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How to pull out more DSO

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#1 castorpolu11

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Posted 25 September 2021 - 03:02 PM

I'm looking for advice from some of you EAA veterans on increasing visibility of DSO's.

 

I've had some moderate success with EAA in my bortle 6 neighborhood and I'm eager to improve my skills and setup. Lately I've noticed that when I attempt to observe nebula I get a wonderful, sharp image of stars tightly focused but no nebulosity at all. I use a 152mm f/5.9 with IR/UV cut filter and a 80mm f/7 unreduced. I control the setup with live stacking on the ASIAir pro. I've also used Sharpcap in the past but I do not plan to switch back to it. 

 

I've tried with both a asi385mc and also my unmodified Nikon D5100. I have confirmed that my goto's are centered. I've played around with sub time and it has not made much difference. I have a few ideas but I'd like some feedback before I take my next step. I am considering:

  • Experimenting with a light pollution filter. I have a L Pro that I can use with the asi385 
  • Adding a L Extreme to the train
  • Modifying the Nikon

Any advice on the likelihood that any of those strategies might improve my EAA views of DSO would be welcome. Thanks!



#2 steveincolo

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Posted 25 September 2021 - 03:16 PM

For emission nebula from my deck (Bortle 5 optimistically) I've started using an L-Extreme.  Here are a couple with my TV-85 and 0.8x reducer from the day after full moon earlier this week.  Gain 360, 10 second subs x 20-30 exposures, not much total integration time.  

 

NGC 6960
 
 
NGC 7635
 
[Edit] This is using the ASIAIR Pro.  I start with the Auto stretch, then turn it off, expand the left side of the histogram using the "+," setting the black point to the hump, and then aggressive use of the mid point to show the nebula.  

Edited by steveincolo, 25 September 2021 - 04:21 PM.

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#3 alphatripleplus

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Posted 25 September 2021 - 03:31 PM

What gain are you using with your ASI385MC, and what typical total exposures? Also what targets are you looking at that are not showing nebulosity, and are you using the AutoStretch feature in the ASIAIR Pro? 



#4 GazingOli

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Posted 25 September 2021 - 04:12 PM

Like Errol is asking for the settings and the stretching I can show one examples of how to get the nebulae on screen:

 

M 20 with the CPC800, just 8 s subs after some minutes stacking with SharpCap. Gain was 400, camera ZWO ASI 294 MC uncooled. The important thing is the position of the sliders in the histogram. Put the mid level slider to the right and you will see nothing of the nebula anymore.

 

exampleM20 C8f6.3ASI294UH screen2.jpg

 

I used a simple broadband UHC filter, even a UV/IR or no filter at all would do.

 

However the Veil nebula is a very faint object and not so easy to capture.

 

CS.Oli


Edited by GazingOli, 25 September 2021 - 04:15 PM.

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#5 castorpolu11

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Posted 25 September 2021 - 06:23 PM

Thanks for the feedback this is great!

 

My typical sequence is 10min total at 10sec subs. 

 

I have played with the histogram but I have some learning and fine tuning to do in that area. Is the mid level slider roughly equivalent to the slider on the right in the ASIAir histogram?

 

 

I've started using an L-Extreme

Those pics are awesome! I'd be super happy with that kind of result. Do you credit the filter as an important part of your setup for those kinds of targets?

 

 

expand the left side of the histogram using the "+," setting the black point to the hump

Can you post a screenshot of where you're setting it? I usually like it a bit to the left of the hump. Are you suggesting placing it right at the crest?

 

 

what typical total exposures

Usually about 55 over 10min or so. I have tried different sub lengths but rarely run the sequence for more than 10min.

 

 

 

then aggressive use of the mid point to show the nebula

Does this mean moving the slider on the right to the left towards the hump? When I've done this I've only noticed the whole picture lightens but I have not seen the nebula teased out yet. 

 

 

What gain are you using with your ASI385MC

I have left it on the middle setting which is 170. Sounds like I could benefit from trying it higher is that right?

 

 

1000x thank you for the suggestions!



#6 castorpolu11

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Posted 25 September 2021 - 06:32 PM

Regarding targets I've been able to get some decent shots of M27 and the lagoon but as I browse the suggested target list for the ASIAir or try some of the monthly challenge targets I've been striking out. I have framed some of them ahead of time so I think they should be there but I'm missing something in terms of drawing out the nebula. 



#7 GazingOli

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Posted 25 September 2021 - 06:34 PM

I did not use ASI AIR so far, so I cannot tell if the histogram controls are the same.

 

In ShapCap put the black level slider to the peak of the histogram and move the mid level to the left to enhance the contrast. You can usually see the nebula then, even if it might look not very nice. Just level it out as best. Forget the white level or leave it to the left corner.

 

The rest is a little bit of experience. Exposure, gain and offset and the control of the sliders in the histogram, which can vary a lot, depending on the object.

 

CS.Oli



#8 alphatripleplus

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Posted 25 September 2021 - 10:29 PM

 

 

I have left it on the middle setting which is 170. Sounds like I could benefit from trying it higher is that right?

 

 

 

For EAA with that camera, I would suggesting using a high gain (around 300-350); also  read noise bottoms out around 350.



#9 steveincolo

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Posted 26 September 2021 - 01:01 AM

I think you can try the other suggestions you're getting from Oli and Errol before trying a filter.  For the Iris Nebula, which is a reflection nebula, I didn't use a filter.  Here's a sequence to show how I stretched it in the ASIAIR app.  Notice how little you can see of the nebula using the auto stretch.

 

IMG 2296
 
IMG 2297
 
IMG 2298
 
IMG 2299
 
And not just nebulas!
 
IMG 2302
 
IMG 2303
 
Using a really extreme stretch, I could make out the Crescent Nebula without the L-Extreme.  Here it is without and with.
 
IMG 2306
 
IMG 2308

 

Although the right slider has a white triangle, it wouldn't have made much sense for ZWO to make it the white point, as Oli points out.  I'm guessing it's for the midpoint, but I could be wrong.  

 

These are all with a C6 and 0.63x reducer.  I'm using a ASI533MC, which has similar QE and pixel size to your ASI385MC.  But your camera has even lower read noise at high gain, as Errol noted.  I used 360 gain with the filter and 200 gain without in these images.

 


Edited by steveincolo, 26 September 2021 - 01:11 AM.

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#10 alphatripleplus

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Posted 26 September 2021 - 07:14 AM

For EAA with that camera, I would suggesting using a high gain (around 300-350); also  read noise bottoms out around 350.

By combining a high gain setting that happens to coincide with the lowest read noise (well under 1e-) you will potentially pick up the faintest details in the shortest time. Worth trying.



#11 dave85374

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Posted 26 September 2021 - 06:59 PM

Steve,

 

Looking at your histogram, are you clicking on the X on the right side.  Normally when I click on that X inside the circle your histogram changes in that the hump gets bigger/taller or whatever you want to call it and you have more movement in the slider so you have greater control of the slider instead of just 1/4 to 3/8 of an inch.  I will or should look something like the example below only the lines will be connected the whole way from one side to the other.  You do get a lot more control of the histogram this way.  I only found about the X inside the circle about a month ago from someone else out here.  You get the same result if you look at your fits files in the ASIStudio which you can download from ZWO.

 

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#12 steveincolo

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Posted 26 September 2021 - 08:06 PM

Steve,

 

Looking at your histogram, are you clicking on the X on the right side.  Normally when I click on that X inside the circle your histogram changes in that the hump gets bigger/taller or whatever you want to call it and you have more movement in the slider so you have greater control of the slider instead of just 1/4 to 3/8 of an inch.  I will or should look something like the example below only the lines will be connected the whole way from one side to the other.  You do get a lot more control of the histogram this way.  I only found about the X inside the circle about a month ago from someone else out here.  You get the same result if you look at your fits files in the ASIStudio which you can download from ZWO.

 

                                                  _______________--------------___________

                             _____---------                                                                    --------------__________

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You mean the + inside the magnifying glass, right?  I am using it.  Check out the sequence in the first four images I posted.  Glad you found it too, it’s critical to getting a good stretch. 




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