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A soso NGC4236

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#1 Mert

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Posted 25 March 2019 - 04:23 PM

Hi all,

 

I couldn't resist seeing a clear sky and setup on my 

balcony again.

The seeing was rather good, but the sky looked a bit greyish

against the skyglow of Pamplona.

My guiding, as usual, not the best there is.

Here is an integration of 45 frames of 180 seconds binned 2x2

with the RC8 at native focal length and the ASI1600MCC at -15ºC.

Ah, and I also used the IDAS LPV4 filter to suppress the light polution.

I hope to be able to get under darks skies sometime!

From this galaxy I haven't seen many images, maybe 

because of it's low surface brightness??

Tips and/or tricks welcome to get this target well exposed!

 

Thanks for looking,

Mert

Attached Thumbnails

  • NGC4236-032419-45x180-RC8-IDAS-balcon-APP-CN.jpg
  • PHD2.jpg

Edited by Mert, 25 March 2019 - 04:25 PM.

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#2 bobzeq25

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Posted 25 March 2019 - 04:50 PM

Tips.

 

First suggestion is to remove the light pollution filter.  It's not doing you much good on a galaxy, and it's blocking a significant amount of data, extending both subexposure times and total imaging time.

 

ABE or (requires more skill) DBE, can reduce the effective light pollution well, and, unlike LP filters, they work just as well on galaxies.   Did you do one or both of those?

 

Then, you likely could do 90 X 90", and still get increased signal. 

 

Next, consider a reducer.  Your image scale is about 1.0 arc sec squared per pixel.  A 0.8X reducer would move that to about 1.2.  Your skies would have to be awfully steady for 1.0 to be noticeably better, and you could get more signal, lower exposure, and get better signal to noise ratio, while not having any serious loss of resolution.

 

That image suffers mostly from poor signal to noise ratio, so that's where you should concentrate your efforts.

 

Did you do flats, darks, and dark flats?


Edited by bobzeq25, 25 March 2019 - 04:52 PM.

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#3 twidget

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Posted 25 March 2019 - 08:57 PM

Mert,

 

For just over 2 hours of integration, that is a fairly decent image, IMHO smile.gif . I think you are correct; since it is a low-surface-brightness object, viewed obliquely from Earth, it doesn't seem to attract very much attention from AP folks.

 

For what it's worth from a relative newbie, I agree with bobzeq:

 

Tips.

 

First suggestion is to remove the light pollution filter.  It's not doing you much good on a galaxy, and it's blocking a significant amount of data, extending both subexposure times and total imaging time.

 

ABE or (requires more skill) DBE, can reduce the effective light pollution well, and, unlike LP filters, they work just as well on galaxies.   Did you do one or both of those?

 

That image suffers mostly from poor signal to noise ratio, so that's where you should concentrate your efforts.

 

Did you do flats, darks, and dark flats?

DBE (I use DBE rather than ABE, if possible) WILL work wonders with LP; I use it on every image since I deal with moderate or worse LP all the time. It isn't hard to learn, just takes practice (and more practice, and then........more practice). Also, make as many runs with DBE as it takes to remove the gradients. I thought of getting a good LP filter, but decided to just get good at DBE, instead. 

 

I've got some N4236 subs (10x480s lums) from a mono Orion G3, taken almost 2 years ago when I had only 6 months AP experience, that I will work up in PI, with and without DBE, and put up for you to compare with yours (the image WILL NOT be anywhere as good as yours), to give you an idea what you should be able to get with your gear without a LP filter.

 

Clear Skies!

 

Mike


Edited by twidget, 25 March 2019 - 09:00 PM.


#4 twidget

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Posted 25 March 2019 - 10:19 PM

Mert,

 

N4236, 5May2017, single 480s lum, mono G3 camera, no LP filter, 8" visual newt, raw, PI auto-stretch:

 

NGC4236 050517 480s_3 AutoStr.jpg

 

 

 



#5 twidget

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Posted 25 March 2019 - 10:22 PM

N4236, 5May2017, stack of (all) 10x480s lums, dark-calibrated (no bias or flats), no DBE, PI auto-stretch:

 

NGC4236 050517 480s PIXsf AutoStr.jpg

 

 



#6 twidget

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Posted 25 March 2019 - 10:40 PM

N4236, 5May2017, stack of (all) 10x480s lums, dark-calibrated (no bias or flats), 7 passes of DBE, PI auto-stretch:

 

NGC4236 050517 480s PIXsf Db7 AutoStr.jpg

 

It isn't very apparent from the auto-stretched JPEGs, but the LP which is present in the 1st stacked image is gone in the DBE'ed stack image (though the dark current and flat-correctable glow that was not removed due to lack of those cal frames is still there but lessened). Also, no noise reduction in any of the JPEGs.

 

The point is, without using your LP filter, but with the use of DBE (or ABE) in PI, you should be able to obtain a MUCH brighter image than the one you posted at the top of the thread, with the eqpt you used. The G3 is actually a pretty decent little starter cam (approx. 0.5 megapixels), but nowhere near the quality or ability of the ASI1600. So, as bobzeq25 suggested above, try it without the filter, and use ABE or DBE in your processing instead. You'll be surprised smile.gif .

 

I hope this helped, and I eagerly await your next N4236 image, sir !!

 

Clear Skies !!

 

Mike


Edited by twidget, 25 March 2019 - 10:41 PM.

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#7 Mert

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Posted 26 March 2019 - 12:54 PM

Wow, a lot of useful response here, first thanks to all!!

 

Now @bobzeq25 : Hi Bob, thanks for your suggestions, I was imaging

at 0.96" per pixel, and didn't want to use the reducer in order to get a bit

closer to the galaxy. Normally, when imaging from my balcony, I have to

fight light polution, facing straight towards Pamplona city lights.

I also use a Triad filter sometimes but then the color information is not

so great, however it produces a very nice black background.

For targets without much Halfa not so good.

In the conditions I was imaging, color information is easily washed

out by the greyish looking sky.

I will try without polution filter and only use UVIR block filter, maybe trying

as you said 90 x 90"

By the way, I did use Flats, Darks and Bias's and used ABE a couple of times

and also Neutralize Backgeound and so on.

 

@Mike: Thanks for your input, I typically use either DBE or ABE as per

the image among quit some other tools.

Also inside of AstroPixelprocessor I can do lightpolution removal

quit efectively.

Your images seem to have more signal, do you image from a dark site??

When looking to the sky from my balcony it alsmost loos like my flat panel!

A bit darker but grey!

An estimate of the NELM would be 4,5 to 5 at excepcional dark nights

without Moon or Footbalstadium lights.

 

Again, thanks for your input, much apreciated!!

Mert


Edited by Mert, 26 March 2019 - 12:56 PM.


#8 twidget

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Posted 26 March 2019 - 02:31 PM

Mert,

 

My apologies, I assumed (incorrectly) that you might not be using ABE/DBE. 

 

     No, I do not image from a dark site. I shoot from my back yard, with houses on all sides of me no more than 100'-200' (30-60 meters) away, 4 streetlights within that same area, only 1/2 mile (0.8 km) from the downtown district in a town of 45,000 people. My LP is sometimes horrendous, usually bright enough to read the headlines of a newspaper. (9-10 on the Lorenz scale, where 13 is the worst). And, being in town, I often have to deal with heat-island clouds. So I'm no stranger to LP. 

     Those images I put up were taken with an Orion G3, a mono CCD camera with large 8.6um x 8.3um pixels, so it yields much higher SNR for a given exposure length than my 1600 does (at least I think that is why). N3246 is on my springtime 1600 target list, so I will be able to directly compare to the G3 images.

     I use a ZWO luminance filter (I think it is the same as UV-IR) with the 1600, but I don't believe I used any filter with the G3 for the images above.

 

Mike    


Edited by twidget, 26 March 2019 - 02:39 PM.


#9 Mert

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Posted 26 March 2019 - 03:20 PM

Thanks Mike, I still see I get much less signal with my 1600!

 

At the moment I setup on the balcony again, this time with a UV/IR

block filter and shooting 2 x 2 binned at 60 seconds.

The images are totally washed out, after DBE/ABE I can just see

some of the glaxy, not near anything like your single frame!

The sky looks grey to whitish and I can perfectly see the houses

against the sky!

No problem, with aprox. 120 frames of 60 seconds I'll get

some signal in and also less problems with autoguiding ( I hope )

 

Mert


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#10 Mert

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Posted 26 March 2019 - 04:07 PM

Oh well, things are much worse then with the light polution filter!

Now I capture hardly anything else then skyglow!

We'll see if there is anything useful, next time I try to get out

to the mountain far away from the city lights!



#11 twidget

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Posted 26 March 2019 - 04:35 PM

Mert,

 

     Here's a couple of JPEGs of NGC3184, a mag 9.8, 22.7 surface brightness, galaxy (similar mag to N4236) from 12Feb2019, shot with my 1600, 120s lum, gain 200, UV-IR (luminance) filter. Both are untouched (raw).

 

No stretch:

 

NGC3184 021219 120s-20d200g RAW 0.25.jpg

 

PI auto-stretch:

 

NGC3184 021219 120s-20d200g Str1 0.25.jpg

 

This is a face-on fuzzy. As you can see, even at 120s it is quite dim, and the LP in the sub is bright (except where the vignetting reduced it).

 

Don't worry, if your focus/tracking/etc are good, a 120x60s stack processed well should give you a good stacked image smile.gif

 

I'm getting ready to shoot, also. The first good moonless (at least till 2am local) night for me in 2 months cool.gif

 

Mike


Edited by twidget, 26 March 2019 - 04:36 PM.


#12 twidget

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Posted 26 March 2019 - 04:53 PM

Mert,

 

Here is a JPEG of the stacked image (30x120s), PI autostretched, subs fully preprocessed, image cropped, and 5 passes of DBE. Nothing else done to it.

 

NGC3184 021219 120s-20d200gL AStr 0.33.jpg

 

Your N4236 image from this session should be of similar brightness (unless being from OSC cam makes a difference), since you will integrate 2 hours (of 60s subs), and I integrated 1 hour (of 120s subs).

 

Clear Skies!!

 

Mike


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#13 Mert

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Posted 26 March 2019 - 05:23 PM

Hi Mike, yes you are right, mine is a OSC!!

 

I just stopped since I also messed up with my focus, don't have

my day :shrug:

Next time better, but thanks a lot for your example frames, that

helps!!

 

Regards and good session!!

Mert



#14 Mert

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Posted 26 March 2019 - 05:51 PM

Just for laughs, here is a single frame, with the UV/IR filter,

as you can see, nice light polution apart from the rubbish

on the filter etc.

Lateron the processed "image" from 78 frames, let's see

what I can make out of that crap.

 

 

Attached Thumbnails

  • NGC4236-1x60-bin2x2.jpg


#15 twidget

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Posted 26 March 2019 - 07:16 PM

Yes, "nice" LP wink.gif ! Good luck on the processing, Mert! 



#16 bobzeq25

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Posted 27 March 2019 - 01:50 AM

If you can measure your light pollution with this method, people can help better.

 

https://www.pbase.com/image/37608572



#17 Mert

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Posted 27 March 2019 - 08:29 AM

A very interesting article but it is written for DSLR I'm afraid.

I have a spreadsheet where I can try to measure what I've got,.

A sad story that the sky at my balcony looks like my flat panel ( almost ) tongue2.gif



#18 twidget

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Posted 27 March 2019 - 09:59 AM

Maybe you need a darker flat panel? rofl2.gif 

 

Just kidding (or am I???) smile.gif

 

Mike


Edited by twidget, 27 March 2019 - 10:04 AM.


#19 twidget

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Posted 27 March 2019 - 10:10 AM

Mert,

 

Also helpful for folks to assist you would be your other settings, such as OSC gain and offset.

 

To me, your description of the LP reminds me of the HTS (high thin s*** - stuff-, aka cirrus clouds) that I have move in probably 60% of the time on otherwise good shooting nights, after midnight.

 

Mike


Edited by twidget, 27 March 2019 - 10:16 AM.


#20 Mert

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Posted 27 March 2019 - 01:55 PM

Hi Mike,

 

Good joke lol.gif

I'd like to get an absolute dark panel for that :waytogo:

 

If I'm not wrong, the sky lately doesn't look dark blue when

there are no clouds, but more like a milky whitish blue.

Today when the sun set, there was some sort of halo around it

indicating a huge amount of water vapor if I'm not mistaking.

 

Likely tonight I go for another failing session this time either

with the UVIR filter ( doesn0t work here ) or with the Triad going

for some easy target, at least I'm busy with astronomy and

will try to get focussing better under control.


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#21 twidget

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Posted 27 March 2019 - 02:16 PM

Mert,

 

     I like to observe jet aircraft contrails in the hours before dark.....if the contrails are short, that indicates a relatively low amount of water vapor at the jets' altitude (6-10 km, maybe). If the sky is full of long contrails, you will most likely be dealing with worse LP and poor transparency during the imaging session.

 

Hope you have better luck tonight. My night last night started out with so-so seeing and good transparency with decent tracking, and progressed to great seeing and below-average transparency with great tracking by the time I quit at 4am (when the last-quarter moon was about 30 deg above the horizon and messing up the subs). Best seeing I've had since early December.

 

Mike


Edited by twidget, 27 March 2019 - 02:17 PM.


#22 Mert

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Posted 27 March 2019 - 03:23 PM

Ha, that sounds good Mike, I think the contrails were quit long :-(

tonight before sunset.

Anyway, I swapped the filter for the IDAS LPV4 filter and now shooting

at M109, in a single frame I can just see the central bar and some of the

arms. ( once loaded into Pix, background subtracted and Screentransferred ).

Let's get some 30 or 60 frames.

Maybe lateron ( can't make it late since I get up early to go to work ) I

will get some frames on NGC4236 again just to compare what the UVIR

filter gives and the IDAS LPV4.

IMHO the IDAS does way better job here on my balcony.

I don't have a wide view from here since it is a very small bañcony just

between 2 rather high walls so I am limited almost straight to the north

+- 15 degrees or alike.



#23 twidget

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Posted 27 March 2019 - 03:46 PM

Mert,

 

That's a good sign, to be able to see that on M109, in a single frame. What gain setting are you using?   Yes, the comparison subs for N4236 is a good idea. "Ouch" on the narrow balcony FOV undecided.gif Time for a trip to the mountain???

 

Mike


Edited by twidget, 27 March 2019 - 03:47 PM.


#24 Mert

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Posted 27 March 2019 - 06:28 PM

I'll post tomorrow, I just took a couple of frames on NGC4236 as well.

Finished packing up, I have taken 60 frames on M109, let's see

what I can get out of that!

Gain used is 139 ( unity gain ) and offset is 10 ( I think ), anyway these

are the default values from the Ascom driver.

Also took Flats, I already have a Dark and Bias library.

This time I went for 120 seconds per frame.

 

Mert


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#25 Mert

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Posted 28 March 2019 - 01:01 PM

Ok, as promised, here are the 2 images taken with binning 2x2, 60

seconds each with the RC8 at F8, the first one with the UVIR filter,

rather noisy!!!

The second one with the IDAS LPV4 filter much better but less of

the galaxy!

Both are just screentransfer streched, nothing more.

 

Here goes the first ( UVIR ) then the second one ( with IDAS LPV4 )

 

 

Attached Thumbnails

  • NGC4236-1x60-bin2x2 RC8 UVIR.jpg
  • NGC4236-1x60-bin2x2 RC8 IDAS.jpg

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