0.8米牛顿反射镜前端 Front End of the 0.8 m Newtonian Reflector
分类: 器材 Equipment, 器材情报 Equipment, 技术项目 Projects
2026-01-27
0.8米反射镜前端 - 彗差镜及调焦副镜保护 Front End of the 0.8 m Reflector – Coma Corrector and Focuser/Mirror Protection
反射镜好玩的地方是很多发挥改良空间，也能实现很个人风格，大口径反射镜因为没有现成产品，自己动手是乐趣又能省不少钱。
这里分享两点，
1. 因为是f/3极短焦牛顿反射镜，要全时间用上Televue的Parcorr彗差修正镜，能实现在26mm直径，即我用的最长Ethos 21目镜像场的70%，逹到绕射极限(diffraction limited)。这修正镜是SIPS系统，即跟羽毛调焦融而为一的系统，要求放置在指定后焦点(back focus)位置才可发挥功效，结果来回4个位置都试完了才找到一个最合适的连接方法。
2. 从伟大的某宝买了一个廿多元的18公升水桶来保盖这片21x30公分副镜，再花几元买个胶盒来盖调焦座及彗差镜，简单又实用，但连日来被不只一个朋友笑这个够粗犷(就不能叫豪迈吗?)，因为羽毛调焦的金色慢速钮那位置的转轴很幼细，不小心一撞便要花上百美元返厰维修，所以还是保护一下较好。
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.
反射镜好玩的地方是很多发挥改良空间，也能实现很个人风格，大口径反射镜因为没有现成产品，自己动手是乐趣又能省不少钱。
这里分享两点，
1. 因为是f/3极短焦牛顿反射镜，要全时间用上Televue的Parcorr彗差修正镜，能实现在26mm直径，即我用的最长Ethos 21目镜像场的70%，逹到绕射极限(diffraction limited)。这修正镜是SIPS系统，即跟羽毛调焦融而为一的系统，要求放置在指定后焦点(back focus)位置才可发挥功效，结果来回4个位置都试完了才找到一个最合适的连接方法。
2. 从伟大的某宝买了一个廿多元的18公升水桶来保盖这片21x30公分副镜，再花几元买个胶盒来盖调焦座及彗差镜，简单又实用，但连日来被不只一个朋友笑这个够粗犷(就不能叫豪迈吗?)，因为羽毛调焦的金色慢速钮那位置的转轴很幼细，不小心一撞便要花上百美元返厰维修，所以还是保护一下较好。
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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