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M45 Pleiades

Posted: Tue Sep 25, 2018 9:18 pm
by turfpit
_M45-30x60s-g250-bl350.jpg
_M45-30x60s-g250-bl350.jpg (188.6 KiB) Viewed 832 times
Altair Lightwave 66ED, Planostar 0.8x flattener/reducer, Celestron AVX mount, Altair 183M camera.
SharpCap + FITS Liberator + Siril + GIMP 2.10
Focus with Bahtinov mask, unguided.

30x60s, gain=250, black level=350
30 lights, 15 darks, 100 flats, 50 bias

As M45 was captured around 03:00 and was getting near the Meridian, I reduced the number of exposures but upped the gain and black level. I will retry the object with my more usual gain=100, black level=100 settings but increase the number of captures.

Dave

[ALTAIRH183M]
Output Format=FITS files (*.fits)
Capture Area=5440x3648
Binning=1x1
Pan=0
Tilt=0
Colour Space=MONO12
Fan=Slow
Temperature=6.8
Black Level=350
USB Speed=2
Auto Exp Target=120
Frame Rate Limit=Maximum
Analogue Gain=249
Exposure=60000
Timestamp Frames=Off
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1
TimeStamp=2018-09-24T01:50:58.6350529Z
SharpCapVersion=3.2.5762.0

Re: M45 Pleiades

Posted: Fri Sep 28, 2018 11:18 pm
by mAnKiNd
Nice one Dave!

Re: M45 Pleiades

Posted: Fri Sep 28, 2018 11:50 pm
by turfpit
Thanks Minos.

Re: M45 Pleiades

Posted: Sun Sep 30, 2018 10:58 pm
by oopfan
Good work, Dave.

Gain 100 has its pluses and minuses. The advantage is that the bright stars will saturate less. The disadvantage is quantization error. At the lowest gain setting my camera's gain is 3.62 e-/ADU. I think that is similar to yours. Unfortunately that means that you only see multiples of 4.83 photons for each ADU count (assuming 75% quantum efficiency). For a lot of objects this isn't a big deal but for the Merope Nebula you want to see the subtle variations in luminance across its width and breadth.

I would suggest keeping the gain the same but dramatically increase the number of dark frames. That will do the most to suppress the noise.

Brian

Re: M45 Pleiades

Posted: Mon Oct 01, 2018 12:08 am
by turfpit
Thanks Brian, I will try that. I am usually taking 50 darks for 60 or more lights.

Dave