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narrowband imaging in bortle class 9 skies with 1600mm pro

astrophotography beginner cassegrain Celestron dso eq Orion
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#1 Dentalpulp

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Posted 15 February 2020 - 03:30 AM

Hey all,

 

i just recently got into astrophotography, but i live in bortle class 9 skies, i am using celestron edgehd 8" with hyperstar to image, my issue is, even under 0 gain my ADU reaches 1100 under 30sec using narrowband filters and results in an image with tons of vignetting. i am not sure if i should be going for longer exposures anyway? my mount can handle up to 5mins of exposure but the images will be over exposed.

 

i've attached a single 30sec exposure of m42 in HA dark calibrated



#2 Dentalpulp

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Posted 15 February 2020 - 03:39 AM

https://drive.google...iew?usp=sharing

here is the image,

i am pretty sure that i am using the correct back focal distance 



#3 Varnius

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Posted 15 February 2020 - 05:04 AM

Do you take flats? That would help with vignetting.

Reaching 1000+ ADU with such fast optics as Hyperstar (f/2) even in narrowband sounds like something feasible. I guess it also depends on bandwidth of your filters. Not that I would worry about it - you can just take a bunch of shorter exposures to maintain ADU you need - obviously then you'll need a lot of storage and processing power to process all those images. 

 

Here are the exposure tables for ASI1600, no f/2 there, but you could extrapolate:

https://www.cloudyni...d-maybe-qhy163/



#4 Dentalpulp

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Posted 15 February 2020 - 07:18 AM

Ty, Varnius for swift reponse. it really helps to have some help because in my country its literally me and another guy that are into astrophotography! :S

 

but i want to confirm something, it is better to take longer subs as long as i dont overexpose,

1*so it is better to reduce gain and increase length of exposure?

,but i am living in 16.86 mag./arc sec2 bortle class 9 skies, and i have seen the chart at the link you provided, at 0 gain the narrowband image in 18mag/arch showed 9min exposure at f4,

2*i have no idea how that would translate to my 16.86 mag./arc f2 situation would gladly accept some help?,

3*and assuming all this is true for narrowband, does that mean broadband imaging is out of the question?

4*something else i did not understand is ADU above bias what does that mean exactly?

5*how much ADU my Bias have to be?

6*assuming what would happen if i went higher than recommended adu range for my camera?

 

please help me answering these 6 questions :D



#5 TareqPhoto

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Posted 15 February 2020 - 07:32 AM

Ok, first, which country are you live in?

 

Second, i live in light pollution sky too, it says Bortle 8/9 in the light pollution map of my country, with about 18 mag./arc sec2, so i don't think there is very big or huge difference between 18 and 16 anyway, people says with NB mainly Ha you can shoot even under full moon which means high brightness same or similar to LP.

 

I shoot with NB, but i do shoot with LRGB also, and for now because i am still testing and experimenting i don't care much about ADU or chart/table because that will lead me to frustration more than to success, at the end some people told me it is about getting results rather than being too scientific with numbers and equations, and when i do that i really started to have results even not great but they are good enough for me to keep going, if i was only caring about ADU then i won't have any results i am happy with and i will give up so quick long time ago, so just shoot and shoot and shoot, try different settings, don't force yourself with one settings, even if the results isn't good at least you get something and then you can improve from there, i heard all saying that LRGB or even OSC is like impossible under very bad light pollution, i agree, but i don't give up, and for NB i really do whatever i can and just get results, in fact what is funny is that i have some results that people said they dream about it to have it under dark skies while i did it with NB in my sky, not sure how much worse your sky over mine, but do NB first have time with it and then you can improve by the time.

 

If you can attach or post final result of whatever you image that will be good, not single exposure file only.



#6 Dentalpulp

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Posted 15 February 2020 - 02:27 PM

Hello Tareq,

 

I am from saudi arabia, and i guess you are right, i'll just try to get longer exposures and see if i end up with something better or not, but i really wanna use OSC camera when galaxy season is right around the corner.

 

here is the final image i got

https://drive.google...iew?usp=sharing

i've seen better, and i have alot of processing skills to learn but i was happy with the results for now and i stopped editing



#7 TareqPhoto

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Posted 15 February 2020 - 03:52 PM

Hello again,

 

Nice, so you are the neighbor, i live in UAE as you can see.

 

Longer exposures for most targets or nebulae will be the way to go, Orion is tricky, you need multiple exposures duration to have kind of HDR result, i am still working in that, and your result is really very nice, regardless it is not that true or real colors we see from others, but it is still nice, you can still process it different ways, or assigning each filter to a channel, try to change again and see, but yours isn't bad, maybe changing between Ha and OIII or between OIII and SII, play and see how it will go.



#8 Dentalpulp

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Posted 15 February 2020 - 04:14 PM

i will thank you tareq



#9 Ballyhoo

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Posted 15 February 2020 - 04:17 PM

If I lived in S.A, I think I would pretty often put my equipment in my car and drive to a really dark dark site. If you drove an hour out, would you not have like a bortle 4? What about 90 minutes away from home? I live in bortle 5.5. Tonight I am going to drive 30 minutes to a bortle 4 -- because it makes everything so much better. plus, it is so nice to view the really dark sky. But I can just imagine how dark it must be in the "Arabian nights," if you drove a little.


Edited by Ballyhoo, 15 February 2020 - 04:18 PM.


#10 TareqPhoto

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Posted 15 February 2020 - 04:32 PM

If I lived in S.A, I think I would pretty often put my equipment in my car and drive to a really dark dark site. If you drove an hour out, would you not have like a bortle 4? What about 90 minutes away from home? I live in bortle 5.5. Tonight I am going to drive 30 minutes to a bortle 4 -- because it makes everything so much better. plus, it is so nice to view the really dark sky. But I can just imagine how dark it must be in the "Arabian nights," if you drove a little.

Well, that really depends, i mean how wide is that light pollution spreading, i mean there are areas in desert where it is Bortle 1, and then another area where it is like Bortle 3 or 4, still amazing, but most likely it needs longer drive, in my country if i need to go to that very far desert where i can get into like Bortle 1-3 at least it means i have to drive minimum 3 hours one way, and there is another areas where it can be like Bortle 4-6, not a big desert, near mountains area, less time driving, but i feel like it is not that much clear anyway, let's say i can't see milky way or more stars, but definitely better than my area which is not completely bad by Zenith mainly after midnight.

 

I am now planning to get a small economic car, this will allow me to drive more, i have a 4Wheel drive that is very hungry, and the price of fuel in my country increased, and for someone like me without a job it is really too much, i mean don't compare it with Europe or USA, but it is more or higher than neighbors which is weird for me, and with that 4Wheel V8 [4.8L] this is too much, so that i don't drive even to half an hour distances, i really want to get into real dunes and dark skies, not necessary Bortle 1-2, but something like Bortle 3-4 will be fine for me, in fact from that light map pollution i see it mentioned that in my city for like about 10 minutes drive i can get into Bortle 6-7 rather than my 7-8, and for like 15-20min i may get into Bortle 5, but i really went there several times and i never see it any difference really, in fact from my yard is better because there is a fence and less lights around, while there although the street light is a bit far but it is an open space and i can see city lights at distance from all directions, and i don't see the stars being any clearer, but maybe with bino and camera it could be clearer.



#11 Swordfishy

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Posted 15 February 2020 - 08:41 PM

I live in a Bortle 9 zone AND I am shooting through 4 different very very bright LED lights almost shining down my tube.

Shooting narrowband I am exposing for 5 minutes at 200 gain 10 offset. F5.9

My subs actually tend to be on the dark side. Not sure what's going on there.

#12 Dentalpulp

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Posted 16 February 2020 - 04:43 AM

If I lived in S.A, I think I would pretty often put my equipment in my car and drive to a really dark dark site. If you drove an hour out, would you not have like a bortle 4? What about 90 minutes away from home? I live in bortle 5.5. Tonight I am going to drive 30 minutes to a bortle 4 -- because it makes everything so much better. plus, it is so nice to view the really dark sky. But I can just imagine how dark it must be in the "Arabian nights," if you drove a little.

well i still havent figured out how i would do it without direct electricity from my home, and how that would work, but yea bortle class 1 is like 2hours away. but i wonder what kind of dangers i might face in the desert being people or animal wise. and since i am still figuring stuff out from my roof top is quite easier to make mistakes rather than spending 4 hours on a road trip that would end in failure =(



#13 Dentalpulp

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Posted 16 February 2020 - 04:45 AM

I live in a Bortle 9 zone AND I am shooting through 4 different very very bright LED lights almost shining down my tube.

Shooting narrowband I am exposing for 5 minutes at 200 gain 10 offset. F5.9

My subs actually tend to be on the dark side. Not sure what's going on there.

i noticed that most of my subs also look dark but i thought that might be due to short exposures (30sec) at f2, but i noticed once i stacked my images and used dynamic background extraction in pixinsight it dramaticly showed me more details.


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#14 Swordfishy

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Posted 17 February 2020 - 03:01 PM

i noticed that most of my subs also look dark but i thought that might be due to short exposures (30sec) at f2, but i noticed once i stacked my images and used dynamic background extraction in pixinsight it dramaticly showed me more details.

Yeah if you are shooting at F2, you will DEFINITELY need to keep your subs short. I have a Rokinon 135MM F2 and even at F2.8 it overexposes really quickly. For example, for Orion, the most I can do is 10 seconds at 400 iso, and even then the sub is very bright.



#15 bobzeq25

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Posted 17 February 2020 - 04:04 PM

That's an average value of 400ADU (16 bit), calibrated (dark subtracted.  Without knowing the camera or gain this is approximate, but I'd guess 60 seconds would be better.  In Bortle 7, with a C8 RASA at F2, ASI183 camera, I do 120 seconds narrowband at gain 100.

 

I could tell better with the camera info.  EDIT: I missed the camera in the title, still need the gain.

 

Or you could.

 

Look at the average value of that dark subtracted light in Image-Statistics.  Using the camera data, convert that into electrons. 

 

Take the camera data, find the read noise in electrons.  Square the read noise.   Compare it to the average above.  You'd like the average to be somewhere in between 5 and 10 times the read noise squared.  That balances out too much read noise (too many short subs) and too little dynamic range (too few long ones).

 

Lowering gain to lengthen exposure can be a good idea.  It depends on the read noise of your camera.

 

Broadband is hard in your skies, even with HyperStar (which helps)..  It will work significantly better with a mono camera and LRGB filters and processing.  With HyperStar you'd need a filter slide, and some effort.

 

Part of your image (the bright stars) will always exceed the top ADU for you camera.  At that point, the stars get large, and, with one shot color, you lose all the color information. 


Edited by bobzeq25, 17 February 2020 - 04:28 PM.

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#16 TareqPhoto

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Posted 17 February 2020 - 04:12 PM

This is with 300sec [5min] exposures, at gain 200, under my Bortle sky, Bortle sky 8/9, Ha filter, and the lens is at F2.8

Attached Thumbnails

  • Heart Nebula.jpg


#17 Dentalpulp

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Posted 26 February 2020 - 01:14 PM

That's an average value of 400ADU (16 bit), calibrated (dark subtracted.  Without knowing the camera or gain this is approximate, but I'd guess 60 seconds would be better.  In Bortle 7, with a C8 RASA at F2, ASI183 camera, I do 120 seconds narrowband at gain 100.

 

I could tell better with the camera info.  EDIT: I missed the camera in the title, still need the gain.

 

Or you could.

 

Look at the average value of that dark subtracted light in Image-Statistics.  Using the camera data, convert that into electrons. 

 

Take the camera data, find the read noise in electrons.  Square the read noise.   Compare it to the average above.  You'd like the average to be somewhere in between 5 and 10 times the read noise squared.  That balances out too much read noise (too many short subs) and too little dynamic range (too few long ones).

 

Lowering gain to lengthen exposure can be a good idea.  It depends on the read noise of your camera.

 

Broadband is hard in your skies, even with HyperStar (which helps)..  It will work significantly better with a mono camera and LRGB filters and processing.  With HyperStar you'd need a filter slide, and some effort.

 

Part of your image (the bright stars) will always exceed the top ADU for you camera.  At that point, the stars get large, and, with one shot color, you lose all the color information. 

thanks for the response

i could not understand this part very well, "dark subtracted light in Image-Statistics", "Square the read noise", "Compare it to the average above"

i used asi 1600mm pro at gain 0 offset 10

i am sorry i got busy with life couldn't check in earlier 



#18 Dentalpulp

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Posted 26 February 2020 - 01:15 PM

This is with 300sec [5min] exposures, at gain 200, under my Bortle sky, Bortle sky 8/9, Ha filter, and the lens is at F2.8

amazing image taric, this is after calibration? or single frame?



#19 Peregrinatum

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Posted 26 February 2020 - 01:22 PM

Unfortunately with that much LP faster FR only hurts you.



#20 TareqPhoto

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Posted 26 February 2020 - 06:05 PM

amazing image taric, this is after calibration? or single frame?

Thanks.

 

After calibration

 

Tareq




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