FPL-51 vs FPL-53 vs non-ED

Astro-Physics 的 R.C 给出的一份色差对焦点的图，很有用处。用来说明玻璃材料对色差的影响。先贴上，需要的话再解释。另，关于2/3/4片的结构以及tv与ap的成像差异，他也有很好的解答呢。但是E文，需要就zt过来。

这是什么啊?

建议加精。

楼主把E文也贴过来吧，就是这段：

关于2/3/4片的结构以及tv与ap的成像差异，他也有很好的解答呢。

英文是星期天看到的，让我翻翻

直接发E文好了，翻译慢慢弄

有沒有光学數据可供分析

The Meade design used FPL51 in combination with KF3. This is a good set of glass for making fabrication easy and foolproof, especially at F9.

More expensive ED glass FPL53 does not buy you much in the way of improved color correction if the same mating element KF3 is used. The improvement is only about 10% less color, not enough to see a whole lot of difference. The internal curves change a bit, but centering is still difficult and must be done with an accurate lens cell.

FPL53 does have the potential for better color correction when used with a different mate, but I doubt that the Orion/Synta scopes have anything more than FPL53 and KF3 or similar combination. The mating elements that achieve exceptionally low color error over a wide spectrum will require some fancy lens cells and very tight centering tolerances.

There are many reasons why color correction in lenses is difficult to judge. Often it is not known over what wavelength range the correction is being measured. The attached image shows three levels of color corretcion, achromat, normal ED doublet and triplet apo. It can be seen that the normal ED doublet has pretty good correction over a fair portion of the range, but loses quite rapidly in the far violet. However, some eyes are not sensitive in the violet, so an out-of-focus halo is not seen by those people, and the color correction cannot really be judged this way.

>So the advantage of using flourite is that the mating element and required curves are somewhat forgiving when compared to FPL53 doublets?>

NO! Where did you get that idea? FPL53 and Fluorite are one and the same thing optically. With any given mating element, the curves are for all practical purposes identical.

There is no real advantage of fluorite over FPL53, and it is almost impossible to tell them apart. In fact, I have checked some of the commercial "fluorite" refractors and found no fluorite in them. The easiest way that you can tell fluorite from ED glass such as FPL53 is by shining a laser beam through the material. If you can see the beam inside the glass, it is not fluorite.

Real fluorite costs about 3 times that of FPL53, so there is every incentive for manufacturers to substitute this material for fluorite (and still claim fluorite's dubious advantages). The only advantage that fluorite has is in the UV where no amateur astronomy takes place, either visually or photographically. ED glass is very much easier to polish and handle. Unfortunatley, FPL53 ED is not available above 7 inches, so that is where fluorite may be required for high end apo systems.

[ 本帖最后由 yanbinemail 于 2007-3-21 13:30 编辑 ]

已经收藏。回家慢慢看

已经先进行了加分了，至于加精华，可能还需等等～论坛上很多人E文不是太好！所以希望有人能翻译一下～
偶E文也不咋的，尽管能看懂这段文字的大致意思！ 所以还是不做翻译丢丑了！

好把，给我10分钟，我给翻译一下。

再来：
I have designed many Petzval lenses, so it is not necessary to inform me of the particulars. The main contribution to color error in any optical system, Petzval included, occurs at the main element (the one with the biggest diameter). In the case of the Petzval, one splits the focal length between the two lenses so that the secondary lens is inserted half way down the tube. In this way, all the off-axis aberrations can be balanced to achieve a zero Petzval sum (i.e. coma, field curvature etc). I can assure you that the front objective by itself will indeed focus light on-axis just like any well corretced doublet. It will, however, have horrendous coma as you go off-axis.

Having the front lens at F11 makes the color correction infinitely easier than trying to do it at F5.5 with one full size lens set such as a doublet or triplet. One does not need as exotic a design to get excellent color correction this way. Since the rear lens is half size, and also F11, it contributes nothing to the color error.

The alignment tolerances in a Petzval are no more difficult than in any high performance apo design.

A Petzval lens has low off-axis aberrations (coma, field curvature) as well as better sphero-chromatism than a normal lens of the same focal length.

One drawback to the Petzval is the loss of light as you go farther and farther off-axis. It is inherent in the system (see attached diagram). In order to cover a 2" field with a 4" Petzval lens, the secondary element needs to be 4" diameter in order to catch all the off-axis rays. This is not done in any of the commercial lenses, including the Tak FSQ Petzval. It would be too costly to do it.

The advantage of a normal lens design is that there is no off-axis vignetting, except by the maximum size of the tube walls.

原文比对翻译太麻烦了，我还是把其中的主要意思给大家翻译出来，不对的地方敬请指正。

Meade 设计用了 FPL51 和 KF3 的组合。 这种组合使制造更加简单和安全，尤其是在F9这个焦比上。

如果使用更贵的玻璃 FPL53 和KF3组合，并不会太多的提高对颜色的纠正，这种纠正改良的作用也就是 10%左右,并且很难用肉眼查觉。 用FPL53只能对曲线改正一点点，但是中心仍然很困难，中心部分曲线的改良必须要有更加精确的透镜组合。

FPL53与其他镜片的组合确实由提升修正色差的潜能，但是我怀疑，ORION与SYNTA的望远镜使用的镜片组合超过了FPL53 和 KF3 或相似的组合的设计。他的镜子在一个宽的光谱范围内，色差表现得非常出色，这需要更加更加昂贵的透镜和非常精密的中心误差控制。

Meade的设计用了fpl51与kf3. 这是好的一个玻璃匹配，容易制造和加工和容错，尤其在f9.
如果与kf3配用,较贵的fpl53ed玻璃并不使你在改善其色彩校方面获益. 只有约10%的颜色改善,不足以看见很大差别. 内部曲面变化了一点,但是合焦仍然困难，而且必须要有精准的镜头单元.
当使用不同的玻璃组合时，fpl53的确有更好的色彩校正的潜力,但我怀疑,orion/synta使用了高于fpl53/kf3或类似的组合. 要在广谱范围内达到极低的色差，配合镜片将需要一些特别的镜头单元和极其小的中心误差.
镜片色差校正难以判断的原因是多方面的. 我们常常不知道色差校正在什么波长范围内衡量. 所附的图像文件显示三种层次的校正,普通消色差,一般2片ed和3片apo. 可见一般2片ed的色差在相当一段光谱中已经不错了, 但在紫色后很快的就偏离了. 但是,有些眼睛对紫色不敏感,所以在焦外的紫色不会被所有人看见, 色彩校正真是不能这样判断.

问：>与 fpl53相比，用萤石的好处是配合镜片以及所需曲线可以有所放宽？>
答：不! 你在那里得到这想法? fpl53同萤石在光学方面是相同的.在给定了配合镜片的情况下,实际上讲曲线是一致的.
实际上萤石对fpl53没有真正的优势,而且它们几乎是不可能区分的. 事实上,我曾检查过一些商业"萤石"折射镜但在里面没有找到萤石. 简单的方法可以告诉你，从fpl53等ed玻璃中区分出萤石可以用激光照射. 如果你能看到玻璃内的光束,就不是萤石.
萤石真实成本约是fpl53的3倍, 所以这一切促使厂商替代萤石材料(但还会称有萤石的优良特性). 萤石唯一的好处是在紫外光波段，但无业余天文学者涉及,不论是视觉或照片. ed玻璃很容易处理和抛光. 不幸的是,找不到7英寸以上的fpl53, 而这是高端apo系统可能需要萤石的地方.

[ 本帖最后由 yanbinemail 于 2007-3-21 15:03 编辑 ]

后面麻烦楼主也翻译一下吧，呵呵，懒着动弹了

我设计过有很多Petzval镜头,因此没有必要通知我. 任何光学系统在控制色差方面的主要贡献,包括Petzval，是发生在主镜单元(其中直径最大的那组). 对于Petzval的情况、 一组镜片将两组镜片之间的焦距改变而第二组镜头要在镜筒的中部放入. 这样一来,所有的离轴像差可达到平衡，即Petzval累计零(即彗差，场曲等). 我可以向你保证,实际上前面的物镜实本身将光线聚到光轴上，就像任何好2片镜头一样. 然而,它将有可怕的离轴彗差.
与使用f5.5的全口径2片镜头或3片镜头相比，在前面用个F11的镜头使得色彩校正变得极其容易得多.我们不需要设计一个异常出色的色彩校正. 由于后方镜头只有一半大小,也是F11,它不会增加更多色差.
Petzval的校正误差不比高性能的apo难.
一个Petzval镜头比相同焦距的透镜具有低离轴像差(彗差，场曲)以及较好的球色差.
Petzval的美中不足的是你离轴越远光线损失越大. 它是系统固有的属性(见附图). 为了用4寸的Petzval镜头覆盖一个2寸的像场，第二组镜片的直径必须为4寸，才能抓住一切离轴光线. 任何商业镜头都做不到这一点，包括tak的Petzval. 这样便太昂贵.
正常镜片设计优势就是没有离轴昏晕,除了使用最大尺寸的管壁.

[ 本帖最后由 yanbinemail 于 2007-3-21 15:06 编辑 ]

支持一个。

好文

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今晚很 HI