牛頓 望遠鏡副鏡支架 和星芒

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peter:
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





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

peter:
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

peter:
MEADE   Schmidt-Newtonian ...

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

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




Maksutov-Newtonian

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

peter:
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/

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