草山星空: 冬季銀河與冬季大三角，繼續累積女巫頭的曝光／Pentax MS-3 漂移修正極軸備忘/購入新的EM-2S控制把手

12/14 雙子座流星雨

今年的天氣晴朗且沒有月娘當電燈泡，流星雨相當精彩，陽金公路、巴拉卡公路上擠滿了車流與人潮，更不用說停車場內了，跟慶典一樣熱鬧。

先貼一張在這篇，其他等有空再處理了。

12/8~9

今晚鞍部無風，雖然氣溫最低來到12度左右並不會感到寒冷，不過濕度高，所以入夜後就開啟了望遠鏡的除霧線。

今晚使用 Pentax MS-3 進行單軸自動導星，因為前幾天我的高橋EM-2S 的馬達驅動板損壞，在修復前我便先玩這台（由於有好一陣子沒用它了，早上我先校正了一下極軸鏡的歲差）。

花了些時間重溫MGENII飄移法修正極軸的步驟，最後得到追蹤的準度超過我的預期。

MGENII的對極軸法其實就是我們熟悉的飄移法，只不過以CCD來輔助並計算有效率且精確多了。修正到誤差在2'以內，就至少足以進行單軸導星曝光三分鐘不托線。

今晚總共累積了3.5小時的IC2118 女巫頭，與之前曝的兩小時一起疊合，先簡單處理一下。目標預計要至少曝光十小時。

除了累積IC2118的曝光時間，今晚也用 Pentax 10-17mm拍攝星景。個人覺得 Pentax 這顆光學素質比Samyang的 8mm 好很多，Pentax F4就是可用光圈，Samyang要縮光圈到約F6.5像差才會有較多的改善。

On Friday night, the weather at Anbu was clear and windless, so even when the temperature was as low as 12 C, it did not feel very cold. This time I brought the Pentax MS-3 (single-axis guideing mod.) equatorial mount with me, and I took some time to review the drift method of correcting the polar axis with MGENII. I achieved very good accuracy, with an average roundness of 0.9 for 3-minute exposures (540mm focal length ). Then I continued to accumulate exposures of the Witch Head Nebula (IC2118) . I exposed for about 4 hours that night.The preliminary goal is to accumulate a total exposure time of 10 hours，now i have 5.5 hr total. In addition to exposing the nebula,I used the Pentax K3II with a 10-17mm lens to imaging the starry sky. The optical quality of the Pentax 10-17 is much better than the Samyang 8mm I used before. F4 is a usable aperture, while the Samyang's aberration is only reduced when the aperture is reduced to about F6.5. This night I used ASTROTRACER to expose 80 seconds per frame. Most of the images were exposed 8 frames and then aligned and stacked with Registar.