本帖最后由 paraview 于 2024-4-10 23:24 编辑
不好意思我翻译的太烂了。我就直接贴英语吧，概念是Vic Menard (https://www.vicmenard.com/telescopes/) 和Nils Carlin (发明barlowed laser collimation的人，http://carlin.udjat.nl/kolli/kolli.html) 提出的。简言之就是清晰像的主轴要与目镜的镜片中心尽量重合。下面是Vic Menard的解释 ，其著作《The fifth edition of New Perspectives on Newtonian Collimation》的目录和前言见附件。
"The allowable "high magnification" focuser axial alignment error tolerance (注：一般叫FAE，without coma correction) that you quoted is mine--Nils Olof Carlin originally proposed 0.04D--actually L/(25*F), where L is the focal length and F is the focal ratio. The goal for the tolerance was to keep the defocusing contribution to 1/10 wave where the coma contribution was 1/4 wave (at the coma "free" field radius). I pushed for the slightly tighter tolerance (0.03D), as 0.04D would overwhelm an autocollimator read and even 0.03D is easily improved upon by most users, even those with minimal expertise. And I still get some heat from some of the heavy hitters in this forum for not pushing harder. Nevertheless, I regularly quote both 0.03D and 0.04D, especially for users who depend on collimation caps or sloppy lasers to assess and correct the focuser axial alignment. shrug.gif
The allowable "high magnification" primary mirror axial alignment error tolerance has been around for some time now, but it still depends on whose definition of the coma "free" field radius you choose. Roger Sinnott proposed 0.009mm times the focal ratio cubed, while Edgar Everhart proposed 0.011mm times the focal ratio cubed. For the actual allowable error tolerance, most agree that 1/2 of the coma "free" radius is valid for most high magnification applications, although 1/3 of the coma "free" radius may be useful for a dedicated "planetary" Newtonian (according to Nils Olof). The goal, of course, is to keep the coma "free" diameter (aka, the "sweet spot") centered in the eyepiece field stop.
"
另外
Q: How does a coma corrector affect the tolerances?
A: It directly affects the focuser axial tolerances, for example:
No CC--0.03D
Paracorr Type I--0.03D/6=0.005D
Paracorr Type II--0.03D/15=0.002D
It's why, if you do the numbers, an autocollimator is essential if a CC is used--it's the only tool capable of resolving errors that small.
所以，8寸10寸f6牛反不需要慧差修正，tolerance (主镜光轴可以多偏) 分别是6mm和7.5mm。大口径快镜的tolerance很可能会在1mm甚至更低，这种精度要求远超过了普通调光轴方法的能力（比如，想象一下要在调焦座达到1mm误差，用激光找主镜中心得要多准），所以这些人才发展了相应的高精度调光轴方法。
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