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LP Washout or Beginner Mistake?

astrophotography ccd imaging LP moon refractor
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#1 Mmarett

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Posted 11 November 2019 - 08:12 PM

Last night I completed one of my first imaging sessions and was pretty disappointed with the results. I tried to take subs of 20s, 30s, 45s 60s, 90s. The 90s subs were totally washed out and the 60s mostly were. I image on a parking garage in the downtown of one of the largest cities in the US. I have a LP filter but I wonder if my broadband setup is no match for the LP and full moon or if I am doing something wrong

 

Details:

Scope: Orion ED80

Auto Guider: Orion Starshoot 

Mount: Sirius EQ-G

Focal Corrector: Orion .85 Reducer and Corrector

Camera: QHYCCD 168C

Target: M31

Processing: PI

 

I blinked, debayered, aligned, stacked and stretched my images and they are terrible! The 90s image you couldnt even see the center of M31 hardly. Should I stick to 100s of 20s images or am I doing something wrong on my 90s subs? I attached some of the subs and the stacked image (mostly 20 and 45s subs). I haven't incorporated my darks, flats and bias because it seemed pointless after the initial processing. 

 

Stacked image is

 

20s Subs - 13

45s-  2

90s - 1

 

All other subs were terrible. I realize this is very little as far as subs go but I thought even a sinlge 90s sub would be better than the stacked image was. Something doesnt seem right. 

Thanks for all the help! 

Attached Thumbnails

  • 30sstretched2.PNG
  • 90sstretchedonly2.PNG
  • stackedM312.jpg

Edited by Mmarett, 11 November 2019 - 08:13 PM.


#2 Stelios

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Posted 11 November 2019 - 09:21 PM

I wouldn't expect much better imaging broadband with heavy LP and a full moon.

 

The color cast in the stacked image is probably from the filter, it should be possible to remove in PI.


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#3 17.5Dob

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Posted 11 November 2019 - 10:18 PM

Last night I completed one of my first imaging sessions and was pretty disappointed with the results. I tried to take subs of 20s, 30s, 45s 60s, 90s. The 90s subs were totally washed out and the 60s mostly were. I image on a parking garage in the downtown of one of the largest cities in the US. I have a LP filter but I wonder if my broadband setup is no match for the LP and full moon or if I am doing something wrong

 

Details:

Scope: Orion ED80

Auto Guider: Orion Starshoot 

Mount: Sirius EQ-G

Focal Corrector: Orion .85 Reducer and Corrector

Camera: QHYCCD 168C

Target: M31

Processing: PI

 

I blinked, debayered, aligned, stacked and stretched my images and they are terrible! The 90s image you couldnt even see the center of M31 hardly. Should I stick to 100s of 20s images or am I doing something wrong on my 90s subs? I attached some of the subs and the stacked image (mostly 20 and 45s subs). I haven't incorporated my darks, flats and bias because it seemed pointless after the initial processing. 

 

Stacked image is

 

20s Subs - 13

45s-  2

90s - 1

 

All other subs were terrible. I realize this is very little as far as subs go but I thought even a sinlge 90s sub would be better than the stacked image was. Something doesnt seem right. 

Thanks for all the help! 

To begin, your stacked image is only 16 subs, for 440 secs (7 min 20 sec) total exposure.......(barely enough for stacking to even work)....I have taken single 7 min subs on several occasions, but I still stack 25-35 of them . Even from a modestly light polluted site, you need to think in hours of total time, not seconds. Next time, I'd try for a bare minimum of 2 hrs total, 360 X 20"....

But to be realistic, I image from an "OK" dark site, good but not "great", but it's still 5 magnitudes darker than the worst inner city LP. To get the same SNR from the inner city you need to shoot 100X times longer total exposure. I always try for 2 1/2 to 3 hrs minimum at my dark site. To get the same results in your LP, you would need 250- 300hrs total exposure, which would require 45,000 to 54,000, 20" subs.....

 


Edited by 17.5Dob, 11 November 2019 - 10:36 PM.

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#4 J Davis

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Posted 11 November 2019 - 10:31 PM

Yep your total exposure time is pretty low.  Before trying to stack I would be trying a min of 30 to 40- 120 second exposures.  I shoot from a polluted area as well, but you can get some nice shots.  Again think in the range of hours of total exposure time. Even in fairly dark sky sites I shoot for 4-8 hours total on a single subject with 300 sec subs.

 

Just keep at it, the learning curve on all this is steep.

 

Jeff


Edited by J Davis, 11 November 2019 - 10:33 PM.


#5 Galaxyhunter

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Posted 11 November 2019 - 10:34 PM

Last night I completed one of my first imaging sessions and was pretty disappointed with the results. I tried to take subs of 20s, 30s, 45s 60s, 90s. The 90s subs were totally washed out and the 60s mostly were. I image on a parking garage in the downtown of one of the largest cities in the US. I have a LP filter but I wonder if my broadband setup is no match for the LP and full moon or if I am doing something wrong

 

Details:

Scope: Orion ED80

Auto Guider: Orion Starshoot 

Mount: Sirius EQ-G

Focal Corrector: Orion .85 Reducer and Corrector

Camera: QHYCCD 168C

Target: M31

Processing: PI

 

I blinked, debayered, aligned, stacked and stretched my images and they are terrible! The 90s image you couldnt even see the center of M31 hardly. Should I stick to 100s of 20s images or am I doing something wrong on my 90s subs? I attached some of the subs and the stacked image (mostly 20 and 45s subs). I haven't incorporated my darks, flats and bias because it seemed pointless after the initial processing. 

 

Stacked image is

 

20s Subs - 13

45s-  2

90s - 1

 

All other subs were terrible. I realize this is very little as far as subs go but I thought even a sinlge 90s sub would be better than the stacked image was. Something doesnt seem right. 

Thanks for all the help! 

But that is the first step &  a MAJOR part of processing.



#6 17.5Dob

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Posted 11 November 2019 - 10:49 PM

To give you a glimmer of hope, this was one of my very first AP's, from a bright Red/White zone. Unguided, 30" exposures, 55 X 30"...

Collecting the data is the "Easy" part.....learning how to post process it is 90% of the work.


21364234496_7b785f7c98_b.jpg


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#7 mewmartigan

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Posted 12 November 2019 - 09:25 AM

As others have said, the stack is only 7 minutes so you won't see much.

 

On your stacked image, just run Automatic Background Extractor (ABE) in Pixinsight with all the default settings and it should clean that up. It's from the 2 green pixels to every 1 red and blue on the bayer matrix. 

 

After you run ABE you can apply a ScreenTransferFunction (the button that looks like a radiation hazard to me) just to see what is there.


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#8 Mmarett

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Posted 13 November 2019 - 03:20 PM

Thank you guys I will try and do longer exposures next clear night. Thanks for the additional motivation!

#9 bobzeq25

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Posted 15 November 2019 - 01:06 AM

Last night I completed one of my first imaging sessions and was pretty disappointed with the results. I tried to take subs of 20s, 30s, 45s 60s, 90s. The 90s subs were totally washed out and the 60s mostly were. I image on a parking garage in the downtown of one of the largest cities in the US. I have a LP filter but I wonder if my broadband setup is no match for the LP and full moon or if I am doing something wrong

 

Details:

Scope: Orion ED80

Auto Guider: Orion Starshoot 

Mount: Sirius EQ-G

Focal Corrector: Orion .85 Reducer and Corrector

Camera: QHYCCD 168C

Target: M31

Processing: PI

 

I blinked, debayered, aligned, stacked and stretched my images and they are terrible! The 90s image you couldnt even see the center of M31 hardly. Should I stick to 100s of 20s images or am I doing something wrong on my 90s subs? I attached some of the subs and the stacked image (mostly 20 and 45s subs). I haven't incorporated my darks, flats and bias because it seemed pointless after the initial processing. 

 

Stacked image is

 

20s Subs - 13

45s-  2

90s - 1

 

All other subs were terrible. I realize this is very little as far as subs go but I thought even a sinlge 90s sub would be better than the stacked image was. Something doesnt seem right. 

Thanks for all the help! 

You have a difficult situation, but...

 

Under a full moon imaging anything other than a star cluster is pretty futile.  For anyone.

 

I image in light polluted skies, Bortle 7, mag per arc sec squared low 18s.  What you see on the stack is correct.  You fix it with gradient reduction in processing.  Example below.  It's shows simply one pass of ABE in PI, using only a ScreenTransferFunction to visualize the images.  You must change the default correction from none to subtraction.  Otherwise ABE does nothing (PI can be pretty idiosyncratic).

 

The fact that my background is blue instead of green has no significance.

 

You set exposure by computing the average value of a sub in electrons (PI gives data numbers or adus <same thing>).  Compare it to the read noise of your camera squared.  It should be between 5 and 10X that number.

 

Then shoot more subs.  Total imaging time is crucial in light polluted skies.  You did about  9 minutes, way too little.  My rule of thumb is 1 hour minimum, two is better, 4 is good.

 

Bias, flats, and darks are necessary,  For one thing is, if you omit them, you'll almost certainly learn bad habits in processing.  Processing is hard enough without having to unlearn bad habits.  <smile>

 

The LP filter is useless on galaxies.  It can work some on emission nebula, but has drawbacks.  I basically don't use one, even on emission nebula like that below.  You can see the results on my astrobin, although some emission nebula images used narrowband filters, which are light pollution filters that work (on emission nebulae).

 

ABE exampl before.jpg

 

ABE example after.jpg


Edited by bobzeq25, 15 November 2019 - 01:23 AM.



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