Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Galaxies, Light Pollution and CMOS Imaging

  • Please log in to reply
11 replies to this topic

#1 Seanem44

Seanem44

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1944
  • Joined: 22 Sep 2011
  • Loc: Stafford, VA

Posted 23 March 2018 - 06:42 AM

I have some questions here and I know you all can answer them :)

 

We are in Galaxy season.  My ability to image is decreased by about 40% due to where my house and backyard sit.  My house pretty much blocks the entire Eastern sky for me.  The West is starting to look very blank as spring approaches, save for Galaxies.

 

I live in pretty much a Red Zone.  I have an Ha, along with LRGB filters.  The Oiii filter I am buying soon will be no help/useless.

 

Is imaging Galaxies out of the question with my ZWO 1600 given my light pollution?  M81 for me is pretty much right over the DC megalopolis. 

 

Or, (given the power of the 1600) are several 30 second or so images within the realm of possibility?

 

I don't want to stop imaging because of the loss of good nebulous targets in my view.  The Rosette is sinking faster and earlier in April.  But I also don't want to waste my time fighting substandard images if I can avoid it.

 

Still being very new to CMOS imaging, I am still learning what the 1600 is capable of and I defer to the collective wisdom and experience of you all.



#2 Destin1701

Destin1701

    Viking 1

  • -----
  • Posts: 662
  • Joined: 26 Feb 2014
  • Loc: Boston area, MA

Posted 23 March 2018 - 07:31 AM

Don't give up on 'em Sean.  Light pollution just keeps getting worse and at my house (orange zone) I'll soon be a red zone with things like they are.  Everyone likes to light up their yards at night, for what?  To keep the prowlers away?  Boy if all it took was for light to stop crime...

 

In any case, you'll be looking at more integration time to get your SNR up in light polluted skies and you'll have to deal with gradients from those lights.  DBE in PI can blast away at those gradients or GradientXterminator in PS.  Both do very well.  You might not want to practice all that on M81 - although it has a bright core the arms are notoriously difficult to process and it's generally a tough target in terms of nearby galaxies.  M51, M106, might be better if you have line of sight.  I'm continually amazed at what folks are doing in LRGB from red and white zones.  Just takes more time and patience but you can really get great images.

 

Destin


Edited by Destin1701, 23 March 2018 - 07:32 AM.

  • Shiraz likes this

#3 pyrasanth

pyrasanth

    Apollo

  • *****
  • Posts: 1178
  • Joined: 08 Jan 2016

Posted 23 March 2018 - 07:48 AM

The scourge of light pollution can be banished with lots of exposures- never give up! see my post https://www.cloudyni...-april-edition/ this was taken 4 miles from Birmingham International airport with heavy light pollution.

 

As you know narrowband won't help with galaxies but great for gaseous nebula.



#4 Seanem44

Seanem44

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1944
  • Joined: 22 Sep 2011
  • Loc: Stafford, VA

Posted 23 March 2018 - 07:51 AM

The scourge of light pollution can be banished with lots of exposures- never give up! see my post https://www.cloudyni...-april-edition/ this was taken 4 miles from Birmingham International airport with heavy light pollution.

 

As you know narrowband won't help with galaxies but great for gaseous nebula.

I saw your post AND I just saw it in my digital edition of Sky at Night.  Why does the UK have so much better magazines than the US?

 

At any rate... I'm assuming that my usual NB 3 minutes at 200 gain won't suffice in Red LP.  Do you go much shorter?  Are we talking 30 seconds?  One minute? 



#5 baron555

baron555

    Mercury-Atlas

  • *****
  • Posts: 2558
  • Joined: 27 Sep 2010
  • Loc: Lockport, IL

Posted 23 March 2018 - 08:06 AM


 

Is imaging Galaxies out of the question with my ZWO 1600 given my light pollution? 

No, from the other thread (with the tables from Shiraz and commenting by Jon Rista) you know what gain and offset settings to use and what type of exposure lengths to use.

 

M81 for me is pretty much right over the DC megalopolis. 

To my north is Chicago and it doesn't stop me.

 

Or, (given the power of the 1600) are several 30 second or so images within the realm of possibility?

I run my 1600MM as follows:

Gain = 76

Offset = 15

Lum = 30 sec

RGB = 60 sec

Ha = 300 sec.

O & S = 200 sec

 

I imaged 20Lum, 5R, 5G, 5B and repeated all night at NGC 4565.  The subs being downloaded looked very promising.  About 8 hours in total.

 

I don't want to stop imaging because of the loss of good nebulous targets in my view.  The Rosette is sinking faster and earlier in April.  But I also don't want to waste my time fighting substandard images if I can avoid it.

 

Still being very new to CMOS imaging, I am still learning what the 1600 is capable of and I defer to the collective wisdom and experience of you all.

You'll never gain experience unless you image.  My setup is setup such that I can get it going and go to bed.  Sometimes something will bite me, but usually it works like a champ.  Rig #2b in my sig, lately just running unguided with the MX+.


  • Seanem44 likes this

#6 WadeH237

WadeH237

    Gemini

  • *****
  • Posts: 3478
  • Joined: 24 Feb 2007
  • Loc: Snohomish, WA

Posted 23 March 2018 - 08:38 AM

I am in an orange zone, right on the edge of red.

 

Here is the synthetic luminance for an image of NGC4565 that I am working on.  It was taken with 80 x 60 seconds each RGB, for 240 minutes total.  The camera is an ASI1600MM-cool and the scope is a Celestron EdgeHD 8 with F/7 focal reducer (this is first light for that combination).  It has plenty of color data, but I'm not done with that part of it yet.  Note that this is just a simple stretch in the early stages of processing.  It think that it's basically just had deconvolution done so far.

 

I would say to keep at it.

 

-Wade

 

NGC4565_synthetic_luminance.jpg


Edited by WadeH237, 23 March 2018 - 08:40 AM.

  • psandelle, Shiraz, Seanem44 and 1 other like this

#7 Shiraz

Shiraz

    Viking 1

  • -----
  • Posts: 571
  • Joined: 15 Oct 2010
  • Loc: South Australia

Posted 23 March 2018 - 08:43 AM

Hi Sean

 

the thing that matters is the contrast between a galaxy and the sky. That does not change with the sub length. Sure, CMOS chips allow short subs in which the sky has less signal, but so does the galaxy - so there is no improvement when we stack. CMOS doesn't help with LP.

 

Light pollution is a real pain, because, to overcome the shot noise from the sky, a longer overall exposure time is required and the final image may have color gradients due to spectral variations in the pollution. It isn't impossible, but it gets much harder as the sky gets brighter. Always worth a try though, particularly for brighter galaxies. EDIT: as Wade's image shows!

 

The other targets to maybe consider are the planetary nebulae. Some of those are quite bright and they can provide spectacular images from poor skies, particularly in narrowband. Then there are some quite beautiful asterisms and globular clusters that might be worth a shot.

 

cheers Ray


Edited by Shiraz, 23 March 2018 - 09:34 AM.

  • Seanem44 likes this

#8 pyrasanth

pyrasanth

    Apollo

  • *****
  • Posts: 1178
  • Joined: 08 Jan 2016

Posted 23 March 2018 - 08:56 AM

I saw your post AND I just saw it in my digital edition of Sky at Night.  Why does the UK have so much better magazines than the US?

 

At any rate... I'm assuming that my usual NB 3 minutes at 200 gain won't suffice in Red LP.  Do you go much shorter?  Are we talking 30 seconds?  One minute? 

I think you would be surprised to learn that the image you have looked at is 100 ten minute subs. The problem with short exposures, unless the gain is high, is that you initially capture more noise than signal. I find even under light polluted conditions that long exposures with moderate gain seem to suit me best. My conditions are not ideal. I have four sodium lights ringing my garden as well as a cone of light pollution from nearby offices and Birmingham Airport.

 

3 minute narrowband exposures are going to be far too short unless your system is exceptionally fast. I would try 20 minutes even under severe light pollution.


Edited by pyrasanth, 23 March 2018 - 09:03 AM.

  • psandelle and Shiraz like this

#9 bobharmony

bobharmony

    Vostok 1

  • *****
  • Posts: 157
  • Joined: 28 Oct 2017
  • Loc: Connecticut, USA

Posted 23 March 2018 - 08:59 AM

Sean - I say go for it.  I image from a couple of miles south of Hartford, but I think the end result after processing is worth the effort.  My individual subs are a brownish mess but they clean up nicely.  For my most recent example check out this link:

 

https://www.cloudyni...nother-version/

 

There were no really heroic efforts involved in producing this - just a quick pass through Star Tools followed by a Photoshop curves tweak.  The ST "Wipe" module does a decent job of cleaning out the gradients.

 

I have to agree that trying it out is your best course of action.

 

Bob



#10 bobzeq25

bobzeq25

    Voyager 1

  • *****
  • Posts: 13795
  • Joined: 27 Oct 2014

Posted 23 March 2018 - 09:04 AM

I image from a Red Zone, Bortle 7, mag per arc sec squared low 18s.

The keys are good gradient reduction in processing, and more total imaging time. Both essential. "Several" 30 second exposures are not going to work, you'd need at least 120.

Below is M81, only 1.2 hours due to conditions. 141X30", all told. 2 hours would have been better, 4 good, on this fairly bright target. Serious folks do 10 or more, imaging over multiple nights.

DynamicBackgroundElimination in PixInsight, maybe the best tool for gradient reduction (but there are others that work).

Fullsize here. https://www.astrobin...333099/?nc=user

M81 V2.jpg

Edited by bobzeq25, 23 March 2018 - 09:11 AM.

  • Vassar1978 and bobharmony like this

#11 rigel123

rigel123

    Hubble

  • *****
  • Posts: 15562
  • Joined: 29 Jun 2009
  • Loc: SW Ohio

Posted 23 March 2018 - 09:13 AM

I don't use a CMOS camera, rather a CCD but I don't think there is much difference when handling LP in a Red Zone.  I actually find galaxies easier in my Red Zone than reflection nebula, those create the biggest challenge for me in my Red Zone.  Oh, and dark nebula are nearly impossible, but then I haven't challenged myself with many dark nebula from my back yard.


  • bobzeq25 and Vassar1978 like this

#12 Jeff2011

Jeff2011

    Gemini

  • *****
  • Posts: 3381
  • Joined: 01 Jan 2013
  • Loc: Sugar Land, TX

Posted 23 March 2018 - 08:14 PM

It can be done Sean.  I live in a Bortle 8+ (white zone).  It takes a lot of integration time. I generally spend more time on LRGB than narrowband.   Also colors tend to be washed out compared to LRGB taken in darker skies but that comes with the territory.  Also you can’t get the faint parts to come out like you can in darker skies.  Here is one of my images taken with equipment comparible to yours.

 

get.jpg?insecure




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics