www.astrocafe.hk

Dear all,

Auto-guide does make a big difference in S/N and clarity of each sub-frame.

This M51 was taken in earch March 2013 in 4 days (same timing as NGC 3628) when the transparency was high on 8th & 9th. Thus a single 10 min autoguided sub-frame produce lots of details in L filter.

Total exposure was 6.3 hrs (mix of some 10 mins, 5 mins sub-frames). Thus longer makes a difference.

This M51 is also my 1st record-breaking of prolonged exposure exceeding 6 hrs. Only made possible by remote operation & fixed observatory site, since most exposures were taken during weekdays, not very friendly to daytime worker.

http://www.raymondtse-lawyer.com/astro/ ... IK314L.htm

Raymond Tse

好奇你如何把5及10分鐘的曝光混在一起處理?

There are one 180s, one120s & one 84s. Just combine all 47 sub frames by mean or median.

Raymond TSE 寫:There are one 180s, one120s & one 84s. Just combine all 47 sub frames by mean or median.

那恐怕會弄巧反拙

愿闻其详。

看來Raymond不是把不同曝光組別個別疊加後再用Layer合成? 按理M51也用不到這樣做。

若把不同曝光的混在一起，就會弄巧反拙。

因為除噪就是從統計學上把非訊息除去，希望得出那一個特定曝光下的高訊噪比訊息，但若果訊息本身都是變數，那如何除? 那些跟主流有異的曝光，加進去就會影響整個Distribution，繼而影響除噪效果。