0.8米牛頓反射鏡前端 Front End of the 0.8 m Newtonian Reflector
分類: 器材 Equipment, 器材情報 Equipment, 技術項目 Projects
2026-01-27
0.8米反射鏡前端 - 彗差鏡及調焦副鏡保護 Front End of the 0.8 m Reflector – Coma Corrector and Focuser/Mirror Protection
反射鏡好玩的地方是很多發揮改良空間，也能實現很個人風格，大口徑反射鏡因為沒有現成產品，自己動手是樂趣又能省不少錢。
這裡分享兩點，
1. 因為是f/3極短焦牛頓反射鏡，要全時間用上Televue的Parcorr彗差修正鏡，能實現在26mm直徑，即我用的最長Ethos 21目鏡像場的70%，逹到繞射極限(diffraction limited)。這修正鏡是SIPS系統，即跟羽毛調焦融而為一的系統，要求放置在指定後焦點(back focus)位置才可發揮功效，結果來回4個位置都試完了才找到一個最合適的連接方法。
2. 從偉大的某寶買了一個廿多元的18公升水桶來保蓋這片21x30公分副鏡，再花幾元買個膠盒來蓋調焦座及彗差鏡，簡單又實用，但連日來被不只一個朋友笑這個夠粗獷(就不能叫豪邁嗎?)，因為羽毛調焦的金色慢速鈕那位置的轉軸很幼細，不小心一撞便要花上百美元返厰維修，所以還是保護一下較好。
One of the fun things about reflecting telescopes is how much room there is for customization and improvement — it’s a great way to build something with personal character. Large‑aperture reflectors don’t come as ready‑made products, so doing the work yourself is both enjoyable and saves a lot of money.
Here I’ll share two points:
1. Since this is an f/3 ultra‑fast Newtonian, it needs to use the TeleVue Paracorr coma corrector at all times. With it properly set up, the system achieves diffraction‑limited performance across about 70 % of the 26 mm field diameter — essentially the usable field in my longest‑focal‑length eyepiece, the Ethos 21 mm. This particular corrector is the SIPS system, in which the Paracorr is integrated with a Feather Touch focuser. To perform properly, the unit must sit at the specified back‑focus position. I ended up testing four different connection configurations before finding the one that gave perfect alignment and focus.
反射鏡好玩的地方是很多發揮改良空間，也能實現很個人風格，大口徑反射鏡因為沒有現成產品，自己動手是樂趣又能省不少錢。
這裡分享兩點，
1. 因為是f/3極短焦牛頓反射鏡，要全時間用上Televue的Parcorr彗差修正鏡，能實現在26mm直徑，即我用的最長Ethos 21目鏡像場的70%，逹到繞射極限(diffraction limited)。這修正鏡是SIPS系統，即跟羽毛調焦融而為一的系統，要求放置在指定後焦點(back focus)位置才可發揮功效，結果來回4個位置都試完了才找到一個最合適的連接方法。
2. 從偉大的某寶買了一個廿多元的18公升水桶來保蓋這片21x30公分副鏡，再花幾元買個膠盒來蓋調焦座及彗差鏡，簡單又實用，但連日來被不只一個朋友笑這個夠粗獷(就不能叫豪邁嗎?)，因為羽毛調焦的金色慢速鈕那位置的轉軸很幼細，不小心一撞便要花上百美元返厰維修，所以還是保護一下較好。
One of the fun things about reflecting telescopes is how much room there is for customization and improvement — it’s a great way to build something with personal character. Large‑aperture reflectors don’t come as ready‑made products, so doing the work yourself is both enjoyable and saves a lot of money.
Here I’ll share two points:
1. Since this is an f/3 ultra‑fast Newtonian, it needs to use the TeleVue Paracorr coma corrector at all times. With it properly set up, the system achieves diffraction‑limited performance across about 70 % of the 26 mm field diameter — essentially the usable field in my longest‑focal‑length eyepiece, the Ethos 21 mm. This particular corrector is the SIPS system, in which the Paracorr is integrated with a Feather Touch focuser. To perform properly, the unit must sit at the specified back‑focus position. I ended up testing four different connection configurations before finding the one that gave perfect alignment and focus.
2. For protection, I bought a HKD 25, 18‑liter plastic water bucket on Taobao to cover the secondary mirror (210 × 300 mm), and spent a few more dollars on a small plastic box to cover the focuser and coma corrector. Simple and practical — though more than one friend has laughed at how "rough” it looks (can’t we just call it bold?). But in truth, it’s necessary: the Feather Touch focuser’s golden fine‑focus knob shaft is very slender — a single accidental bump could send it back to the factory and cost several hundred US dollars in repairs. So a bit of extra protection is well worth it!
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