M64 in a 12" Dob

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robrj
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Joined: Fri Feb 17, 2017 1:03 am

M64 in a 12" Dob

Post by robrj » Sat May 05, 2018 3:47 pm

I took this two nights ago. M64 in my 12" Skywatcher goto dob. ASI294MC Pro.

155x8s, gain 400:

Image

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oopfan
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Re: M64 in a 12" Dob

Post by oopfan » Sun May 06, 2018 12:05 am

Very nice!

Minor point: You're North-South is correct but East-West should be flipped.

Also, the DSS image shown in Deep-Sky Planner shows arms extending farther from the galactic core. Since these faint details are down close to your read noise try doubling the exposure and halving the number of subframes -- you will get better signal-to-noise as opposed to simply stacking more subs at the current exposure.

Brian

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oopfan
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Re: M64 in a 12" Dob

Post by oopfan » Sun May 06, 2018 2:03 pm

I've attached the performance graph from ZWO's website. I noticed that your gain setting of 400 appears to be the highest available on your camera. Is that right? If true then your well depth is barely 1000 electrons which means poor dynamic range and that stars are saturating. A better choice would be gain of 120. That gives you great dynamic range and a well depth of 10,000 electrons. Astrophotography is about capturing the most number of photons (i.e. electrons). Increasing gain does not increase electrons but it does set a cap on the number of electrons that a pixel can hold. In my experience the lower the gain the better especially if you are trying to capture a faint DSO with 10th magnitude stars in the FOV. When I image I let my guiding determine the exposure. Some nights I can get 100-second exposures, and other nights 10-second exposures. Once I determine the exposure then I adjust the gain to prevent the brightest object from saturating whether that be a star that I can't crop out or the core of a galaxy.
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robrj
Posts: 53
Joined: Fri Feb 17, 2017 1:03 am

Re: M64 in a 12" Dob

Post by robrj » Mon May 07, 2018 2:04 pm

Thanks for the tips. I don't recall off hand but I think the gain goes up quite a bit more. But I'm doing video astronomy, which is why I crank the gain. The purpose is to see it near live. I just capture what I've seen and then use Startools to clean it up as best I can. But the final image isn't my end goal.

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oopfan
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Re: M64 in a 12" Dob

Post by oopfan » Mon May 07, 2018 5:37 pm

Thanks for the added info, and glad to meet a fellow StarTools user!

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oopfan
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Re: M64 in a 12" Dob

Post by oopfan » Mon May 07, 2018 6:35 pm

Just a thought...

I really like the auto-stretch feature in SharpCap. Try decreasing gain and then turn on auto-stretch! Decreasing the gain will give you more dynamic range. Auto-stretch will give you something similar to StarTools "AutoDev".

Brian

robrj
Posts: 53
Joined: Fri Feb 17, 2017 1:03 am

Re: M64 in a 12" Dob

Post by robrj » Mon May 07, 2018 9:17 pm

Okay. I'll give it a shot next time out.

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