加载中…
普消 vs ED三片
(2007-09-10 22:26:40)
标签：
知识/探索普消ed三片天文器材 |
分类： 天文基础知识 |
转自牧夫论坛
翻译：yanbinemail
ed一词可能意味着它完全更正各级可见光波长的色差.
不过ed根本不意味任何校正.ed玻璃可以用来纠正色差,但是不是仅仅靠它.
完全的色彩校正来自ed玻璃与冕牌玻璃的组合,无论双片还是三片. 如果ed结合火石玻璃或冕牌-火石玻璃或其他类似型号你会有或多或少的色差.只有冕牌玻璃搭配才能实现波长较广范围内真正的apo.
为什么ed玻璃生产厂家使用火石或冕牌-火石而不是理想的冕牌玻璃? 毕竟,一个冕牌玻璃是纯净、清晰、较难生纹并比任何火石或冕牌-火石玻璃便宜. 他们这样做是为了实现短焦并没有严重的球差,或保持成本,因为火石玻璃制造容易误差宽松. 当你用冕牌玻璃与ed搭配,误差精确程度须高达10倍,但这样做的可达到色彩校正可以好10倍之多.
两种玻璃（fpl51, fpl53）都可进行适合组合来制造矫正优异的透镜组. 这只是可达到焦比的问题.
要达到零色差的透镜,2片的fpl51须约在f15左右，3片6"就要f8的样子. 2片的fpl53须约在f12左右，3片就要f6的样子才能做到零色差.fpl52介于两者之间. 萤石会类似于fpl53那样在最小可达到焦比方面.
如果不需要色差为零, 那么用任何上述的东西都可以做出不同矫正程度的2片组合. 我相信对于相同的色差,2片的fpl53在F7将类似于F9的fpl51双片. 因此,你知道这未必是某一种颜色较少,而对于任何具体程度的颜色，一种须长于另一类型.
厂商依据性价比选择校正方式。允许更多色差通常降低了成本,但到某个程度后会白干. 用便宜的ed努力实现零色差会大幅提高价格因为匹配玻璃变得昂贵，而且制作难度变得很大.这将成为一件在性价比范围里将所有这些事的变数合计去达到某种方案.
于是厂商会尝试各种方法,看看它如何获得客户.有时简单地削减一点口径并保持焦距就可以成就一个最佳公式. 比如个85毫米f6.4可能按某定公式做太难了,但去掉口径到72毫米f7.5，就很有成本效益(对所有的制造商来说最好大多数人不会看到口径的不同).
优胜者可以在各种类型中发现，从最低的性价比到最高成本和最高性能的类型
这段是我总结的，他的原话太长。
下面的图是比较普消与3片ed的理论成像，可以看到普消得兰/紫色很重。但是，如果我们仅仅对比绿色的图像，两种镜子的结果是一样的！不信就在photoshop里只看绿色通道，看看木星的细节有没有区别。
完全的色彩校正来自ed玻璃与冕牌玻璃的组合,无论双片还是三片. 如果ed结合火石玻璃或冕牌-火石玻璃或其他类似型号你会有或多或少的色差.只有冕牌玻璃搭配才能实现波长较广范围内真正的apo.
为什么ed玻璃生产厂家使用火石或冕牌-火石而不是理想的冕牌玻璃? 毕竟,一个冕牌玻璃是纯净、清晰、较难生纹并比任何火石或冕牌-火石玻璃便宜. 他们这样做是为了实现短焦并没有严重的球差,或保持成本,因为火石玻璃制造容易误差宽松. 当你用冕牌玻璃与ed搭配,误差精确程度须高达10倍,但这样做的可达到色彩校正可以好10倍之多.
两种玻璃（fpl51, fpl53）都可进行适合组合来制造矫正优异的透镜组. 这只是可达到焦比的问题.
要达到零色差的透镜,2片的fpl51须约在f15左右，3片6"就要f8的样子. 2片的fpl53须约在f12左右，3片就要f6的样子才能做到零色差.fpl52介于两者之间. 萤石会类似于fpl53那样在最小可达到焦比方面.
如果不需要色差为零, 那么用任何上述的东西都可以做出不同矫正程度的2片组合. 我相信对于相同的色差,2片的fpl53在F7将类似于F9的fpl51双片. 因此,你知道这未必是某一种颜色较少,而对于任何具体程度的颜色，一种须长于另一类型.
厂商依据性价比选择校正方式。允许更多色差通常降低了成本,但到某个程度后会白干. 用便宜的ed努力实现零色差会大幅提高价格因为匹配玻璃变得昂贵，而且制作难度变得很大.这将成为一件在性价比范围里将所有这些事的变数合计去达到某种方案.
于是厂商会尝试各种方法,看看它如何获得客户.有时简单地削减一点口径并保持焦距就可以成就一个最佳公式. 比如个85毫米f6.4可能按某定公式做太难了,但去掉口径到72毫米f7.5，就很有成本效益(对所有的制造商来说最好大多数人不会看到口径的不同).
优胜者可以在各种类型中发现，从最低的性价比到最高成本和最高性能的类型
这段是我总结的，他的原话太长。
下面的图是比较普消与3片ed的理论成像，可以看到普消得兰/紫色很重。但是，如果我们仅仅对比绿色的图像，两种镜子的结果是一样的！不信就在photoshop里只看绿色通道，看看木星的细节有没有区别。
附上原文
The term ED might imply
that it is fully corrected for color error at all visible
wavelengths. However ED does not mean anything about correction at
all. ED glass CAN be used to correct color error, but does not
necessarily do so on its own.
Full color correction comes from a combination of ED glass and crown glass, either in doublet or triplet configuration. If ED glass is combined with Flint glass or Crown-Flint or other similar types, you will have more or less color error. Only crown glass mates can achieve true apo performance over a wide wavelength range.
Why do manufaturers use ED glass with flint or crown-flint and not the ideal crown glasses? After all, a crown glass is actually purer, clearer, less prone to striae and less costly than any crown-flint or flint glass. They do this to achieve fast focal ratios without messy aspherization, or to keep the cost of fabrication down because flint glass makes for easy manufacturing and looser tolerances. The tolerance level will need to be as much as 10 times tighter when you use a crown mate with ED glass, but the color correction achieveable this way can be as much as 10 times better.
Either glass can be combined with suitable mate to produce a highly corrected lens. It's just a matter of focal ratio achievable.
For a zero color lens, FPL51 would need to be about F15 in a doublet, F8-ish for a triplet in a 6" size. FPL53 would need to be about F12 for a doublet, F6-ish for a zero color lens. FPL52 lies somewhere in between. Fluorite would be similar to FPL53 in min achieveable focal ratio.
If zero color is not required, then doublets of various amount of correction can be made with any of the above. I would say that for the same color error, FPL53 at F7 would be similar to FPL51 at F9 in a doublet. So, you see it is not necessarily that one has less color, rather for any specific amount of color, one type of ED would need to be longer than another type.
The manufacturer makes the choice of correction based on cost/performance. Allowing more color error usually lowers the cost, but at some point this flattens out. Trying to achieve zero color with the cheaper ED glass can actually increase the price dramatically because the mating element becomes expensive, and the fabrication difficulty becomes enormous. It becomes a matter of putting all these variables together to achieve a certain result in the cost/performance spectrum.
Therefore manufacturers will try various approaches to see how it is received by the audience. Sometimes it is a simple matter of dropping the aperture down a few notches and keeping the focal length the same that can produce a winning formula. For instance, an 85mm F6.4 might be too difficult to make with a certain formula, but by dropping the size down to 72mm F7.5, it becomes cost effective (best of all for the manufacturer, most people won't perceive a difference in aperture).
Winners can be found in all categories from the least cost/performance to the highest cost and highest performance models.
Full color correction comes from a combination of ED glass and crown glass, either in doublet or triplet configuration. If ED glass is combined with Flint glass or Crown-Flint or other similar types, you will have more or less color error. Only crown glass mates can achieve true apo performance over a wide wavelength range.
Why do manufaturers use ED glass with flint or crown-flint and not the ideal crown glasses? After all, a crown glass is actually purer, clearer, less prone to striae and less costly than any crown-flint or flint glass. They do this to achieve fast focal ratios without messy aspherization, or to keep the cost of fabrication down because flint glass makes for easy manufacturing and looser tolerances. The tolerance level will need to be as much as 10 times tighter when you use a crown mate with ED glass, but the color correction achieveable this way can be as much as 10 times better.
Either glass can be combined with suitable mate to produce a highly corrected lens. It's just a matter of focal ratio achievable.
For a zero color lens, FPL51 would need to be about F15 in a doublet, F8-ish for a triplet in a 6" size. FPL53 would need to be about F12 for a doublet, F6-ish for a zero color lens. FPL52 lies somewhere in between. Fluorite would be similar to FPL53 in min achieveable focal ratio.
If zero color is not required, then doublets of various amount of correction can be made with any of the above. I would say that for the same color error, FPL53 at F7 would be similar to FPL51 at F9 in a doublet. So, you see it is not necessarily that one has less color, rather for any specific amount of color, one type of ED would need to be longer than another type.
The manufacturer makes the choice of correction based on cost/performance. Allowing more color error usually lowers the cost, but at some point this flattens out. Trying to achieve zero color with the cheaper ED glass can actually increase the price dramatically because the mating element becomes expensive, and the fabrication difficulty becomes enormous. It becomes a matter of putting all these variables together to achieve a certain result in the cost/performance spectrum.
Therefore manufacturers will try various approaches to see how it is received by the audience. Sometimes it is a simple matter of dropping the aperture down a few notches and keeping the focal length the same that can produce a winning formula. For instance, an 85mm F6.4 might be too difficult to make with a certain formula, but by dropping the size down to 72mm F7.5, it becomes cost effective (best of all for the manufacturer, most people won't perceive a difference in aperture).
Winners can be found in all categories from the least cost/performance to the highest cost and highest performance models.
喜欢
0
赠金笔