NGC7331 - lacks detail

[strivedi]

Hi,

I have acquired 4x20min L and 10x5min each of R, G, B and processed NGC7331 using the flow by kayronjm at:

http://lightvortexastronomy.blogspot.com/2013/02/tutorial-pixinsight-workflow-for-hdr.html

I have spent many hours trying to extract nebulosity in the spiral arms but I am unable to get sufficient detail.

I want to get to the level of some of the great processing done at the NGC7331 October 2013 challenge at:

http://pixinsight.com/forum/index.php?topic=6221.0

Either I am doing something incomplete/incorrect or my data is not good.

Any insights into work flows for NGC7331  or what I might be doing wrong is greatly appreciated.

I captured using an AT8RC scope on a Paramount MX with a SBIG ST8300M camera with filterwheel & OAG.

I know I have dust on my camera sensor and could not take flats.

Here are the FIT files at the drop box link below:

The non linear files (luminence, RGB & LRGB files)

https://www.dropbox.com/s/ygxip458m3qtgw2/Luminence.fit
https://www.dropbox.com/s/wvztockdlfex50n/MasterRBG_DBE_cc_SCNR64_NL_HDR_ACDNR_Histo_CT.fit
https://www.dropbox.com/s/ihi21eekbmb00kl/LRGB_CT_Histo_Deconvolve.fit

And the linear files

https://www.dropbox.com/s/feh2u5j7p319i2b/MasterRed_r_crop.fit
https://www.dropbox.com/s/kwek7kumlmiv59f/MasterGreen_r_crop.fit
https://www.dropbox.com/s/fhnqet2bj1kw5mx/MasterBlue_r_crop.fit
https://www.dropbox.com/s/pfjmsovgfyqdor5/MasterLuminence_r_crop.fit


Thanks in advance for your help.

Shailesh Trivedi

[pfile]

what is the light pollution situation where these frames were captured?

it's very likely you need 10s of hours of integration time (!) to get good details if you are imaging in a high LP area. your integration time here is very short.

rob

[strivedi]

Rob,

Thanks for your suggestion. My conundrum is whether it is less integration time (I believe what you say is true, I have Bortle class 5+ worth of light pollution) or image processing workflow/skills. I think it is a combination of both.

For the first part, there is not much I can do except retake pictures with larger data sets at 10min and 20min each, which I will try when the clouds clear up here in Northern California.

For the second part, can you provide pointers? I am a newbie so a workflow with details would be helpful. The workflow from kayronjm seemed appropriate to me. I also tried the work flow by Vicent Peris on M33 at the link below

http://pixinsight.com/tutorials/M33-vperis/en.html


which isolates small scale & large scale structures and then recombines them. I did the steps very carefully but did not get a good image in the end.

I got better results with kayronjm's flow. Not sure if there is a better work flow to isolate the details in NGC7331.


Shailesh

[rockyraccoon]

Hi Shallesh,
you have an excellent setup that should yield much better data.
That image looks out of focus and there is some motion blur (stars are elongated). I would try to fix whatever is causing the defects in your starting FITs before you spend much time trying to process the defects out - or you'll end up spending hours and it's unlikely you'll be satisfied with the output. Also it's really important that you calibrate your frames with darks and flats especially if you want to tease out the finest structures in your images.
As Rob said your choice of sub length and number must be dictated by the quality of your sky.
I imaged NGC7331 last year from a "blue" zone and I only needed 8 x 20m to get a surprising amount of details in my image:
http://www.flickr.com/photos/dmal/10567452264/
You'd probably want to use shorter subs (but lots more of them) if you are imaging from a more light-polluted area. Where are you located in Northern California?

Good luck!


 

[pfile]

well, you may not be able to reach 10 or 20 minutes in your LP. here in oakland, at f/4.3 and 92mm i generally don't go beyond 300s for LRGB on bright targets, but i have sometimes been able to get up to 600s sub exposures on dim targets (m33 for example)

at any rate while processing low-SNR images build character, i find that high-SNR images almost process themselves. you can switch to narrowband imaging to get some really high-quality images. Ha is generally very bright and you'd be surprised how much faint signal you can capture with a good Ha filter and a mono camera.

rob

[rockyraccoon]

I guess I was trying to make the point that stars are fantastic (and unforgiving) "probes" that tell a lot about what is wrong (or right) with the original data. If a star is out of focus or elongated, so is the DSO in the frame.
Irrespective of sub length (which as you say is going to be sky-limited when shooting from inside city limits), in a pareto chart of factors that determine a final result, quality of incoming data matters IMHO a whole lot more than processing skills.
Switching to NB imaging is great advice. I would even go further and advise to stick to simply Ha (5nm, so as to include NII) to hone your skills. Color makes things a whole lot more complicated, and it's possible to create stunning BW images just by shooting Ha.

well, you may not be able to reach 10 or 20 minutes in your LP. here in oakland, at f/4.3 and 92mm i generally don't go beyond 300s for LRGB on bright targets, but i have sometimes been able to get up to 600s sub exposures on dim targets (m33 for example)

at any rate while processing low-SNR images build character, i find that high-SNR images almost process themselves. you can switch to narrowband imaging to get some really high-quality images. Ha is generally very bright and you'd be surprised how much faint signal you can capture with a good Ha filter and a mono camera.

rob

[jerryyyyy]

Looks like some of my Northern California light poluted images... we should start a support  group.  I live near Palo Alto...

I have been using 600s Lum but have just started experiment with 300s... I think I did this experiment once and found the 600s were better... I have the same camera as does Pfile.  Collect 10 at 300 and 5 at 600 and see which look better stacked....

I use 960 B and 750 for Red and Green.  My scope is a nasty old C8... f6.3 with the reducer. 

When I was learning how to do this Pfile suggested I needed at least 10h of images to get anywhere... I think that was an underestimate.  BTW, also not all galxies are created equally... M101 has tons of signal.  Good place to start. 

BTW2, you gotta get good flats.  This is actually easier than you think.  I just use Maxim DL's "Sky Flat Assistant" plug in and shoot them at sunset.... bomb proof.  I find that I need to reshoot them every few months as my filters, thought there are supposed to be sealed, still pick up crud. 

[jkmorse]

love the idea of a support group, but it will need lots of sub-chapters since there are so many areas where we just need a hug.  Light pollution, weather, the moon (damned orb) and my personal favorite, finally getting to the new moon, driving to get some dark skies and the damn clouds kill everything so you get all three.

On targets, agree that if you are starting out, 7331 is not the place to be.  That is a demanding task.  Took a serious upgrade in equipment, nice dark skies and a night's worth of iterations before I got an image I was happy with.  The Messiers are a much better place to get your feet wet and are so much less frustrating when starting out.

[jerryyyyy]

This was 17h exposure of M101 from Palo Alto:



This was 21h on NGC7331:



Both could be better processed now... but this is a lot of time over target...

[strivedi]

All,

Thanks for all the discussion and inputs in this thread. After spending several more hours over the last week or so with various options trying to eek out the spiral arms of NGC7331, I have come to the same conclusion as PFILE (Rob) originally suggested.

Which is that I have insufficient signal (actually only about 150 minutes worth) from my light polluted backyard in Folsom, CA. The max useful exposure was about 300s (RGB), since I got almost the same information from a 600s (L) exposure as well.

Rockyracoon I looked at your mono image on flickr, it has amazing detail, bravo, job well done. I know Blue Canyon has much darker skies than in Folsom, which is where I am. I am not sure why my stars seem out of focus to you, each time I take great pains to use Focusmax before I begin imaging. I know I have not taken flats. In any case there should be no motion blur, maybe the seeing was not that good that night.

I have other images taken with Ha, OIII, SII filters with upto 1200s exposure each which are a lot "brighter" as suggested.

Alas some objects like NGC7331 will be out of reach for me unless I spend several nights at a dark sky site. Or maybe I may get some clearner signal with NB filters.

Shailesh Trivedi