Crab nebula ASI120mm

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NDB
Posts: 123
Joined: Tue Dec 10, 2013 12:17 pm

Crab nebula ASI120mm

Post by NDB » Tue Jan 21, 2014 3:44 am

m1_newt254-f3,9_asi120mm-bin2x2-170x20s-gain60_ndb.jpg
This "planetary" camera is brilliant ! Simple and fast post-processing, automatic darks, no need for flats (small sensor and protection window), nor autoguiding... I added a Celestron 0.63x reducer corrector to the f/D=4.7 newton (simply pushed it into the 2" eyepiece holder...). This was not necessary because the camera is sensitive enough to capture M1. No filter despite a light-polluted, suburban sky. The automatic dark subtraction by FireCapture even wiped out the offset.
I choosed a 2x2 binning to have light enough, AND to conceal the erratic behaviour of my EQ6.
Nicolas.
EDIT: reprocessed with Photoshop.
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m1_newt254-f3,9_asi120mm-bin2x2-170x20s-gain60-reprocessed_ndb.jpg

skywatcher
Posts: 101
Joined: Sat Mar 23, 2013 7:45 pm

Re: Crab nebula ASI120mm

Post by skywatcher » Tue Jan 21, 2014 2:42 pm

belle image ,
c'est interessant cet essai de mettre un réducteur de focale sur le newton, en tout cas c'est pas commun,
comment traites tu les dark et les offset ?
je suis pas trop la méthode sous fire capture !
Daniel

NDB
Posts: 123
Joined: Tue Dec 10, 2013 12:17 pm

Re: Crab nebula ASI120mm

Post by NDB » Tue Jan 21, 2014 3:09 pm

Thanks Skywatcher, but please, write in english or chinese. ;)

I neglicted the offset subtraction. Since the offset of the ASI120mm is quite low, it doesn't really matter (for this kind of images).

One dark frame is acquired at the beginning of the capture with FireCapture (which asks to place the cover onto the scope, then to remove it after the dark is acquired). Then FireCapture automatically subtracts the dark from all of the images during the capture. You have just to take care of the temperature gradient during the session. It decreased from 15°C downto 12°, and the signal of the dark was too high in the last frames (dark spots in the raw images). The stacking process dimmed this drawback. Perhaps, in the future, ZWO will add a small regulated TEC...

I took 170 TIFF images (16 bits), then stacked them with DeepSkyStacker.

I'd rather take and subtract a flat, too... But that's a first try.
Nicolas.

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Sam
Posts: 2799
Joined: Thu Feb 21, 2013 2:51 am

Re: Crab nebula ASI120mm

Post by Sam » Wed Jan 22, 2014 5:36 am

that's great shot!
winter is the best season for DSO :)
ZWO Founder
Location:lon=120.6 lat=31.3
SuZhou China

NDB
Posts: 123
Joined: Tue Dec 10, 2013 12:17 pm

Re: Crab nebula ASI120mm

Post by NDB » Wed Jan 22, 2014 7:14 am

Thank you Sam!
It could be better (flat frame, better focusing, focal reducer placed perpendicularly to optical axis, H-alpha filter and so on), but it's already thrilling!
Great camera.
Nicolas.

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