親子觀星會

牛頓 望遠鏡副鏡支架和星芒

https://www.facebook.com/photo.php?fbid=1769862139693525&set=gm.1646876358702521&type=3&theater


很多 SCt 前面是透明的 .
但是牛頓鏡 .  meade 出過透明牛頓 望遠鏡副鏡支架 ?

WIKI
https://zh.wikipedia.org/wiki/%E7%89%9B%E9%A1%BF%E6%9C%9B%E8%BF%9C%E9%95%9C


    第二反射鏡在光路的中間，會遮蔽掉部分的光線，支撐結構還會造成繞射形成所謂的蜘蛛網，並且降低對比。使用二或三支腳的支撐可以減少視覺上的蜘蛛網。減少繞射的肩峰值強度更可以以四的因次有效的增強對比，
但圓形的蜘蛛網通常是因支撐不穩，而由風造成擺動形成的懲罰。
雖然四隻腳的支撐能比三隻腳更有效的消除蜘蛛網，但三支腳造成的蜘蛛網會給人一種審美上的良好觀感。

    可攜式牛頓式的校準是個問題。主鏡和次鏡的準直性會因為運輸和操作時的震動而偏離，
這意味著望遠鏡可能在每次使用前都需要校準。其他型式的設計，
像折光鏡和折反射鏡（尤其是馬克蘇托夫蓋塞格林式），準直性都已經固定住了。

Newtonians have a central obstruction due to the secondary mirror in the light path. This obstruction and also the diffraction spikes caused by the support structure (called the spider) of the secondary mirror reduce contrast. Visually, these effects can be reduced by using a two or three-legged curved spider. This reduces the diffraction sidelobe intensities by a factor of about four and helps to improve image contrast, with the potential penalty that circular spiders are more prone to wind-induced vibration.

https://en.wikipedia.org/wiki/Diffraction_spike
(https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Newtonianscope-inside.JPG/330px-Newtonianscope-inside.JPG)

(https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/Comparison_aperture_diffraction_spikes.svg/600px-Comparison_aperture_diffraction_spikes.svg.png)


Comparison of diffraction spikes for apertures of different shapes and blade count

https://www.facebook.com/photo.php?fbid=1791062947572168&set=p.1791062947572168&type=3&theater
https://www.facebook.com/photo.php?fbid=2096183300408921&set=p.2096183300408921&type=3&theater

(https://scontent.ftpe8-3.fna.fbcdn.net/v/t1.0-9/27337196_1791062947572168_1617186634540326058_n.jpg?oh=6d42dd381580928f92e2831a85397f6d&oe=5AE48BA1)

(https://scontent.ftpe8-3.fna.fbcdn.net/v/t1.0-9/26992738_2096183300408921_2496647496811360140_n.jpg?oh=fcb0c855e6758025e9fc7926a77b1a38&oe=5AE0CFFF)

MEADE   Schmidt-Newtonian ...

https://en.wikipedia.org/wiki/Schmidt%E2%80%93Newton_telescope

https://starizona.com/acb/basics/equip_telescopes_schmidtnewt.aspx

(https://starizona.com/acb/basics/optics/schmidtnewt_scope.jpg)


Maksutov-Newtonian
(https://starizona.com/acb/basics/optics/maknewt_scope.jpg)

http://wtamu.edu/~cbaird/sq/2015/11/16/why-do-the-spikes-that-shoot-out-of-stars-form-perfect-crosses/

http://www.astrosurf.com/viladrich/astro/instrument/sensitivity/spider-diffraction.htm


https://www.cloudynights.com/topic/495707-spider-and-secondary-diffraction-what-to-do-what-to-avoid/

https://www.cloudynights.com/topic/589406-why-are-my-diffraction-spikes-offsetmisaligned/

http://www.fpi-protostar.com/cm-faq.htm

(http://www.fpi-protostar.com/img/spikes.gif)

https://blogs.stsci.edu/newsletter/2013/09/26/staying-sharp-keeping-hubble-and-webb-seeing-clearly/
HST 也是十字狀的

(https://blogs.stsci.edu/newsletter/files/2013/09/OPTICS-1-300x259.jpg)

TS 又換了 台望遠鏡
 12.5" DOB

https://www.facebook.com/photo.php?fbid=2244402345573799&set=p.2244402345573799&type=3&theater


https://www.facebook.com/photo.php?fbid=2243897108957656&set=pcb.2243897758957591&type=3&theater
(https://scontent.ftpe8-4.fna.fbcdn.net/v/t1.0-9/28661399_2243897115624322_7712744292669718528_n.jpg?oh=25805cdb7f80097401504cc24913fb28&oe=5B088EFA)

(https://scontent.ftpe8-4.fna.fbcdn.net/v/t1.0-9/28870566_2244390495574984_7759951717034098688_n.jpg?oh=16c1a3bb1453768b8aa75290376ff143&oe=5B076E3E)
(https://scontent.ftpe8-4.fna.fbcdn.net/v/t1.0-9/28871914_2244402348907132_1363397261710589952_n.jpg?oh=1858e2d04c3e842221d8d8d971377340&oe=5B0C7F0F)

https://stargazerslounge.com/topic/305665-strange-diffraction-spikes/

https://www.cloudynights.com/topic/552489-whats-causing-this-spike-in-my-sct-image/

CORSS LINK

http://familystar.org.tw/index.php?option=com_smf&Itemid=35&topic=19850.msg242489#msg242489

TED

https://www.facebook.com/photo?fbid=5540988489248485&set=pcb.5541014309245903

TELESCOPE secondary mirror holder 

https://www.cloudynights.com/topic/498372-cheap-torsionally-stabilized-four-vane-secondary-mirror-spider/

torsionally-stabilized four-vane secondary mirror spider
(https://www.cloudynights.com/uploads/monthly_04_2015/post-217011-0-19341400-1429957161.png)

https://www.youtube.com/watch?v=Ft8CMEooBAE 


The simulations were done using the Angular Spectrum Method implemented with Python.
You can find the Source Code here:
https://github.com/rafael-fuente/diffractsim

WEBB

https://familystar.org.tw/index.php?option=com_smf&Itemid=45&topic=23509.120

https://www.youtube.com/watch?v=4IH2boJFshU

http://www.astrosurf.com/viladrich/astro/instrument/sensitivity/spider-diffraction.htm

https://technews.tw/2022/03/21/diffraction-spike-webb-space-telescope-jwst/ 

專家解釋這是當初設計韋伯望遠鏡的一個功能，當星光進入主鏡後略為偏轉產生繞射，最終可形成稱為繞射尖光的放射狀光芒，有助於證實各分割鏡面已完美排列。

德州農工大學物理學系助理教授 Christopher S. Baird 表示，韋伯望遠鏡成像產生繞射尖光（Diffraction spike）的關鍵在於輔助鏡通過支撐桿固定在主鏡上方，這些支撐桿會阻擋入射光，當星光進入望遠鏡主鏡時，其中一些光掠過支撐桿並略微偏轉產生繞射，最後在成像中形成沿著支撐杆延伸的放射狀光線。

不過繞射也可能由望遠鏡鏡面邊緣引起，歐洲太空總署天文學家 Mark McCaughrean 解釋，尖光結構是設計韋伯望遠鏡主鏡的功能之一， 18 個六邊形分割鏡面都印有微弱繞射圖案，可恆星光芒看起來像雪花──對科學研究來說不成問題，還能帶來非常獨特的外觀。

事實上相關設計在地面望遠鏡中很常見，包括凱克望遠鏡、加那利大型望遠鏡（GTC）、霍比-埃伯利望遠鏡（HET）、南非大望遠鏡（SALT）、中國郭守敬望遠鏡（LAMOST）等，但韋伯望遠鏡是第一個納入這種設計的太空望遠鏡。

https://bigthink.com/starts-with-a-bang/james-webb-spikes/

(https://bigthink.com/wp-content/uploads/2022/03/FOFC8ZPX0AIB-Ho.png?resize=768,346)

Simulating spider diffraction


TOOLS
https://familystar.org.tw/index.php?option=com_smf&Itemid=45&topic=36292.0


http://www.njnoordhoek.com/?p=376

JWST

https://www.facebook.com/photo/?fbid=4866495776800723&set=pcb.4866394893477478

日本  用於 Dobsonian  卡塞格林的 星芒

口径250ｍｍニュートン（ドブソニアン）カセグレン専用バイナリー・ホトグラフ・アポタイザー★STARWORKS　

劉志安分享了 1 則貼文。
 
圖解說明 韋伯望遠鏡六長兩短繞射星芒形成的原因~
https://www.facebook.com/groups/TAiIPEIAAA/posts/5433162680074405

https://www.telescope-optics.net/spider.htm

FWMH
=>  https://familystar.org.tw/index.php?option=com_smf&Itemid=45&topic=37727.msg257728#msg257728

https://www.facebook.com/photo/?fbid=646971407435107&set=pcb.646978024101112

可以3d印表機 印特別的圖，套折射鏡前去故意產生 特別星芒