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eshy76

Markarian's Chain and M87 - LRGB - 25-29 March

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Posted (edited)

Hi everyone,

This is Markarian's Chain shot from my back garden over three nights in late March. Probably the deepest single image I've taken in terms of integration time...which leaves me feeling my processing is not quite doing the data justice...maybe I'll come back to it.

In any case, this is an incredible part of space; looking away from our galaxy reveals countless others!

The crazy number of Lum subs took a whole day for APP to chug through and so I've resolved to lower the gain from unity going forwards to get more manageable sub lengths than 15 seconds!

L: 1050 (!) x 15s R: 92 x 60s G: 165 x 30s B 165 x 30s....total integration time 8.2 hours.

Captured using APT, stacked in APP and processed in Pixinsight.

Thanks for looking!

Edit: Link to higher res version


1120066042_MarkariansChain2019-03-25.thumb.jpg.f4d0736bd743eaf23b6281f671bbebc5.jpg

Edited by eshy76
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Very nice image. A lot of short subs to crunch. 

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7 hours ago, tooth_dr said:

Very nice image. A lot of short subs to crunch. 

Thank you! Yes indeed...so while I got, erm, stacking benefits, the practical side was an issue in terms of the time it took to stack on a good PC. I also didn't dare drizzle the integration - that might have taken 2 days!

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35 minutes ago, Demonperformer said:

There are a lorra lorra galaxies in that image. Nice one.

Thanks! Yes - an incredible part of space. There is a tiny barred spiral in the bottom middle of the image which is just beautiful and perfectly formed...I'll focus on that one one day when I have some more focal length!

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I like this it is a very nice image and I wonder how many more are there we can't see.

A question what advantage is there in doing so many short subs over fewer longer ones?

Alan

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1 minute ago, alan potts said:

I like this it is a very nice image and I wonder how many more are there we can't see.

A question what advantage is there in doing so many short subs over fewer longer ones?

Alan

Thank you! That is the golden question which I intend to find the answer to - with my level of light pollution, 15 secs at unity gain on my camera is more than enough for my Lum subs to drown out the read noise...so I've always used that sub length...

...which was fine for 200-300 subs, but this project really brought home the impracticality of stacking 1000+ subs. I just was thinking in terms of total Lum integration time (250 mins) and set the number of subs that way.

As far as I am aware, SNR benefits of stacking enter the realm of diminishing returns from about 200 subs onwards...so going forwards I'm going to lower the gain from unity (139 on the ASI1600) to 76 or 0 to try and get sub length up to between 30s and 60s and hopefully more like 200-400 subs to stack.

I can then answer your question fully. The 15sec approach benefits in terms of guiding being less critical, and things like clouds or planes or satellites not meaning minutes of data being binned. The Lum integration WAS beautifully smooth at least!

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Posted (edited)

There is a video on here somewhere produced by rwg who goes into details of optimal sub length. I'l track it down for you when back on desktop.

As regards stacking, if you use sharpcap, you could stack them as you go along.

Edited by Demonperformer
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I remember seeing something which in truth was Concorde for me, miles over my head, about short subs and CMOS sensors. I intend to get a couple of cameras this year, maybe a 071 and a 183 for my range of scopes. I am sure you would love to visit here where on a decently transparent you can see M33, but it does get almost overhead. Still what ever you have to do, it is still a lovely capture or should I say lots of captures.

Alan

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51 minutes ago, Demonperformer said:

There is a video on here somewhere produced by rwg who goes into details of optimal sub length. I'l track it down for you when back on desktop.

As regards stacking, if you use sharpcap, you could stack them as you go along.

Thank you - that sounds interesting - I like the theory side of things as a guideline to what I do! And I did not know that about Sharpcap...I've got the pro version for the polar alignment routine, but have been using APT for capture. 

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20 minutes ago, alan potts said:

I remember seeing something which in truth was Concorde for me, miles over my head, about short subs and CMOS sensors. I intend to get a couple of cameras this year, maybe a 071 and a 183 for my range of scopes. I am sure you would love to visit here where on a decently transparent you can see M33, but it does get almost overhead. Still what ever you have to do, it is still a lovely capture or should I say lots of captures.

Alan

I hear you! The basic theory is that each sub should be long enough to drown out the read noise and with the really low read noise of CMOS cameras, that level is reached quickly with light pollution. Of course you can shoot longer than that for practicality, but if subs are too long, stars and highlights could get saturated. That is it in words - there are mathematical formula that try to calculate the optimal sub lengths!

Those cameras have really good reputations - I was looking at a 071, but ended up getting a 294, which I'm still learning. I think the 071 has an APS-C sensor?

Thank you for the kind words!

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Great picture.  Very difficult to tease out the colour on this subject, there is not a lot there but you've done it great.

For sure, my next camera will be a CMOS.

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31 minutes ago, Demonperformer said:

Here is a link to the video. This is good if you wish to explore the theory a bit further.

Thank you very much! Something to devour this weekend!

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29 minutes ago, kirkster501 said:

Great picture.  Very difficult to tease out the colour on this subject, there is not a lot there but you've done it great.

For sure, my next camera will be a CMOS.

Thank you!

I really wanted to bring out the blues more but the data was not cooperating...in any case it's a nice data set to come back and add to. The background is a mottled black too - I actually think that is the beginnings of IFN (integrated flux nebula), but the integration time was too low and the light pollution too high to get close to bringing that out as pretty dust.

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By the way, NGC 4440 was the pretty barred spiral galaxy I was referring to earlier....you will be mine one day!

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Great image and a great thread! Right now I’m sticking with CMOS cameras for small galaxy targets. Having cut my teeth on a KAF 8300 camera, the shorter subs were really counter intuitive but I saw Robin Glover’s lecture at the PAS, and I’m just doing what Sharpcap recommends, running at 20-30 s for Lum and three times that for RGB, and the results I have obtained to date are very encouraging. A 1000+ subs to integrate is a bit daunting, but APP does get there in the end.

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Thank you tomato! I went straight to CMOS, so short subs is all I know...looks like Sharpcap does a lot more than just polar alignment...I need to take a closer look.

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Yes, up until recently I only used SharpCap for Polar Aligning (which it does really well), but the sensor calibration and smart histogram features really seem to work with the CMOS cameras.

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9 hours ago, David_L said:

Excellent effort!

David

Thank you!

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On 26/04/2019 at 11:12, Demonperformer said:

Here is a link to the video. This is good if you wish to explore the theory a bit further.

I watched the vid and read those posts yesterday - superb! The new stuff versus what I had read before was actually getting a number for light pollution and incorporating that into the equations.

It was an impressive presentation and makes me want to dig deeper into Sharpcap, if its creator is so knowledgeable.

Thanks again for sharing!

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For me, the biggest help has been the live stacking option. It does all the DSS  stuff while the capturing is going on. Even if you use multi-sessions, you stil only have one stacked image per session to do in DSS. Really opens up the "lots of short subs" approach that seems to suit these CMOS cameras so much.

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