歡迎討論

[LT]

上一貼文說過30cm牛牛身體抱恙，下圖是其中一病。

歡迎討論是什麼原因導致這樣怪怪的副鏡支架繞射圖形(diffraction pattern)？

[Wah!!]

我估:
1. 副鏡架是十字, 其中一對是直線, 另一對不再直線, 有小小角度.
2. 光路上有其他直線的東東產生第三條光芒.

最好發張望遠鏡相來睇下.

[Carl Chan]

我估:
1. 副鏡架是十字, 其中一對是直線, 另一對不再直線, 有小小角度.
2. 光路上有其他直線的東東產生第三條光芒.

最好發張望遠鏡相來睇下.

同意

[A/45]

Agree.
Please check if the four spiders are precisely 90 deg. apart; also, see if there are screws sticking out from the secondary holder or tube rim.

[LT]

相信Wah已說對原因了。

按計算，要得到最大的100%照亮直徑，副鏡要offset 5mm左右。故為了方便和較準確調校這個 offset 量，故 offset 副鏡支架中心 5mm。這個 offset量真的很大，副鏡支架不能再近似90度形狀，變成了一個近似的Bahtinov mask！

現在只有再做另一個支架。

[A/45]

What I've tried before was to re-glue the secondary mirror onto the secondary holder so that only the mirror is offset, rather than to alter the spiders and the secondary holder.
Therefore the centre of the secondary mirror is vertically 5mm away from centre of the spiders and holder.

[LT]

No, position of the secondary mirror cannot be re-glued as the diameter of the secondary mirror holder = M.A. of secondary mirror. So, it is better to make another spider for my case.