香港最大的 0.8 米（32 吋）反射镜开光记 - 目视猎户座大星云的碧绿与绯红 Commissioning Hong Kong’s Largest 0.8 m (32‑inch) Reflector - First Light Observations of the Orion Nebula’s Emerald Green and Crimson Glow

由于工作繁忙，主镜运抵香港已近两年，镜筒组件也躺了一年多。直到昨晚终于把镜运到城门河畔正式开光。几点小分享如下，

- 这镜焦距为2400mm f/3，配上Starlight Instruments Feather Touch调焦座及内置的TeleVue Paracorr II（SIPS），合成焦距 2760 mm。

- 搭配 100 度像场的 TeleVue Ethos 21 目镜观测时，放大率约 130 倍，实际视场为相当理想的 0.75 度，出射瞳孔为 6 mm，正好是中年观星者视觉的上限。

- 寻星镜使用 Askar 30 mm 导星镜配 Meade 25 mm 标靶目镜，机械结构十分穏固，对准目标既方便又可靠，能确保天体落在 Ethos 21 的视场之内。

- 观测猎户座大星云时，碧绿色云气格外鲜明，细心观察也可略暗的绯红，照片为手持手机拍摄，这是小口径望远镜难以企及的色彩层次，甚至大多数爱好者从没见过星云的颜色。

- 木星与四颗伽里略卫星排成一线，木星表面两条云带色彩饱和，只可惜光轴因为小技术问题尚未完全精调，因此其他行星的细节仍受限，只算中口径望远镜水平。

- 镜筒结构扎实，光轴调校相当便利。搬运与装拆虽需些许功夫，但目前仍可收纳于 Tesla Model Y 后座与尾厢内，司机仍能多载一位乘客，会再进一步优化设计。

- 台架采用 OnStep 控制系统，仍需时间熟习其操作与自动导向功能。

未来一段日子会持续优化这镜，提升使用效率。并会在观星活动中服务。

方社长

Because of a busy work schedule, the primary mirror had been sitting in Hong Kong for almost two years, and the optical tube assembly for more than one. It was only last night that the telescope was finally brought to the banks of the Shing Mun River for its long‑awaited first light. A few notes from that evening follow:

- The telescope has a focal length of 2400 mm at f/3, equipped with a Starlight Instruments Feather Touch focuser and a built‑in TeleVue Paracorr II (SIPS), giving an effective focal length of 2760 mm.

- With a TeleVue Ethos 21 mm eyepiece, offering a 100‑degree apparent field, the system provides about 130× magnification, yielding an actual field of view of roughly 0.75 degrees. The 6 mm exit pupil is just about the upper limit for middle‑aged eyes.

- The finder consists of an Askar 30 mm guide scope paired with a Meade 25 mm illuminated reticle eyepiece. The mechanical setup is solid and makes target acquisition straightforward and dependable, ensuring that the object is centered within the Ethos 21 field.

- When observing the Orion Nebula, the emerald‑green glow of the gas was strikingly vivid, with careful scrutiny revealing a faint blush of crimson, colors impossible to detect in smaller telescopes and unseen by most observers. The accompanying photo was taken handheld with a smartphone.

Jupiter and its four Galilean moons lined up neatly, with the planet’s two main belts appearing richly colored and saturated. Unfortunately, a minor collimation issue prevented perfect alignment, limiting the fine planetary detail to roughly mid‑aperture performance.

The optical tube feels robust, and the collimation mechanism is convenient and precise. Setup and transport require some effort, but the telescope still fits into the rear seats and trunk of a Tesla Model Y, leaving space for the driver plus one passenger. Further refinement is planned.

The mount runs on the OnStep control system, which will take some time to master fully, especially for automated tracking and guiding.

Over the coming months, I’ll continue to fine‑tune and optimize this 0.8 m instrument, improving both performance and handling efficiency, and it will be put to service in upcoming stargazing sessions.

Director Savio Fong