear eye protection and keep your fingers away from the bit. You will be delighted at what a fine job the router does, but when the router bit is cutting, chips fly in all directions and the cutter is, well, a cutter, and fingers are softer than plywood. If you have a phobia about using high-powered tools, get someone who is comfortable with them to do the job for you. Promise the moon and stars—after all, you can deliver!
如果你之前从未用过电木铣，最好找一个高手向你展示一下使用技巧。刚开始要慢一点，小心点。 护目镜是必需的，手指头要离刀头远一点。电木铣的切割效果是令人满意的，但电木铣切割时，会有碎片飞溅，手指头比胶合板软，碰到刀头就会受伤。如果你对这种大功率电动工具有恐惧感，还是请别人帮你完成这个工作吧。能顺利完工是最重要的。
Cut the outer diameter in several passes. Make the first pass a very shallow cut through the top veneer or two. This severs the wood fibers and prevents the face veneer from lifting during subsequent passes. If you are cutting high-quality hardwood plywood，take three or four trips around the circle, each time lowering the cutter a little bit，to cut all the way through.
用电木铣切圆，不要想着一刀就切完，而要多走几刀。第一刀通常切的很浅，切开顶部的一两层，这样切断了木纤维，防止在随后的切割过程中表层饰面被抬起。切割高质量的硬木胶合板，通常需要走三或四刀，每次将切刀逐渐降低，直至完成整个圆环切割。
After the outside cut is made. move the router in and rout the inside diameter. As before. cut the ring in several passes. After you've made the cuts, unscrew the ring and check your work. The cuts should be clean, sharp-edged, and smooth. It is very satisfying to produce a couple of nearly perfect rings in a fine plywood.
切割外圆完成后，移动电木铣，开始切割内圆。和前面一样，要多次进刀。切割完成后，拧下固定螺丝取下圆环并检查。切口应该干净，锋利，光滑。 在优质的胶合板中切割出几乎完美的环，是非常惬意的。
Gently round the inside edges with sandpaper to prevent the grain from catching your knife blade when you trim the Kydex light baffle later on. Radius all the outer diameter edges of the rings with a 1/8 inch radius router bit. This will leave them rounded and smooth to the touch. The outside edges are visible, and during setup and observing they are handled extensively. Spend some extra time to finish the outer end grain edges so they look smooth and attractive. Fill and sand any end-grain voids.
对环的内边缘，可以用砂纸轻轻地将打磨，这样在稍后修剪Kydex遮光板时就不会被板子上的毛刺影响。对环的外边缘，可以用半径为1/8英寸的铣刀处理一下，这将使他们圆润，触感柔滑。环的外部边缘是可见的，并且在安装和观测期间手会经常触摸。多花点时间处理外边缘是值得的，让它们看起来光滑、漂亮。如果发现外边缘有空隙，需要（用腻子）填充并打磨平整。
The plywood ring cut-outs are scrap. They are too small for a ground board, so forget about that right now. Maybe you can give them to someone for making a smaller Dobsonian. Or make a Lazy Susan for the dinner table, and have rotating mashed potatoes.
切下来的胶合板圆片在接下来的做望远镜的步骤中是用不到了。用它们来做底板太小了，所以现在就忘记它们吧。 也许你可以把它们送给其他想做小一些的道布森望远镜的人，或者做一个餐桌转盘，享用旋转土豆泥。
6.2.3 Make Three Rings for "The Big Ones"
给“大块头”做三个环
Secondary cage rings for telescopes in the larger-than-25-inch class are just the same as those for smaller telescopes, except that you should use seven struts. Four of these struts support the spider and the other three provide extra support for the cage rings. The secret behind the construction of secondary cages is that the thin plastic light baffle, wood rings, and struts all weigh very little. However, even the lightest cage can become unwieldy to carry up a ladder and attach to a set of truss poles on apertures larger than 25 inches. "The Big Ones" require an auxiliary connecting ring to hold the eight truss poles in alignment. Why is this? In smaller telescopes, the observer scampers up the ladder with the secondary cage and leans away from the ladder, and deposits the secondary cage atop the truss poles. It works, and it's quick and easy.
大于25英寸等级的望远镜的副镜框与小型望远镜的副镜框基本是一样的，但应使用七个支柱。其中四个支柱支撑副镜支架，另外三个为副镜框环提供额外的支撑。制作副镜框的秘诀在于：遮光板、木环和支柱的重量都很小。然而，当我们拿着副镜框爬上梯子，并将其连接到25英寸孔径范围的一组桁架杆上时，再轻的副镜框也会显得很笨重。 “大块头”望远镜需要一个辅助连接环来保持八个桁架杆对齐。 为什么要这样？ 在较小的望远镜中，观察者带着副镜框爬上梯子，并从梯子上侧身将副镜框放置在桁架杆顶上，这是可行的，而且快速、简单。
"The Big Ones" call for a different approach. Reaching out with a secondary cage the size of a bass drum and setting it atop the truss poles is a tall order. For example the secondary cage for a 30-inch telescope weighs around 25 pounds and is an ungainly 3 feet across. There is considerable danger that the observer and the secondary cage could plummet into the mirror box.
但对“大块头”望远镜，应采取不同的方法。 举起一个像低音鼓大小的副镜框，并将其放置在桁架杆顶上，是一项艰巨的任务。 例如，30英寸望远镜的副镜框重约25磅，跨度约3英尺。观测者和副镜框可能掉下来坠入主镜箱，这样存在相当大的危险。
The safe solution is to assemble the telescope horizontally. With both feet securely on the ground, you simply walk over with the secondary cage and connect it to the connecting ring. Figures 11.17 through 11.20 show how this works. The connecting rings hold the tips of the poles together and also supports the secondary cage.
安全的解决方案是：在水平状态下组装望远镜。 这样我们就可以在地面上平稳地走动，拿着副镜框，并将其连接到连接环即可。 图11.17至11.20显示了这是如何工作的。 连接环将桁架杆的顶端固定在一起，并支撑副镜框。
6.2.4 Drill the Strut Seats
钻出支柱座
Four struts join the two plywood rings. The struts themselves are aluminum tubing, the same stuff you will later use for the truss tube poles. Recessed holes cut to the diameter of the struts locate and help the struts to seat properly, and they also prevent the struts from pulling inward under tension of the spider vanes. (More about struts below.)
四个支柱连接着两个胶合板环。支柱本身是铝管，和桁架管是同样的材料。按支柱的直径钻出定位孔，可以帮助支柱安装到正确的位置，并且可以防止支柱在副镜支架叶片的张力下向内拉动。（下面有更多关于支柱的介绍。）
Align the two plywood rings and clamp them together. Because the outer edges of the rings are rounded slightly, it looks better if you place the strut mounting holes about 1/8 inch inward from the center of the ring. Drill 1/8-inch locating holes through both rings at the four strut locations. Before you unclamp the rings. mark their orientation so you know which pairs of holes match up perfectly. Then, using a spade bit or Forstner bit, countersink the four 1.25-inch strut-mounting holes to a depth of 1/16 inch into one side of each ring at the four points you marked with location holes.
对齐两个胶合板环并将它们夹在一起。由于环的外边缘稍微变圆，在确定支柱安装孔位置时，可以从环的中心向内移约1/8英寸，这样看起来更好一些。在四个支柱安装位置，用1/8英寸钻头，穿透两层环钻出定位孔。 松开夹子之前，做个定位标记，以便知道哪些孔是正对的。 然后，使用铲形钻头（木工扁钻）或Forstner钻头（木工开孔器），在标有定位孔的四个点上，在每个环的一侧，钻出1.25英寸的支柱安装孔，深度1/16英寸。
On the lower ring. the remaining four marks between the strut to locations show where to place the truss pole attachments. If you already have the truss pole attachments, drill pilot holes for the screws that will later hold them in place. Stain, seal and varnish both rings. Congratulations! The rings are finished.
在下环的支柱之间，还有四个标记，那是桁架杆附件的放置位置。 如果你已经有桁架杆附件，就钻出用于其固定的螺钉导向孔。 然后给两个环染色、密封和刷清漆。恭喜你！环已经完成了。
6.2.5 Make the Struts
制作支柱
The length you choose for the struts determines the length of the secondary cage. To prevent stray light from reaching the secondary or entering the eyepiece on a 20-inch telescope, the secondary cage should be a minimum of 12 inches long, and proportionately longer on bigger scopes. Here is another rule of thumb:
Cut the struts to 60% of the primary mirror diameter.
支柱的长度决定了副镜框的长度。为防止杂散光进入副镜或目镜，20英寸望远镜的副镜框至少应该有12英寸长，对更大的望远镜，副镜框也要等比例加大。这是另外一个经验法则：
支柱长度应为主镜直径的60%
A 25-inch Dobsonian would, for example, need struts 0.60 times 25, or 15 inches long. This rule of thumb does not provide complete baffling. Purists recommend that baffling extend above and below the secondary mirror at least one full diameter of the primary, which on a 20-inch scope results in a secondary cage 40 inches long. Think about it: To assemble the telescope, you will have to carry the secondary cage up a ladder at night by yourself. The length we recommend is easy to handle and provides baffling that is entirely adequate for reasonably dark sites.
例如，25英寸的道布森望远镜的副镜框支柱长度是25*0.6，即15英寸。这个经验法则并不提供完整的遮光能力。单纯从理论上讲，应该在副镜的上方和下方延伸至少一个主镜直径的遮光物，但这样就得为20英寸望远镜配备40英寸长的副镜框。想一想组装望远镜时，需要在晚上自己带着这么大的副镜框爬梯子，还是算了。因此我们推荐更易于使用的副镜框长度，对一般的黑暗场所这个遮光能力是完全可以接受的。
The main cause of image fogging is stray light entering through the top of the telescope opposite the focuser. Light sneaking in below the Kydex baffle will usually be blocked by the full-length cloth shield over the truss tube. If the Kydex above the focuser extends 1/3 the primary's diameter above die center of the focuser, sky light cannot reach the eyepiece. On a 20-inch telescope, position the spider and secondary so that the focuser is at least seven inches from the upper end of the secondary cage. On very large telescopes, you can place an auxiliary light baffle made from a short length of Kydex opposite the focuser at the top of the tube. Attach this extra baffle with Velcro so it can be placed and removed easily. See Figure 12.11.
让图像起雾的主要原因是在调焦座对面通过望远镜顶部来的杂光。在Kydex遮光板下方过来的光线通常会被桁架管上的遮光布挡住。如果Kydex遮光板能从调焦座中心往上延伸1/3主镜直径，则天空中的杂散光就不能到达目镜。在一个20英寸的望远镜上，副镜支架和副镜的位置，决定了调焦座距离副镜框顶端至少七英寸。在非常大的望远镜上，你可以将一段用Kydex制成的辅助遮光板安放在调焦座对面的副镜框顶部。用魔术贴固定它，以便轻松地安装和移除。 见图12.11。
The struts separating the two plywood rings are made from the same tubing used for the truss. We recommend aluminum tube 1.25-inch O.D. for telescopes 22-inches and under, 1.5-inch O.D. for 24- through 30-inchers, and 2-inch 0.D. for32-, 36-. and 40-inchers. The 1.25 -inch tubing is available at most hardware stores or lumberyards, and is sold in six-foot lengths. The wall thickness should he about 0.055 inch.
支柱用来分离两个胶合板环，其制作材料是与桁架杆相同的管子。对于22英寸及以下的望远镜，我们推荐外径1.25英寸的铝管，24英寸到30英寸的望远镜，推荐用外径1.5英寸的铝管，32英寸、36英寸和40英寸的望远镜，推荐用外径2英寸的铝管。大多数五金商店或伐木场都有1.25英寸的铝管，并且以六英尺的长度出售。 壁厚应该约为0.055英寸。
Cutting thin-wall aluminum tube is a snap with a tool called a tube cutter. You can get one at the hardware stone fur around $20. It will cut tubing to length more precisely than you can with a hacksaw. You might as well buy one now because you'll need it later for cutting the truss poles to length.
采用管子割刀切割薄壁铝管非常容易。这种工具在五金店有售，大约20美元。其切割精度比钢锯好的多。你现在可以买一个，因为稍后你还会需要它来切割桁架杆。
The location of the holes for the spider will depend on the dimensions of the spider you order. Normally, the holes turn out to be 1 to 2 inches from the upper ends of the struts. This means the upper end of the spider and secondary holder lie about 11/2 inches inside the secondary cage. After you have cut the four struts to length, drill the mounting holes for the spider.
（副镜支架通过支柱固定）。安装副镜支架的孔的位置取决于你所订购的副镜支架的尺寸。 通常，孔距支柱的上端1至2英寸。 这意味着副镜支架和副镜座的上端在副镜框内约1 1/2英寸。 在将四个支柱切成需要的长度后，钻出副镜支架的安装孔。
Fig. 6.11 A great way to insure that your struts have their holes in the same location is to construct a strut jig-a block of hardwood with holes drilled in the correct positions. On a drill press table，insert each strut and run a drill through the holes in the jig.
Fig. 6.11确保四个支柱在相同位置上钻孔的好方法：用硬木做一个支柱夹具，并在夹具的正确位置上开孔。把每个需要加工的支柱通过夹具固定在钻床上，通过夹具上的孔给支柱钻孔。
Fig. 6.12 Threaded inserts look like stiff metal flowers-and they work like the proverbial umbrella in a chimney. Attach a threaded insert to a bolt run through a small block of wood then press it into the tube. Once in place, the insert can not be pulled out. Also see Figure 8.20
Fig. 6.12 螺纹插件（译者：淘宝搜 太阳花弹片）看起来像僵硬的金属花 --其工作原理就像俗话说的烟囱里的雨伞（拔不出来）。将螺纹插件连接到穿过一小块木头的螺栓，然后将其按入管中。一旦到位，插件就拔不出来了。 另见图8.20
Fig. 6.13 Construction of the upper end of the secondary cage is shown in this cross-sectional view. The secondary cage rings support four struts, and the struts support the vanes of the spider which carry the secondary mirror. Double-sided foam tape secures the Kydex light baffle to the rings.
Fig. 6.13从这个剖面图中可以看出副镜框上端的构造。副镜框的环支撑四个支柱，支柱支撑副镜支架的叶片。双面泡沫胶带将Kydex遮光板固定到环上。
6.2.6 Attach the Struts to the Rings
将支柱固定在环上
Threaded inserts are used to attach the aluminum struts to the plywood rings on the secondary cage. There is no need to epoxy the tubing to the wood, and no need to use machine threaded plugs and press-fit them into the tubes. Threaded inserts are off-the-shelf metal "flowers" that you force into the tube and-presto-eliminate the hassles.
通常用螺纹插件（译者：淘宝搜 太阳花弹片）来连接副镜框的铝管支架和胶合板环。不需要用环氧树脂把铝管粘在木头上，也不需要使用机器螺纹塞并将其压入管中（？）。 螺纹插件是现成的金属“花朵”，您可以将其强制插入管中并预先消除麻烦（？）。
Simply press a threaded insert into each end of each strut. Run a short bolt through a hole drilled into a scrap of wood, screw an insert on that bolt and with a hammer tap the inserts into place-once inserted they never come out. An even niftier way is to put a machine screw into a drill press (obviously the drill press should not be running) and spin the insert on tip to the chuck. Stand the tube on the drill press table and press the insert into the tube by lowering the chuck with the handle of the drill press.
只需将螺纹插件按入每个支柱的每一端。一种方法是找一块木头，孔钻并固定一个短螺栓，在该螺栓上拧上一个螺纹插件，然后借助锤子，把螺纹插件插入铝管。一旦插入，螺纹插件就无法被拔出。另一种更加直接的方法是：借助钻床的卡盘固定螺栓和螺纹插件，将管子放在钻床台上，用钻床手柄降低夹头将螺纹插件插入管子（显然，钻床不应该运行）
You can now attach the rings to the end of the cage struts using ordinary 1/4-20 by1 1/4-inch machine screws. Best of all, threaded inserts allow for future disassembly if you need to rebuild that part of your scope. Threaded inserts are cheap, only about 55￠ apiece. They weigh next to nothing and come in assorted sizes and threads.
现在，你可以使用普通的1 / 4-20×1 1/4英寸机器螺钉将环安装到副镜框支柱的末端。这样的一个好处是，如果您需要重新构建望远镜的那部分，螺纹插件允许将来进行拆卸。螺纹插件价格便宜，仅售55美分（译者：淘宝 太阳花弹片标价每个不到一元）。它们几乎没有任何重量，并且有多种规格可以选择。
After you've inserted one into each end of the struts, assemble the secondary cage by passing the proper size machine screw through the ring and into the threaded insert of the strut. Congratulations! You have just created a strong, lightweight "cage" for the secondary mirror and focuser.
将螺纹插件分别插入支柱的两端后，通过将合适尺寸的机器螺钉穿过环并旋入支柱内螺纹插件中来组装副镜框。恭喜你！你刚刚完成了一个坚固而轻便的副镜框可以固定调焦座和副镜。
6.2.7 The Focuser Board
调焦座支撑板
The focuser board is a 1/4-inch thick piece of Baltic Birch or similar high-performance plywood with a reinforcing strip of wood on each side of the board. Don't get lazy and use a thick piece of plywood: we're trying to make the secondary cage as light as possible.
调焦座支撑板是一块1/4英寸厚的波罗的海桦木或类似的高性能胶合板，在板的每一侧都有一块加固带。不要偷懒使用太厚的胶合板，因为我们的一个目标是让副镜框尽可能轻。
Trim the focuser board to fit between the two rings of the secondary cage. Drill the hole for your focuser with a hole cutter. Be sure that the focuser hole will end up directly opposite the secondary holder. To be sure the alignment is accurate，mount the secondary holder so that there is an extra 1/4 inch between it and the spider hub. That way, if you miss slightly with the hole in the focuser board, you can reposition the secondary holder to compensate.
修整调焦座支撑板长度，使其正好可以放入副镜框的两个环之间。然后（根据调焦座底座大小选择合适的）木工开孔器在调焦座支撑板上钻孔。确保调焦孔正对着副镜座。确保校准准确无误，安装副镜座，使它与副镜支架之间有1/4英寸的距离。 这样，即使调焦座支撑板上的孔有少量偏差，也可以通过重新调整副镜座的位置来进行补偿。
Position the focuser hoard exactly between two of the struts. Secure it with some wood glue and a couple of drywall screws on each end.
将调焦座支撑板定位在两个支柱之间。然后用木工胶和自攻螺丝在两端固定。
6.2.8 Install the Kydex Light Baffle
安装Kydex遮光板
You can use any type of plastic or metal inside the secondary cage， but we strongly recommend Kydex. Kydex is inexpensive. It is waterproof. It is easy to cut and drill. It is dull on the inside (to absorb light) and shiny on the outside (so it looks good). It is black through and through, so if it gets scratched, it stays black. It accepts double-sided tape. It maintains its shape. It comes in long sheets so you can wrap a single piece around the whole secondary cage and hide the seam under the focuser board.
你可以在副镜框内使用任何类型的塑料或金属做遮光板，但我们强烈建议你使用Kydex板（淘宝：Kydex，热塑板，K板）。Kydex板价格不高，防水，易切割和钻孔。其内侧无光泽（吸收光线），而外侧光亮（看起来漂亮）。其内部材料也是黑色的，所以即使被刮伤，也会保持黑色。它易用双面胶带固定，不变形。可以买到长片材料，因此整个副镜框只用单张Kydex板就可以了，可以把接缝隐藏在调焦座支撑板下面。
Kydex is sold in 4- by 8-fool sheets in nine thicknesses from 0.028 inches on up. You want the 0.028 in black for the secondary cage light baffle; this stuff retails for $38 per sheet. It is primarily sold as a commercial wall covering. It won't dent like aluminum, yet it's nearly as light. If you feel creative, Kydex is available in a rainbow of colors and five surface patterns. And, as you will soon appreciate, it can he trimmed with a sharp knife and drilled for the spider screws.
市面上能买到的Kydex板通常是8英尺长4英尺宽，厚度从0.028英寸（约0.7毫米）往上共有9种规格。 如果采用0.028英寸厚的黑色用于副镜框遮光板，其零售价为每张38美元。Kydex板主要作为商业墙布出售。 它不会像铝一样凹陷，但几乎一样轻。如果你希望富有创意，Kydex有多种颜色和五种表面图案可以选择。而且，正如你很快就会意识到的那样，它可以用锋利的刀子修剪并为副镜支架螺丝钻孔。
But beware, Kydex deforms at 180 Fahrenheit. If you wrap your scope in clear plastic under the hot, daytime sun at a star party, the greenhouse effect will warp your Kydex. Always cover your scope loosely with one of those ubiquitous blue plastic tarps.
但要小心，Kydex板在180华氏度（约82摄氏度）下会变形。 参加星空派对时，如果白天你用透明塑料袋包裹望远镜，阳光照射下的温室效应会让Kydex变形。因此，最好用那种常见的蓝色塑料防水布覆盖你的望远镜。
Elsewhere in your telescope, you may have already used Kydex to retain the flotation cell triangles. Cut into a 2-inch-wide ring and attached with double-sided tape to tile apices of the triangles, the Kydex prevents the triangles from rotating, yet still allows them to pivot.
在望远镜的其他地方，你可能已经使用Kydex来让浮动支撑三角形定位。 切成2英寸宽的圆环，并用双面胶带贴在三角形的顶点上，Kydex可以防止浮动支持三角形（水平）旋转，但仍然允许它们（竖直方向）移动。
Double-sided tape is used to attach the Kydex to the secondary cage. Double-sided tapes are versatile. Cloth carpet tape，3M weather stripping tape，and automotive trim mounting tape are a few that work well in this application. Buy it in 1/2 -inch width, which is just right for holding Kydex inside the secondary cage.
用双面胶将Kydex固定在副镜框上。双面胶是多功能的。布基胶带、3M全天候胶带和汽车饰件安装胶带都可以用。购买1/2英寸宽度规格的，这恰好适合将Kydex粘在副镜框里。
Cut a piece to length using the formula for the circumference of a circle: C =π* IDsc. For a 20-inch telescope with the 21-inch rings, 21π equals 66 inches. Cut a piece this length and a couple of inches wider than the length of the secondary cage.
使用下面公式计算圆的周长：C =π* IDsc（副镜框内径）。 对于20英寸望远镜，副镜框的环的内径是21英寸，21*π等于66英寸。以此数据为长度，以比副镜框的高度多几英寸为宽度，准备好Kydex板备用。
Kydex has a mind of its own-it expands and contracts with temperature. Wrapping it into the secondary cage on a hot day or in a hot room is asking for trouble. It will contract enough on cold nights to separate itself from the inner surface of the rings. When you press it down in one place, it pops up somewhere else. It's maddening. Be clever. Roll up the Kydex and put it into your freezer. Or wait until night or for a cold day to wrap the Kydex. When it warms, you'll have a nice tight fit.
Kydex有明显的热胀冷缩特性。所以，如果在炎热的天气或高温的室内将其安装在副镜框，那是自找麻烦。它会在寒冷的夜晚收缩后导致从副镜框环的内表面分离。 当你在一个地方按下它时，它会在另一个地方弹出，这会让人很恼火。 聪明的方法是，先把Kydex卷起了并将其放入冷藏室使其降温，或者等到夜晚或冷天了，再来安装Kydex。当它变暖时，它会膨胀，可以和副镜框环贴合的更紧密。
Wrapping the Kydex inside the secondary cage is very tricky. If you want to reinvent the wheel, feel free to do so. but if you want to save time and materials, pay close attention to the following.
将Kydex安装在副镜框里是非常棘手的一件事。如果你想重新发明轮子，请随意。但如果你想节省时间和材料，请密切关注以下内容。
Apply a thin coat of contact cement to the inside edges of the plywood rings and let it dry. Contact cement yields a better bond with adhesive tapes than uncoated wood. Apply a layer of double-sided tape to the inside of both rings and remove the protective backing. On the inside of the focuser board, mark in pencil a starting line that is perpendicular to the plywood rings. Apply a length of double-sided tape adjacent to the line.
在胶合板环的内边缘涂一层薄薄的接触水泥(译者：contact cement,一类粘合剂，快干、防水、坚固，淘宝上海外有售，但国内暂未找到对应产品）并让它干燥。 与未涂的木材相比，接触水泥与胶带产生更好的结合。在两个环的内侧贴上一层双面胶带，然后取下保护层。 在调焦座支撑板的内侧，用铅笔标出与胶合板环垂直的起始线。在线附近贴上一段双面胶带。
Lay the secondary cage on its side on the work bench with the focuser board down. Roll the length of Kydex tightly into a roll a few inches across. Remember, dull side in. shiny side out. Starting behind the focuser board, align the edge of the Kydex with the pencil line on the focuser board. Press the end of the roll down onto the plywood rings evenly.
将副镜框放置在工作台上，调焦座支撑板朝下。将Kydex板按长度方向紧紧卷成几英寸宽的卷。记住，Kydex板的亚光面朝内，闪亮面朝外。从调焦座支撑板后面开始粘贴，将Kydex板的边缘与调焦座支持板上的铅笔线对齐，将卷筒的末端均匀地压在胶合板环（的双面胶）上。
Unroll the Kydex gradually, proceeding around the secondary cage by rolling it on the bench as you go. After you're all the way around, trim away the excess along the top and bottom of the secondary cage with a very sharp utility knife. Try not to mar the wooden rings with the blade. If you beveled the inside edges a bit, the blade won't catch as easily.
逐渐展开Kydex板，副镜框同时在工作台上滚动。 在完成之后，用一把非常锋利的美工刀沿着副镜框的顶部和底部修剪掉多余的Kydex板。尽量不要让刀片损坏木环。如果你把刀片稍微向内部边缘倾斜，则刀片不会轻易割到木环。
Here is another trick. Although Kydex is quite resilient, when it is creased or hit hard，it shows a dull, whitish mark. Warm the area-gently, gently, gently-with a heat gun or blow torch and the mark magically goes away. It' you heat the Kydex too strongly, you'll melt a hole in it. Go easy when you apply the heat.
这里还有另外一个窍门。虽然Kydex具有相当的韧性，但当它出现折痕或受到重创时，会出现无光泽的白色痕迹。 用热风枪或喷枪非常轻柔地加热这个区域，白色痕迹就会魔术般地消失。但如果加热的太猛，Kydex会融化出一个洞。所以加热时要小心一点。
6.3 Connecting Ring for "The Big Ones"
为“大块头”做的连接环
The connecting ring is a single plywood ring exactly the same dimensions as the two rings of the secondary cage. The connecting ring has the eight truss pole fasteners permanently mounted to it on one side and on the other side， simple snap latches that mate with catches on the secondary cage. (Snap latches can be found at most hardware stores, marine supply outfits, and Reid Tool Supply. They arc commonly used on tool boxes to keep the lid closed tight.)
连接环是与副镜框的两个环同直径的单层胶合板环。连接环的一侧固定安装有8个桁架杆紧固件，另一侧装有扣锁，用于连接副镜框。（扣锁在大多数五金店、海运设备供应店或Reid工具供应店可以买到。它们通常用在工具箱上以保持盖子紧闭。）
The connecting ring is light just five pounds for a 36-incher--so you can carry it up a tall ladder with one hand, set it on top of pole tips. and clamp the poles in place. See Figures 11.17 and 11.18. Once the truss is locked together with the connecting ring, you can safely lower the tube to a horizontal position. There is no need to worry about pole failure or splitting a pole block, because the eight poles share the load.
适合36英寸望远镜的连接环仅重5磅 - 因此你可以用一只手拿着它并爬上一架高的梯子，将其安装在桁架杆的顶端，并将桁架杆夹紧到位。见图11.17和11.18。一旦桁架与连接环锁定在一起，就可以安全地将镜筒放到水平位置。因为有八根杆子来分担负载，所以不必担杆子或接头破裂。
Attached to the connecting ring is a short length of rope with a safety hook on the end, the same kind used on dog leashes. After pulling the telescope horizontal, you secure the connecting ring to a heavy object on the ground. A cement block, the bottom of your ladder, a car bumper, or anything else substantial can hold the telescope.
在连接环上系一段短的绳索，尾部有一个安全钩，与狗皮带上使用的绳索类型相同。将望远镜拉至水平位置后，将连接环固定在地面上的重物上。 水泥块、梯子的底部、汽车保险杠或其他任何实体都可以固定望远镜。
The secondary cage has a pair of hooks on the bottom ring. so you carry the secondary cage over and hang it on the connecting ring by the hooks. With your hands free, you engage the latches. After the secondary cage is latched onto the connecting ring, the telescope is balanced. You can undo the rope hook and tilt the telescope upwards to observe.
副镜框的底环有一对钩子，可以通过钩子把副镜框挂在连接环上。腾出手后，你可以用扣锁把副镜框锁定在连接环上。此时望远镜是平衡的。你可以拆掉绳子和安全钩，向上倾斜望远镜以便观测。
Take down is the reverse. The most important thing to remember is this: Secure the rope to the connecting ring to a weight on the ground before you remove the secondary cage. As soon as you detach the secondary cage, the telescope becomes quite unbalanced. You could get hurt and the telescope could be damaged as the poles swing to the upright position.
拆卸是相反的过程。千万要记住的是：在拆下副镜框之前，一定要将连接有安全钩和地面重物的安全绳系在连接环上。 否则一旦拆下副镜框，望远镜就会变得非常不平衡，桁架杆会摆动到直立位置，这个过程可能让你或望远镜受伤。
As a safeguard, we strongly recommend that you attach a second rope from the connecting ring to the secondary cage. If you forget to secure the telescope to the ground, the unbalanced truss assembly will rise as you try to lift the secondary cage. and the rope will prevent you from removing it completely.
为安全起见，我们强烈建议你用第二根绳子将连接环和副镜框连在一起。 如果忘记将望远镜固定在地面上，则在你尝试拆掉副镜框时，不平衡的桁架管会上升，这根绳子会帮助你防止副镜框被完全移走。
You need to attach the secondary cage on the connecting ring precisely the same way each time you set up the telescope. The simplest way to do this is with a couple of locating pins. The pins are nothing more than a pair of 1/4-20 carriage bolts located on the bottom ring of the secondary cage, spaced 180°apart and protruding far enough to pass through matching holes in the connecting ring. Glue them permanently in place. When you set up the scope, align the two bolts to the holes in the connecting ring and perfect collimation is assured.
每次安装望远镜时，都需要以相同的方式将副镜框与连接环固定（译者：否则光轴可能需要重调）。 最简单的方法是使用两个定位销钉。定位销钉可以是位于副镜框底部环上的一对1 / 4-20托架螺栓，它们间隔180°，长度足以穿过连接环上的匹配孔。将销钉永久固定在副镜框上。每次安装望远镜时，将两个螺栓对准连接环上的孔，这样望远镜的光轴校准也就有保证了。
To prevent the connecting ring from scuffing the bottom ring of the secondary cage, put four ordinary plastic chair glides equally spaced around the bottom of the secondary cage. Chair glides are about 1/4 inch thick, and they act as spacers to provide clearance for the screw heads that connect to the struts between the secondary cage and the connecting ring.
为了防止连接环磨损副镜框的底环，请在副镜框底部均匀放置四个椅子地脚钉。椅子地脚钉大约1/4英寸厚，它们起到垫片的作用，在副镜框和连接环之间，为固定支柱的螺钉头提供间隙。
Locate the spacers as close to the latches and truss pole tips as possible, preferably directly underneath. If you don't place them close enough, the rings will bend and warp towards one another as the latches are drawn tight。If the top of the secondary cage is 12 o'clock, mount the two hooks that it hangs on at 11 and 1 o'clock. (The focuser is at 9 o'clock). Attach the tie-down rope at 6 o'clock.
找到尽可能靠近扣锁和桁架顶点的位置垫片，最好直接放在其下面。否则，如果垫片和锁扣距离太远，随着扣锁被拉紧，环可能会出现翘曲。如果副镜框的顶部是12点钟，则将挂在其上的两个挂钩安装在11和 1点位置。（调焦座在9点钟位置）。 在6点钟位置系安全绳。
6.4 Install the Hardware
安装硬件
Although your secondary cage is nearly complete, you may want to postpone taking the final steps-adding the secondary mirror and focuser-until you are ready to determine the length of the truss tubes. The reason for waiting is that nothing bad can happen to the secondary mirror or the focuser while they are sitting safely in their boxes—so let them sit. Only when you are ready to put them into service should you expose dent to the dangers of fingerprints, curious children, and accidental falls to the floor.
尽管此时副镜框几乎完成，但安装副镜和调焦座这两个步骤，建议推迟到要确定桁架管的长度时再进行。推迟的原因是：把副镜或调焦座放在包装箱里是最安全的，如果提前装上，则会有留下指纹、被熊孩子破坏以及偶然摔到地上的危险。所以等到确实要用它们时再安装。
6.4.1 Install the Focuser
安装调焦座
Since you have already drilled a hole in the focuser board for the focuser, it's a snap to install. Put it in place, put bolts through the holes in the base, and it's done. Easy-in fact， too easy. To check that it is in the correct place, install the spider. Drill holes through the Kydex baffle, then push machine screws through each of the struts to engage the studs on the spider. Run in the machine screw tight enough that the spider makes a nice "twang" when you pluck the vanes.
由于你已经在调焦座安装板上钻了一个孔，所以安装调焦座很简单。把它放到位，把螺栓穿过底座上的孔，然后就完成了。这太简单了。 要检查它是否在正确的位置，就需要安装副镜架。 在Kydex遮光板上钻孔，然后将机器螺钉穿过每个支柱，与副镜架叶片末端的螺柱相连。拧紧螺钉，让副镜架的叶片拉紧，直到拨动它能听到类似琴弦的声音。
Make a dummy secondary mirror from a sheet of stiff paper. You can photocopy the special ellipse template in this book (Figure 11.2) and cut it out with scissors. The template is a 45°ellipse with a minor axis equal to the minor axis of the secondary mirror, and it has lines down the major and minor axes. If you plan to off-set the secondary, make a mark at the offset center, some small distance down the major axis of the ellipse. Install the dummy in the secondary holder with the major axis oriented so that the offset center is closer to the focuser than the true center.
用一张硬纸板做一个假的副镜。你可以复印本书中的特殊椭圆模板（图11.2）并用剪刀剪下。该模板是一个45°椭圆，短轴等于副镜的短轴，沿着长轴和短轴画有线条。 如果您打算让副镜做offset偏移，请沿着椭圆的长轴向下一小段距离标记offset中心。将假副镜安装在副镜座上，用副镜的长轴定向，使副镜的offset中心比副镜的真实中心更靠近调焦座。
Install the secondary holder in the spider hub. Be sure to leave an extra 1/4 inch between the spider hub and the holder base. Place a coarse alignment sighting tube in the focuser. The cross hairs in the sighting tube should coincide with the intersection of the major and minor axes if you do not plan to offset the secondary, or with the offset center if you are offsetting the secondary. Figure 11.10 shows how this will look to you.
将副镜座安装在副镜架上，注意留出1/4英寸的空隙。 在调焦座上放置一个简易的校准目镜。校准目镜的十字线应该与副镜中心重合（如果你不打算偏移副轴，就是与副镜的长轴和短轴的交点重合；如果你打算偏移副轴，则与offset中心重合）。 图11.10给出了详细的图示。
If you do not see perfect alignment, not to worry. This is why you left some leeway for adjustments. Move the secondary up or down the tube until the cross hairs coincide with the true center or the offset center of the dummy secondary. If the focuser board is not strictly straight. you may be able to achieve alignment by shimming the focuser. If you figured the distances correctly between shimming the focuser and shifting the secondary along the optical axis，you should see the center of the secondary neatly on the cross hairs of the coarse alignment tube.
如果此时还没有很好地校准，不用担心。 这就是为什么要留有余地进行调整的原因。 沿镜筒方向向上或向下移动副镜座，直到十字线与假副镜的真正中心或偏移中心重合。如果发现调焦座支撑板是歪的，可以通过增加垫片的方式来校准调焦座方向。如果调焦座和副镜都调好了，则应该能通过简易校准目镜看到十字线与副镜中心重合。
If the alignment error along the optical axis is greater than 1/2 inch or so，you figured something wrong, and you may need to change the position of the secondary mirror by moving the spider. Better that you found it now rather than later, but it's no fun to drill another set of holes for the spider vanes.
如果沿着望远镜光轴的校准误差大于1/2英寸左右，则可能是前面出现了计算错误，你可能需要通过移动副镜支架来改变副镜的位置。这个问题早发现比晚发现好，不过如果需要为副镜架钻另一组固定孔，总归不是好玩的事情（译者：实际有可能通过改变副镜架的安装和调节螺丝长度解决这个问题）。
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