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網誌日期：2009-08-06 14:21
這幾天忙著好些事，讓電腦不停做背景處理，調這個調那個，最後得出以下一段木星自轉面貎，處理過程中發現有個別幀其實還未最優化，但在這種很一般的視寧度下能拍到這個樣子，筆者認為可以初步停手了，因為確實夠累了…..
一些拍攝資料：
APM 203 APO折射鏡、派拉蒙赤道儀、映美精DBK21相機、Televue 5x Powermate
2009年8月1日早上02:39-03:08 (歷時30分鐘)
視寧度3/5，透明度4/5
共拍攝12段2分鐘視頻，每段拍攝間距~30秒，合成12幀的GIF動畫
影像分析：
經過細緻比較，部份細節是會隨木星自轉移動的，證實為木星表面特徵而非訊噪，量度後發現，在高對比度區域，解像度約在0.2”水平，以7000mm有效焦距下，相機晶片每像素解像度約為0.16”，以203口徑望遠鏡及視寧度3/5水平來說，這段影像應屬合格水平了。
DBK彩色相機比DMK黑白相機在解像度、感光度、訊噪上都有差距，但優勢是容易操控，故一些國際級的作品都是以DMK21相機配合三原色濾鐿拍攝，而DBK則用於初中階拍攝，或個別大師用於拍攝爭分奪秒的景像，例如木衛互掩等情景。
另外從12幀組成的木星30分鐘自動圖中可看到，每段2分鐘視頻，拍攝間距也僅30秒上下，但已看出木星面細節明顯移動，對203口徑望遠鏡的有限集光力來說，7000mm有效焦距F35光圈，曝光只能短至1/30，2分鐘最多能產生3600幀，故此這些指標也限制了有關影像的質量。
筆者已把有關設備移回白鷺湖天文台，會靜待8月衝日前後理想視寧下再戰，期望有更好的作品分享，有興趣參與同好，可於筆者發起的Facebook群組星空之城登記。
Galaxy Kid 2009-08-06 18:24
hello Oldfield, thanks for the input. To be honest I doubt if it works under 1/20 or so, especially for this aperture.
for 1/30s exposure, I can get 3600 frames from 2min, but 1/27s or below, it will go down to 15fps. The chance of getting good frames due to longer exposure is lower, and the number of good exposure from the reduced total frames (only 1800 left) is also reduced. So the overall result may be even worse.
If I don't want those noise, I can simply don't use wavelet 1 and only work on 2 and 3. But I want to fine details, so I endure the noise a little bit......
anyway, will keep on trying, I am still learning on this.
oldfield 2009-08-06 18:16
The prime purpose for stacking is to reduce noise, so it does not make much sense to bump up the noise (gain) only to get more frames (faster shutter). It defeats the purpose entirely.
Of course, if the seeing is worse, it makes some sense to use faster shutter to freeze the seeing, but then I would say if the seeing is that poor, we better wait for better chance.