www.astrocafe.hk

Dear all,

Even though last night was foggy with high up full Moon, still tried to quick test the Ha focusing with reference to the OAG and how the bright full Moon (age 16) on 20-10-2013 am would affect the S/N of narrowband 4.5nm Ha image.

Capture details at :-
http://www.raymondtse-lawyer.com/astro/ ... TIK490.htm

I expect another 10-20 hrs exposure before I could reveal the fine details of the head features.

Raymond Tse

我在西藏拍5nm Ha也是用離軸導星器，及在濾鏡後導星的(Guide behind filter)，曝光是3秒，至今拍了兩年百多個天區，從沒有遇到找不到導星問題。

馬頭這個目標很值得長時間累積曝光，在香港也很有發揮空間，希望早日看到成品

我的Ha通道未處理，下面是L通道的，加上沒有你的組合解像度高，星點當然會肥大一些：

viewtopic.php?f=17&t=3604#p23813

Dear Savio,

Your Orion Wide Field is magnificent and speechless. 6.5 mag sky has an edge in wide field.

Due to the high light and dust pollution in HK, my narrow FOV 45x30 ar min would only be suitable for revealing very fine details by use of high resolution per pixel.

I hope to get better S/N by increasing exposure to 20 min per frame to reveal the fine head features and the surrounding Ha clouds. Waiting for a few more nights of clear skies.

Raymond

Raymond TSE 寫:Dear Savio,

Your Orion Wide Field is magnificent and speechless. 6.5 mag sky has an edge in wide field.

Due to the high light and dust pollution in HK, my narrow FOV 45x30 ar min would only be suitable for revealing very fine details by use of high resolution per pixel.

I hope to get better S/N by increasing exposure to 20 min per frame to reveal the fine head features and the surrounding Ha clouds. Waiting for a few more nights of clear skies.

Raymond

6.5th mag sky 太差了

以前Sky & Telescope提過，一些美洲大陸的高海拔星空派對，個別人士目視可達8等，用Televue 4"折射可以目視冥王星。所以西藏對多數人來說肯定是 7th mag Sky甚至更暗的天空，要知道在那海拔，因為大氣減光減少，所以實際上Sky Quality Meter數據會比海平面亮了零點幾等，我很小心避開銀河或較多亮星的天區，但也不可能量到暗於22等的讀數，開發人說實際上到21.8等左右已是SQM的可靠最暗讀數，而我在高海拔還要減些許。例如在那次在阿里5000海拔，銀河在仰角十多度，上面的暗黑結構已很明顯，天空根本是灰色不是黑色的。

e.g., 我在仰角不足10度，單張曝光3分鐘已可把14等彗星拿下。

有個說法是吸吸純氧有助瞳孔放大，或許12月底我們的西藏星空派對，到納木錯時會每人帶一個專用氧氣筒，可以用數天的....

我相信你的觀測站已上軌道，期望不久未來看到這張馬頭成品。

社長 寫:

Raymond TSE 寫:Dear Savio,

Your Orion Wide Field is magnificent and speechless. 6.5 mag sky has an edge in wide field.

Due to the high light and dust pollution in HK, my narrow FOV 45x30 ar min would only be suitable for revealing very fine details by use of high resolution per pixel.

I hope to get better S/N by increasing exposure to 20 min per frame to reveal the fine head features and the surrounding Ha clouds. Waiting for a few more nights of clear skies.

Raymond

6.5th mag sky 太差了

以前Sky & Telescope提過，一些美洲大陸的高海拔星空派對，個別人士目視可達8等，用Televue 4"折射可以目視冥王星。所以西藏對多數人來說肯定是 7th mag Sky甚至更暗的天空，要知道在那海拔，因為大氣減光減少，所以實際上Sky Quality Meter數據會比海平面亮了零點幾等，我很小心避開銀河或較多亮星的天區，但也不可能量到暗於22等的讀數，開發人說實際上到21.8等左右已是SQM的可靠最暗讀數，而我在高海拔還要減些許。例如在那次在阿里5000海拔，銀河在仰角十多度，上面的暗黑結構已很明顯，天空根本是灰色不是黑色的。

e.g., 我在仰角不足10度，單張曝光3分鐘已可把14等彗星拿下。

有個說法是吸吸純氧有助瞳孔放大，或許12月底我們的西藏星空派對，到納木錯時會每人帶一個專用氧氣筒，可以用數天的....

我相信你的觀測站已上軌道，期望不久未來看到這張馬頭成品。

>7.1 = darkest skies

http://www.ayton.id.au/gary/Science/Ast ... lution.htm

再計及4000+海拔避免了大氣減光約零點幾等星，所以Sky & Telescope提及的8.0 mag sky不是神話。

Congratulation if Tibert has around mag 8 sky.

Delighted to see Victoria Province in Australia has 7.1, slightly better than NSW.
Good choice to consider this location for South Hemisphere remote operation.
Would try to measure it with SQM in the near future.

我不會說西藏是8th Mag的天空，因為那篇Sky & Telescope的文章是十多廿年前看的，印象中也提及是某人的目視等，或許他的視力特別好。

但西藏肯定不只6.5th Mag，一定是7.0th Mag以上的。

注意由設計所限，SQM能量出最暗而可靠的天空亮度是21.8。再暗的讀數，例如那個22等多的納米比亞讀數，是受天氣影響而不可靠的，我也很相信在無月密雲的晚上，西藏隨時量出22、23、24等的讀數。另外在西藏的高海拔的地方，因為大氣密度低了一半，星光也比海平面亮了好像0.3或0.4等，所以我在西藏西陲阿里海拔5000米的山上，方圓百公里內沒有一顆燈，白天空氣清澈可看見五六百公里外的雪山，可以肉眼目視農曆廿七的月亮月落(上方30多度是刺眼的太陽)，濕度隨時是單位數，在那條件下，量出來的SQM讀數也是21等多而已。為此我跟SQM的開發人討論過，他更多借一部SQM給我到西藏對比一下，結果是一樣的。

在阿里，黃道光對攝星很困擾，滿月月出時僅昇離地平線，已是刺眼的螢亮的銀白色，若哪天稍為暗淡，已說明當天的空氣質量不好

題外話，八十年代陳玉麟未入職教師前，和幾位觀天會人士，在黃竹坑工業區搞哈雷儀器社賣自製鏡及十小時自製望遠鏡保證完成班，那時劉佳能在那工廈天台經常通宵達旦拍長焦木星(隨時單張曝光15秒的)，也在觀天會會訊天樞說過黃竹坑天台的目視星等是6等。