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A couple of firsts for me: NGC6888

Adam J

By Adam J
in Imaging - Deep Sky

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Adam J

Adam J

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With the short nights and poor UK weather over August myself and @PadrePeace (Chris) decided to make the most of the imaging time available by working on our first pre-planned collaboration and also my first narrowband image using my new mono camera.

We both image using Newtonians and so that presented some additional challenges with aligning the diffraction spikes between our two imaging setups.  We solved this issue by rotating our scopes in their tube rings until our diffraction spikes intercepted an agreed star close to Altair.

1985193003_CresentRotation.jpg.a1a245a5d4d110db09995baa4e50b38e.jpg

We decided that Chris would focus on gathering the OIII data due to him having the superior OIII filter in the form of a 5nm Astrodon Vs my 8.5nm Baader filter and that I would focus on gathering Ha using my 7nm Baader filter. Having said this we both upgraded out filters at the end of August and so a few of the final frames were captured using a 5nm Astrodon Ha and a 3nm Astrodon OIII filter.

Chris Images with a 150PDS and a ATIK460EX mono camera and I use a 130PDS with a ASI1600mm pro. This gives me a much larger field of view at a near identical image scale of 1.24 arc-seconds per pixel.

We originally started with the intention of getting a single panel each for a reasonably close in look at the Crescent Nebula aiming for 6 hours per channel, however as we got several good nights in early August with Chris having much better luck with the clouds than me despite only living 20 minutes drive away ?, so we decided to expand the OIII to an additional panel to cover the Soap Bubble and better use the field of view available from of my setup. 

This is:

120 x 240s Ha (8 hours)

96 x 600s OIII (16 hours over two panels)

Not sure if it was just pure luck but the star size was very well matched between the channels using these exposure lengths.

My Processing in Astro Pixel Processor (APP) and Photoshop CS2.

2010533069_Cresent_HOO_FINAL_09092018-3-nr1080p-2.jpg.edcb228903a129f00f1cd8f7703d2ce7.jpg

I found this a difficult image to process with the balance between the Soap Bubble and the Crescent + Background nebula hard to achieve.

Chris did a great job on the OIII for the Bubble!

Thanks for looking.

Adam.

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jjosefsen

jjosefsen

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Wow this is really great, well done to both of you! I love the idea of collaborating on a project, it must have been really satisfying to get a result this good from your first(?) joint project.


What gain settings did you decide to use for the asi1600? 4 minute subs are quite short, but obviously effective.

 

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Adam J

Adam J

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On 04/10/2018 at 00:02, jjosefsen said:

Wow this is really great, well done to both of you! I love the idea of collaborating on a project, it must have been really satisfying to get a result this good from your first(?) joint project.


What gain settings did you decide to use for the asi1600? 4 minute subs are quite short, but obviously effective.

 

Thanks, I used unity gain, I would probably say that 4 min subs are quite long for the ASI1600 lots of people use 60s and gain 200. But I dont want to deal with the number of subs that results in.

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Demonperformer

Demonperformer

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On 04/10/2018 at 00:02, jjosefsen said:

4 minute subs are quite short, but obviously effective.

From FLO's write up of these cameras:

" Imaging with CMOS will probably require a different approach, tests suggest more frames / shorter exposures work better than less frames / longer exposures. This takes advantage of the CMOS sensor's very low read noise and stacking more frames suits the type of data CMOS sensors produce (12 or 14-bit, rather than the 16-bit we are used to)."

But, as Adam says, the number of subs goes up dramatically and, at 32MB at pop, so does the disk space they take up ... and the amount of processing time required ... and ...

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Demonperformer

Demonperformer

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1 hour ago, blinky said:

but how can i tell?

I would need to go looking to find the original article, but the formula I use is:

t=(T/n) = (1/(1.052-1))x(σr2/(Q x rp,sky))

where:

t   = sub duration
T   = total imaging time
n   = number of subs
σr  =  read noise
Q   = quantum efficiency at the filter wavelength
rp,sky  = skyglow (photons/px/s)

 

 

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jjosefsen

jjosefsen

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9 hours ago, Adam J said:

Thanks, I used unity gain, I would probably say that 4 min subs are quite long for the ASI1600 lots of people use 60s and gain 200. But I dont want to deal with the number of subs that results in.

Yeah I see your point, I am just so used to seeing these amazing pictures where people shoot 10, 20 and 30 minute NB subs. :)

I hope to start my first NB project early next week, where it looks like I will finally be getting some clear skies.

Again.. Great image, that OIII shell is truly beautiful..!

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Adam J

Adam J

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13 minutes ago, jjosefsen said:

Yeah I see your point, I am just so used to seeing these amazing pictures where people shoot 10, 20 and 30 minute NB subs. :)

I hope to start my first NB project early next week, where it looks like I will finally be getting some clear skies.

Again.. Great image, that OIII shell is truly beautiful..!

https://www.cloudynights.com/topic/599475-sony-imx183-mono-test-thread-asi-qhy-etc/

read this thread, its for the cooled ASI183mm pro camera that has the same chip as your 183m V2 so much of the discussion is still relevant in terms of optimal settings. 

From this I would not go too high on the gain with the IMX183m and focus more on unity. Without cooling I would also be looking at shorter subs so 2 - 5min dependent on the ambient temperature. 

Adam 

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jjosefsen

jjosefsen

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56 minutes ago, Adam J said:

https://www.cloudynights.com/topic/599475-sony-imx183-mono-test-thread-asi-qhy-etc/

read this thread, its for the cooled ASI183mm pro camera that has the same chip as your 183m V2 so much of the discussion is still relevant in terms of optimal settings. 

From this I would not go too high on the gain with the IMX183m and focus more on unity. Without cooling I would also be looking at shorter subs so 2 - 5min dependent on the ambient temperature. 

Adam 

I  am reading it in fact. :) Jon Rista is a hell of a repository of knowledge..!

I have run sensor analysis from SharpCap, so I know the Unity gain is around 400, I guess some tests under actual skies is the next step.

Doing shorter subs will help me massively when shooting darks, without setpoint colling i can't really make a darks library. So the prospect of doing 15-20 darks at 5-10 mins exposure each session had me shuddering tbh..

 

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Adam J

Adam J

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2 hours ago, jjosefsen said:

I  am reading it in fact. :) Jon Rista is a hell of a repository of knowledge..!

I have run sensor analysis from SharpCap, so I know the Unity gain is around 400, I guess some tests under actual skies is the next step.

Doing shorter subs will help me massively when shooting darks, without setpoint colling i can't really make a darks library. So the prospect of doing 15-20 darks at 5-10 mins exposure each session had me shuddering tbh..

 

If it was me I would leave the camera outside / in a shed for a few nights when not imaging taking darks at 2.5 mins and 5 mins and as the temperature changes from night to night and hour to hour you will get dark frames of different temperatures (repeat as the nights get colder). It means you have to store a tone of frames but as you get more the chances of you having collected darks that are of the same temperature as your lights increases, then you just sort the frames into temperature ranged folders and match them up.

Its still a dark library its just a very big one and much more intensive to create, but once you have darks at a given temperature you should be sorted. 

Adam

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