M101 in LRGB

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oopfan
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M101 in LRGB

Post by oopfan » Thu Mar 28, 2019 1:34 am

I have mixed feelings about the quality of this image since I always strive to improve myself. What it's come down to is this: I've reached a plateau. I know what to do to make marginal improvements but the cost in time is high. So I present to you my last deep-sky image before retiring this camera from deep-sky duties: M101, a grand-design spiral galaxy.

My chief complaint is the noise level. In order to ensure correct star color rendering affected by saturation I reduced my normal exposure by half. As I've said many times in the past, this lowers your signal-to-noise ratio which you must make up with more stacking. Also, this time I did not go crazy capturing 50+ dark frames per half-degree Fahrenheit like I did with my landmark Bubble Nebula image seen here: viewtopic.php?f=16&t=1090

If I may, I want to address my critics who might say: Brian you talk a big game but you can't deliver. My reply to you is that this is a $250 uncooled camera that has served me well as a learning platform. Due to its inherent limitations I've learned what levers to pull to make positive things happen. In my opinion it is valuable. A lot of my knowledge comes from the friendships I've developed here in this forum and my membership to the American Association of Variable Star Observers (AAVSO) -- highly recommend. I await the delivery of my new camera with excitement.

Captured over two nights: 2019-03-13 and 2019-03-27

William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Optolong LRGB Filters
Unitron Model 142 GEM
The Flatinator
Passive tracking with PEC
No active guiding

Gain 200 (1.74 e-/ADU, FWD: 7100e-, Read Noise: 1.55e-)
Offset: 25 ADU
Exposure: Multiple
Camera rotation: 1.8 deg E of N

Lum: 47x 25s
Red: 82x 30s
Green: 90x 30s
Blue: 76x 36s

Flats: 50x per channel
Darks: 20x per channel
Bias: 50x all channels

Total integration time: 151 minutes
Total time at telescope: 300 minutes

SharpCap 3.1.5219
APP 1.072
StarTools

EDIT: I updated the image here: viewtopic.php?f=16&t=1533&p=8053#p8053
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turfpit
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Re: M101 in LRGB

Post by turfpit » Thu Mar 28, 2019 8:04 am

Nice image Brian. I like the detail in the object and the fact that you have retained colours in the stars. How old is the Unitron mount?

Dave

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oopfan
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Re: M101 in LRGB

Post by oopfan » Thu Mar 28, 2019 12:45 pm

Thanks, Dave.

Black Wikkkett has got an M101 here viewtopic.php?f=16&t=1412#p7373
that shows more detail. Three factors at play: twice the aperture as mine, active guiding, cooled camera less noise.

My mount is 50 years old. I added a stepper motor to R.A. with periodic error correction on a Raspberry Pi. Nothing on DEC.

Brian
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AndyBooth
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Re: M101 in LRGB

Post by AndyBooth » Thu Mar 28, 2019 3:55 pm

Its still a lovely image mate.

Its going to be clear here tonight, so i am out with the QHY10, see what I get.

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oopfan
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Re: M101 in LRGB

Post by oopfan » Thu Mar 28, 2019 5:24 pm

Thanks, Andy. Good luck tonight. Hopefully my camera will arrive soon. I'd like to get another chance at M101.

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Re: M101 in LRGB

Post by turfpit » Thu Mar 28, 2019 5:42 pm

Like the rig Brian - some engineering and programming gone into that.

Dave

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Re: M101 in LRGB

Post by BlackWikkett » Thu Mar 28, 2019 7:02 pm

Nice image

AndyBooth
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Re: M101 in LRGB

Post by AndyBooth » Thu Mar 28, 2019 8:30 pm

Oh no , high cirrus :evil:

What camera are you getting Brian (sorry if youve said previous ).

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oopfan
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Re: M101 in LRGB

Post by oopfan » Thu Mar 28, 2019 10:39 pm

Thanks, Mr Wikkett, but not as nice as yours.

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Re: M101 in LRGB

Post by oopfan » Thu Mar 28, 2019 10:43 pm

Andy, I'm taking the plunge into CCD. I did my own analysis of high read noise inherent in CCDs and concluded that its effects are largely mitigated by having the 16-bit A/D. We'll see!

Brian

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