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An ASI1600 high gain experiment - Bubble Nebula

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#26 Jon Rista

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Posted 08 September 2016 - 10:16 PM

Dkeller, I'm glad you are giving it a try. It's very interesting, the capabilities of this. I am imaging CTB-1 right now. It's an extremely faint object, although I don't think as faint as OU4. I know it's been a challenge for people in the past. So far, with 120s Gain 200 subs, I'm seeing it in each individual sub. I expected going in that I might have to stack first to see anything, but it was right there without any fuss. Now I am particularly excited to give OU4 a try. It's both faint, and OIII, which is kind of a one-two punch combo in narrow band. 

 

Regarding offset. Changing it from 21 to 50 won't result in some huge difference. The main difference is the background....if you set it too low, you will usually see banding from the bias signal in the background. To see that in SharpCap, you gotta expand the Display Controls panel, crank Display Contrast up to around 8, and Display Gamma to maybe 1.3. Then start fiddling with offset (which is the Brightness setting). You should see what I am talking about. 



#27 Gary Imm

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Posted 08 September 2016 - 10:26 PM

Yes, it's fun to test the capabilities of this camera.  I was able to barely image the soap bubble in less than an hour of stacked Ha integration, although I couldn't really see it on any of the 5 minute subs. 

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#28 dkeller_nc

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Posted 08 September 2016 - 10:41 PM

Dkeller, I'm glad you are giving it a try. It's very interesting, the capabilities of this. I am imaging CTB-1 right now. It's an extremely faint object, although I don't think as faint as OU4. I know it's been a challenge for people in the past. So far, with 120s Gain 200 subs, I'm seeing it in each individual sub. I expected going in that I might have to stack first to see anything, but it was right there without any fuss. Now I am particularly excited to give OU4 a try. It's both faint, and OIII, which is kind of a one-two punch combo in narrow band. 

 

Regarding offset. Changing it from 21 to 50 won't result in some huge difference. The main difference is the background....if you set it too low, you will usually see banding from the bias signal in the background. To see that in SharpCap, you gotta expand the Display Controls panel, crank Display Contrast up to around 8, and Display Gamma to maybe 1.3. Then start fiddling with offset (which is the Brightness setting). You should see what I am talking about. 

Thanks, I'll give it a try.  Looks like tonight will be an exercise in frustration, though.  I've actually gotten the Iris in Ha before with this filter, but for some reason or another I got nada on 15 stacked 120s subs at a 200 gain setting.  Not exactly sure why, but since it's a school night, I may have to pack it in and give it a try tomorrow night.  Still, and interesting experiment.



#29 Jon Rista

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Posted 08 September 2016 - 10:47 PM

Very interesting. If I am able to get enough data on CTB-1 tonight, I might switch to Iris and give it a try. Never considered trying Iris in NB because I thought it was all reflection, but if it's got some Ha, it's worth a try. ;)



#30 Jon Rista

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Posted 09 September 2016 - 12:38 AM

So, it's clear...but wow is it a crappy night. Bad seeing, terrible transparency, and a half moon. Guess it will make for a darn good test on CTB-1. I've stacked what I've acquired so far...35x120s gain 200 subs (1h10m):

 

rTMQAf7.jpg

 

For an ultra faint target, so far so good. I think I can acquire another three hours, so I am going for it. The stars are not as tight in this...but my guide RMS is just over 1", so it's no surprise. I usually see huge amounts of integrated exposure on this, with large scopes, huge sensors with huge pixels, and hours of very long exposures. So I don't think I'm doing too bad. 



#31 noisy

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Posted 09 September 2016 - 09:18 AM

I want to try this on the North America nebula/great wall this weekend in Ha for my first attempt at narrowband shots. Just being able to test multiple settings in one night because the exposures will be relatively short is more than I was hoping I could do... I don't get a lot of imaging time.



#32 dkeller_nc

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Posted 09 September 2016 - 09:31 AM

So here's a reference photo of the same object (Abell 85) by Don Goldman (Astrodon):

 

http://astrodonimagi...ernova-remnant/

 

He has quite the set-up, running near $100k for the scopes, cameras, mounts, etc... that definitely takes his work out of the "amateur astroimager".  But it'll be very interesting to see how close we can get with <$10k worth of equipment.



#33 FiremanDan

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Posted 09 September 2016 - 10:25 AM

I am eager to get clear nights and a fixed/working mount. 
I think this might be great for my C8 and things like planetary nebula, clusters and maybe even galaxies. 

Since I don't have the money for an OAG and worthy guide cam, this might be the solution. 
I wonder how this would look with my SV80 at 4.8 383mm FL on something like the North America Nebula or Horsehead Nebula. 



#34 telfish

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Posted 09 September 2016 - 11:01 AM

I am eager to get clear nights and a fixed/working mount. 
I think this might be great for my C8 and things like planetary nebula, clusters and maybe even galaxies. 

Since I don't have the money for an OAG and worthy guide cam, this might be the solution. 
I wonder how this would look with my SV80 at 4.8 383mm FL on something like the North America Nebula or Horsehead Nebula. 

 

 

Should work really well with your SV80 it's a little wider than Jon's lens and about the same at F4. You should not need guiding for that scope. Your C8 at prime you might struggle with getting under your unguided limit.



#35 Jon Rista

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Posted 09 September 2016 - 12:22 PM

 

I am eager to get clear nights and a fixed/working mount. 
I think this might be great for my C8 and things like planetary nebula, clusters and maybe even galaxies. 

Since I don't have the money for an OAG and worthy guide cam, this might be the solution. 
I wonder how this would look with my SV80 at 4.8 383mm FL on something like the North America Nebula or Horsehead Nebula. 

 

 

Should work really well with your SV80 it's a little wider than Jon's lens and about the same at F4. You should not need guiding for that scope. Your C8 at prime you might struggle with getting under your unguided limit.

 

 

Actually, it would be the inverse of that. ;P The SV80 has an 80mm aperture, which would gather the least amount of light. My 600mm f/4 lens has a 150mm aperture. The C8 has a 203mm aperture. The f/ratio (well, focal length) really tells you the magnification.

 

With the SV80, I bet 90-120s subs at gain 300 would be ideal. 



#36 FiremanDan

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Posted 09 September 2016 - 12:27 PM

I would guide on both OTAs. But doing 300s with my C8 was a pain. 

I can't even remember what gain I normally use. Unity, whatever that is. It's been so long since I have gotten to do anything. 



#37 telfish

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Posted 09 September 2016 - 12:29 PM

 

 

I am eager to get clear nights and a fixed/working mount. 
I think this might be great for my C8 and things like planetary nebula, clusters and maybe even galaxies. 

Since I don't have the money for an OAG and worthy guide cam, this might be the solution. 
I wonder how this would look with my SV80 at 4.8 383mm FL on something like the North America Nebula or Horsehead Nebula. 

 

 

Should work really well with your SV80 it's a little wider than Jon's lens and about the same at F4. You should not need guiding for that scope. Your C8 at prime you might struggle with getting under your unguided limit.

 

 

Actually, it would be the inverse of that. ;P The SV80 has an 80mm aperture, which would gather the least amount of light. My 600mm f/4 lens has a 150mm aperture. The C8 has a 203mm aperture. The f/ratio (well, focal length) really tells you the magnification.

 

With the SV80, I bet 90-120s subs at gain 300 would be ideal. 

 

  I was thinking of focal length at 383mm compared to your lens at 600mm. I though that would give Dan a wider field of view. Am I wrong?


Edited by telfish, 09 September 2016 - 12:30 PM.


#38 Jon Rista

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Posted 09 September 2016 - 12:50 PM

Oh, I thought you were talking about signal. The SV80, yes, it would give a wider FoV. 



#39 jlandy

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Posted 10 September 2016 - 06:59 AM

Quick question - how often are you dithering your subs? My astro computer seems fairly slow at saving captures, I'm wondering if I would actually lose total integration time over a night after accounting for dithering time and the computer dabbing twice as many shots 

 

Very interesting results though, I'm definitely considering dabbling with 200 gain



#40 jsardina

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Posted 10 September 2016 - 07:15 AM

Hello Jon,

 

    Great post and your images are stunning, Thanks for giving such detailed information as I also have a 1600 and am also testing the QHY 183c. I live in severely light polluted skies only being 15 miles west of Manhattan and 3 miles north of Newark, NJ I have to get very creative with filters and hope to someday get what your getting out of your scope.  

 

By the way I'm using my 14" Meade native F8 and my RC 10" native F8, I also reduce these two scopes but have only been able to get down to about F5.2 

 

Thanks again for this post,

Joe



#41 Jon Rista

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Posted 10 September 2016 - 12:54 PM

Quick question - how often are you dithering your subs? My astro computer seems fairly slow at saving captures, I'm wondering if I would actually lose total integration time over a night after accounting for dithering time and the computer dabbing twice as many shots 

 

Very interesting results though, I'm definitely considering dabbling with 200 gain

At the moment, I am doing everything manually. I have shelved SGP for now, in large part because of this very concern. SGP is very heavy-handed in the way it manages your sequence, and at the moment it forces a dither every frame. That would totally decimate my ability to use high gain effectively.

 

So right now, I am still using SharpCap, and still doing things manually. SharpCap is somewhat familiar to me, though, as it allows me to work similar to how I did before with BYE. It supports real time live view from the sensor, and that allows me to do things like focus in real time. I don't need a bhatinov mask, I don't even need an FWHM meter. I can see the stars changing as I adjust focus, and I "rock" focus until I see pinpoint stars around the field. Takes about 30 seconds to tune focus. 

 

After focusing, if I've just finished a sequence, I'll pop into PHD2 and manually dither. That takes about 5 seconds for the dither to occur, and I'll also watch the stars real-time in SharpCap while the dither occurs. When the stars stop moving, I'll kick off another sequence. I am acquiring sequences 5-10 frames long with exposure lengths of 90-120 seconds. So I will dither only every 8-15 minutes. 

 

I combine dithering with CosmeticCorrection in PI, so there are actually no hot pixels left by the time I integrate. The dithering is more there to ensure that any remnant FPN that dark subtraction did not correct is eliminated, and to make sure that drizzling works (and when you have hundreds of frames, it works.) 



#42 Peter in Reno

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Posted 10 September 2016 - 12:59 PM

Newest SGP version released yesterday allows you to dither every N frames where N is the number of frames you enter.

 

Peter



#43 Jon Rista

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Posted 10 September 2016 - 12:59 PM

Hello Jon,

 

    Great post and your images are stunning, Thanks for giving such detailed information as I also have a 1600 and am also testing the QHY 183c. I live in severely light polluted skies only being 15 miles west of Manhattan and 3 miles north of Newark, NJ I have to get very creative with filters and hope to someday get what your getting out of your scope.  

 

By the way I'm using my 14" Meade native F8 and my RC 10" native F8, I also reduce these two scopes but have only been able to get down to about F5.2 

 

Thanks again for this post,

Joe

Your two scopes are much more capable than mine. The f-ratio is not all that important if you consider the total object signal being acquired. F-ratio is an indication of magnification and FoV, but it is actually not key to getting good SNR.

 

You have a 14" (355mm) and a 10" (245mm) scope. Both of those have considerably greater light gathering area than my 150mm refractor. Even accounting for the COs, both of those scopes are capable of acquiring significantly more light per unit time. Reduced to f/5.2, you should be able to acquire considerably more signal in the same amount of time. 

 

To be honest, with apertures that large, at f/5.2 you may find that you need 90-120 second subs at unity gain. Or, you might find that you are using 30 second subs (narrow band!) at gain 200. If you used longer exposures, I suspect the stars would clip too much. If you slap some narrow band filters on those rigs, you should be able to take advantage of higher gain imaging right away. 



#44 jlandy

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Posted 10 September 2016 - 01:18 PM

Newest SGP version released yesterday allows you to dither every N frames where N is the number of frames you enter.

 

Peter

it's like they read my mind... im excited to try this method out with fewer dithering steps



#45 Jon Rista

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Posted 10 September 2016 - 01:23 PM

 

Newest SGP version released yesterday allows you to dither every N frames where N is the number of frames you enter.

 

Peter

it's like they read my mind... im excited to try this method out with fewer dithering steps

 

Wow...seriously. Right on cue...we start using short NB exposures, they solve the dithering issue. Sweet!



#46 dkeller_nc

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Posted 10 September 2016 - 03:45 PM

OK, I'm convinced.  This is 12 minutes of integration with a 12nm Ha filter of NGC281.  Gain = 250, Brightness = 100, -15 deg C, 8 guided 90s exposures from red-zone LP.  Really amateurish processing in AutoStakkert and PS, no darks, flats or bias frames, and some seriously ugly bright stars (haven't quite figured out whether that's scope optics aberration, over exposure, lack of mount tuning, or all of the above).  But it does illustrate what's possible with very modest equipment investment by a complete newb to this game.

 

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  • NGC281.jpg


#47 ChrisWhite

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Posted 11 September 2016 - 06:59 AM

Jon,

 

SGP update really changes things.  I've been working towards how low of a gain I can push with fast scopes to avoid all the wasted time with dithering. Now with the ability to dither every "x" frames it opens up the options again.

 

When comparing subs from 76 gain 180 seconds to unity 90 second subs the latter looked much nicer with regards to noise.  The master bias from unity also looked much nicer, so this higher gain discussion is not trivial. 

 

I wonder if this high gain/short exposure imaging could be the new norm for LRGB as well.  I wonder if shooting 45 second exposures at gain 200 would trump 90 second exposures at unity.  With the lower read noise AND lower glow it would not take much for even VERY faint signals to rise above the noise floor.  I wonder if this is worth doing?



#48 telfish

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Posted 11 September 2016 - 07:08 AM

Chris 45 seconds at gain 200 in LRGB would swamp my system and saturate mose average stars. I would use maybe 10 seconds as a start. ultra short sumbs in LRGB is on my radar after success with 45 sec subs in narrow band at 360 gain.

 

My normal exposure in unity for LRGB is 45 seconds L 60 seconds RGB. F7.5 scope at 1200mm and even then my brightest stars are saturated!

 

I intended to use 200 for this so I will let you know how it goes


Edited by telfish, 11 September 2016 - 07:09 AM.


#49 ChrisWhite

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Posted 11 September 2016 - 07:25 AM

Chris 45 seconds at gain 200 in LRGB would swamp my system and saturate mose average stars. I would use maybe 10 seconds as a start. ultra short sumbs in LRGB is on my radar after success with 45 sec subs in narrow band at 360 gain.

 

My normal exposure in unity for LRGB is 45 seconds L 60 seconds RGB. F7.5 scope at 1200mm and even then my brightest stars are saturated!

 

I intended to use 200 for this so I will let you know how it goes

Are you using SGP?  I recently shot 180s subs at gain 76 (which would be 90s at unity) with f4.3 scope at 260mm and my histogram looked pretty tight to the left (RGB filters).  This is what I was basing my guess of 45 seconds at gain 200 which would be about 1 stop difference from Unity (2 stops from Gain 76.)  Were my subs way too long here:

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#50 ChrisWhite

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Posted 11 September 2016 - 07:41 AM

I "may" have answered my own question.  When I open one of these images in SGP and hover over the star cores, the ADU value appears totally maxed out... interpreted as over saturated.  :p

 

So with this camera, the histogram is basically useless.  It will be slammed up against that left wall with proper exposure I'm guessing..




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