香港最大的 0.8 米（32 吋）反射鏡開光記 - 目視獵戶座大星雲的碧綠與緋紅 Commissioning Hong Kong’s Largest 0.8 m (32‑inch) Reflector - First Light Observations of the Orion Nebula’s Emerald Green and Crimson Glow

由於工作繁忙，主鏡運抵香港已近兩年，鏡筒組件也躺了一年多。直到昨晚終於把鏡運到城門河畔正式開光。幾點小分享如下，

- 這鏡焦距為2400mm f/3，配上Starlight Instruments Feather Touch調焦座及內置的TeleVue Paracorr II（SIPS），合成焦距 2760 mm。

- 搭配 100 度像場的 TeleVue Ethos 21 目鏡觀測時，放大率約 130 倍，實際視場為相當理想的 0.75 度，出射瞳孔為 6 mm，正好是中年觀星者視覺的上限。

- 尋星鏡使用 Askar 30 mm 導星鏡配 Meade 25 mm 標靶目鏡，機械結構十分穏固，對準目標既方便又可靠，能確保天體落在 Ethos 21 的視場之內。

- 觀測獵戶座大星雲時，碧綠色雲氣格外鮮明，細心觀察也可略暗的緋紅，照片為手持手機拍攝，這是小口徑望遠鏡難以企及的色彩層次，甚至大多數愛好者從沒見過星雲的顏色。

- 木星與四顆伽里略衛星排成一線，木星表面兩條雲帶色彩飽和，只可惜光軸因為小技術問題尚未完全精調，因此其他行星的細節仍受限，只算中口徑望遠鏡水平。

- 鏡筒結構扎實，光軸調校相當便利。搬運與裝拆雖需些許功夫，但目前仍可收納於 Tesla Model Y 後座與尾廂內，司機仍能多載一位乘客，會再進一步優化設計。

- 台架採用 OnStep 控制系統，仍需時間熟習其操作與自動導向功能。

未來一段日子會持續優化這鏡，提升使用效率。並會在觀星活動中服務。

方社長

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