Sunday, December 17, 2006

20061217 M41

Temperature dropping these days, we finally enter winter. Cloud usually go away when it's becoming cold, but we must change the first few days (maybe just first one or two days) before the air stablized and get foggy by air pollutants.

Again, I don't have a chance to go out, got to stay at home.

Sirius is just outside at around 4:30am... of course, the natural target would be M41.... I used the 25mm lens this time, not because I want it, but it happens that I picked it up first. So, I feel 25mm is wide enough and not too low power.

Nothing, couldn't find anything. So I digged out my 10x50, couldn't locate too... star charts verified that I probably looked at the right point.

Then, I set my 75mm lens... scan around, I finally found it! It's pretty small, not much bright star (take a highly light and air polluted city in mind), and thus it's hidden with smaller lens.

Replace it with a 150mm lens, it's certainly M41... adjust exposure and shutter length (reduce gain and increase shutter I mean), here we go... but the polar alignment is found to be way off... carefully adjust it slowly while keeping it partially in the field, slew back... again and again... finally not too far away.

Still not accurate for sure, using this approach. Anyway, I stopped somewhere when I feel my exposure will not be too long, compromise.

This is what I settled for (500 gain, 9.7s... captured 50 frames like this and then adjust to 605 gain to capture some more).

Focus is a bit soft:

15 minutes total exposure.

No comments: