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longer exposures are way better even for EAA

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#1 DSO_Viewer

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Posted 09 November 2019 - 12:52 PM

I just watched an excellent video by Dylan O'Donnell clearly showing us the huge benefits for longer exposures. He was using a mono 1600 camera and a fast 8" Hyperstar scope (yes Hyperstar). He took 10 x 30 secs, 5 x 60 secs and 1 x 300 secs all totaling 5 minutes. You can clearly see the random noise as your sub-exposures lower and the details are no where near the amount that can be observed. Here is the link for those interested in this very interesting test and a screen shot of Dylan's test results.

 

https://www.youtube....eature=youtu.be

 

Steve

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#2 Jeff Lee

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Posted 09 November 2019 - 12:59 PM

Ummm, I like to see stuff not wait for it to develop. So for me a 8-15 seconds maybe 4 or 5 stacks and I am off to the next object. Yes long exposure develops more detail but EAA is about real time (or near to it viewing). This is not news in the EAA group.


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#3 DSO_Viewer

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Posted 09 November 2019 - 01:12 PM

Ummm, I like to see stuff not wait for it to develop. So for me a 8-15 seconds maybe 4 or 5 stacks and I am off to the next object. Yes long exposure develops more detail but EAA is about real time (or near to it viewing). This is not news in the EAA group.

" This is not news in the EAA group" I did not present this as news but actual fact. There are some of us willing to wait a bit longer for cleaner highly detail to observe. 8-15 secs is not real time and I believe that part of EAA is watching the object develop over time. Again I did not post this to say that 5 sec subs are not EAA but just voicing my own opinion.

 

Steve


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#4 homerdt

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Posted 09 November 2019 - 01:17 PM

" This is not news in the EAA group" I did not present this as news but actual fact. There are some of us willing to wait a bit longer for cleaner highly detail to observe. 8-15 secs is not real time and I believe that part of EAA is watching the object develop over time. Again I did not post this to say that 5 sec subs are not EAA but just voicing my own opinion.

 

Steve

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#5 CharlesC

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Posted 09 November 2019 - 01:27 PM

Most folks would have a hard time doing a 300 second single exposure with their sensitive EAA camera.  Only the darkest location would allow that.  Most suburbs I've lived would only let me take 1-2 second exposures due to sky glow of city lights.  

Those don't show much without stacking for several minutes.


Edited by CharlesC, 09 November 2019 - 01:27 PM.


#6 DSO_Viewer

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Posted 09 November 2019 - 02:02 PM

Most folks would have a hard time doing a 300 second single exposure with their sensitive EAA camera.  Only the darkest location would allow that.  Most suburbs I've lived would only let me take 1-2 second exposures due to sky glow of city lights.  

Those don't show much without stacking for several minutes.

I did not mean that we have to go 300 sec for EAAlol.gif. That would not be practical but it would not hurt and would benefit to go 30 to 60 seconds and stack for a trade off between the two. I read so much here that EAA is only for those who go 2 to 8 seconds and beyond that is not EAA. I think this is sad and going a little bit longer would only improve the observing while still allowing for multiple objects to be viewed during your session. Again just my opinion and what I have noticed over the last few years of trying out different approaches. I just though this video from Dylan would be of some benefit.

 

Steve 


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#7 DSO_Viewer

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Posted 09 November 2019 - 02:04 PM

I did not mean that we have to go 300 sec for EAAlol.gif. That would not be practical but it would not hurt and would benefit to go 30 to 60 seconds and stack for a trade off between the two. I read so much here that EAA is only for those who go 2 to 8 seconds and beyond that is not EAA. I think this is sad and going a little bit longer would only improve the observing while still allowing for multiple objects to be viewed during your session. Again just my opinion and what I have noticed over the last few years of trying out different approaches. I just though this video from Dylan would be of some benefit.

 

Steve 

Charles what is a sensitive EAA camera? I thought most cameras used these days were used in both the EAA & AP forums.

 

Steve


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#8 barbarosa

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Posted 09 November 2019 - 02:13 PM

Charles it has been years since I was in Atlanta but I expect the area isn't orders of magnitude worse than the the San Francisco-Oakland- San Jose exurbia, the red zone, no Milky Way and no several other objects that we used to see. Though if  you are in the center of the white it might be the critical difference.

 

But so far I find it is possible to do EAA with longer exposures than 2s. My LN-300 has gone where the woodbine twineth, replaced by ZWO CMOS cameras.

 

For a long time I've used exposures of 15 or 30s and gains in the 300-350 range, but many objects do well with exposures of >60s and gain adjusted as needed. Two of the best broadcasters on Night Skies Network (.com) routinely use exposures of 60s, one is in the Atlanta area and the other is not I think in a rural site.

 

I use 85 and 120 mm refractors at f/6 and f/7 primarily and for the small and dim a C-9.25 at f/10 or 20.

 

My LN-300 has gone where the woodbine twineth, and now it is ZWO CMOS cameras, such as the 120 mono, 290, 224 and 294 Pro. 

 

I do use filters but for DSOs a mild sky glow filter and sometimes an IR block filter, for the moon sometimes an infrared pass filter. 

 

As a rule I do not save and post process images, so issues of exposure length aside, I think EAA is what I do. As for those who go out to 180s for narrow band say, well If they and we want to watch the paint dry, its just a choice, neither better or worse than others.



#9 GaryShaw

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Posted 09 November 2019 - 03:48 PM

I just watched an excellent video by Dylan O'Donnell clearly showing us the huge benefits for longer exposures. He was using a mono 1600 camera and a fast 8" Hyperstar scope (yes Hyperstar). He took 10 x 30 secs, 5 x 60 secs and 1 x 300 secs all totaling 5 minutes. You can clearly see the random noise as your sub-exposures lower and the details are no where near the amount that can be observed. Here is the link for those interested in this very interesting test and a screen shot of Dylan's test results.

 

https://www.youtube....eature=youtu.be

 

Steve

I'm just a year into EAA now Steve and I appreciate the helpful comparison and the Youtube link. Folks like me, still very much on the learning curve, benefit a lot from the experiences, biases and opinions of others - humor is good too! My humble gear and AZ mount let me go to 20-30 seconds - except when looking to the Zenith.....learned that pretty well the last few nights chasing some new friends way up there.

 

We might want to all recall Robin Glover's March 2019 AP group presentation (available on youtube) on why 2-3 seconds was the optimal sub exposure....in his opinion of course.

Cheers

Gary



#10 CharlesC

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Posted 09 November 2019 - 04:04 PM

Charles it has been years since I was in Atlanta but I expect the area isn't orders of magnitude worse than the the San Francisco-Oakland- San Jose exurbia, the red zone, no Milky Way and no several other objects that we used to see. Though if  you are in the center of the white it might be the critical difference.

 

But so far I find it is possible to do EAA with longer exposures than 2s. My LN-300 has gone where the woodbine twineth, replaced by ZWO CMOS cameras.

 

For a long time I've used exposures of 15 or 30s and gains in the 300-350 range, but many objects do well with exposures of >60s and gain adjusted as needed. Two of the best broadcasters on Night Skies Network (.com) routinely use exposures of 60s, one is in the Atlanta area and the other is not I think in a rural site.

 

I use 85 and 120 mm refractors at f/6 and f/7 primarily and for the small and dim a C-9.25 at f/10 or 20.

 

My LN-300 has gone where the woodbine twineth, and now it is ZWO CMOS cameras, such as the 120 mono, 290, 224 and 294 Pro. 

 

I do use filters but for DSOs a mild sky glow filter and sometimes an IR block filter, for the moon sometimes an infrared pass filter. 

 

As a rule I do not save and post process images, so issues of exposure length aside, I think EAA is what I do. As for those who go out to 180s for narrow band say, well If they and we want to watch the paint dry, its just a choice, neither better or worse than others.

Someday I will upgrade, but I've been in apartments with little opportunity for EAA for a while so pointless to upgrade now. 



#11 barbarosa

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Posted 09 November 2019 - 06:55 PM

 

We might want to all recall Robin Glover's March 2019 AP group presentation (available on youtube) on why 2-3 seconds was the optimal sub exposure....in his opinion of course.

Cheers

Gary

I certainly won't be the one to step up and suggest the Robin is wrong, but I believe that was not exactly what he advocates.  He said that while it is possible to take 1 second exposures, 1s would be an extreme case.  His general rule is shorter in in light polluted areas and longer under areas of less light pollution.

 

He points to his "brain" tool in SharpCap as a way to find the optimal exposure for a given camera under a given sky. I been giving the brain some attention and for example with the 224  and targets in different areas of the sky.  You have options to set some parameters, such as unity gain or maximum dynamic range and the brain may suggest very different settings. On M27 for example, Gain=132 Exposure=22.64095 and Gain=61 Exposure=43.541859. 

 

Without the brain I might have picked 8s and gain 350 or some such.


Edited by barbarosa, 09 November 2019 - 06:56 PM.

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#12 barbarosa

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Posted 09 November 2019 - 07:16 PM

Charles, I get that about apartments. Looking back that camera and those like it were an astonishing revelation to me. I had a couple of LN-300s. One went off to Florida and he who we do not discuss kept it and sent me an amusing email that I think CN wouldn't like me to quote even at this late date. The other stayed in use for quite a while. I don't know where it lurks but little reminders keep turning up, 5mm adapter rings and the like. There are guys saying that it is still a very good cam for lunar and planetary.


Edited by barbarosa, 10 November 2019 - 03:50 PM.


#13 CharlesC

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Posted 09 November 2019 - 07:36 PM

Charles, I get that about apartments. Looking back that camera and those like were an astonishing revelation to me. I had a couple of LN-300s. One went off to Florida and he who we do not discuss kept it and sent me an amusing email that I think CN wouldn't like me to quote even at this late date. The other stayed in use for quite a while. I don't know where it lurks but little reminders keep turning up, 5mm adapter rings and the like. There are guys saying that it is still a very good cam for lunar and planetary.

I am trying to get more active again.  If I manage to make trip to dark site I may make folks suffer through a few LN300 pics.  :-)  

Karma restores balance to the universe.  Time marches on.


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#14 Rickster

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Posted 10 November 2019 - 10:43 AM

After I got autoguiding, I ran similar experiments numerous times.  I found that for my location, the optimum exposure length varied from night to night.  On one night, a single long exposure would be strikingly better, but more often than not, a single long exposure would be inferior.  It depended on how steady the conditions were.  Long exposures can be wrecked by a long list of disturbances;  unsteady atmospheric conditions, occasional wind gusts at ground level, clouds/high level haze that come in and out, jet planes, satellites, someone driving by, pets,,,,you get the idea.  My general rule is to use the longest exposures that conditions will permit.  This can range from 2 seconds to 5 minutes.

 

It also depends on the camera and the focal length. 

 

My starting point is usually 10 seconds for the 183 or 290, and 30 seconds for the DSLRs. 

 

The DSLRs benefit from longer exposures.  So, in their case, I tend to run longer exposures and use Astrotoaster to select the best exposures for stacking.  AT gives each exposure a score.  You tell it what best percentage you want to keep.  On a good night I might set it to keep 90% of the exposures.  On a not so good night, I might set it to 40%.  AT also lists individual exposures so that I can click through them while it is stacking and delete bad exposures on the fly.  Then I can restack at the end.  This is a good way of getting rid of satellite traces, etc. 

 

Sharpcap can also be used to screen out bad exposures, using the filters, but not quite as well as Astrotoaster, in my experience.  When using Sharpcap, I usually get the best results by shortening exposures.

 

I have dark skies, so I don't have to worry about long exposures saturating pixels with sky glow.  But, as pointed out above, some people do.

 

Anyway.  That is what works for me.  Your situation may be different.


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#15 Jeff Lee

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Posted 10 November 2019 - 11:15 AM

My point was/is that 5 minute exposures are often not possible where folks do EAA. When the rules were updated for this forum the discussions were quite "heated" when discussing exposure times and any post processing. I would venture to say that most folks who have gone to EAA live in places where 90% of their EAA goes white (without filters) in 30 seconds. Yes, filters do help but Robin of SC seems to know what this EAA stuff is all about, greatly surpassing anything I care to delve into. I guess I felt this post what really addressing AP when it hits 300 seconds as the recommend exposure. And yes I have let my SLT/80/224 run for half an hour at a dark site, but at home with my C8/Es102 using my ZWO294 MC 10-15 seconds works for me (and it may not work for you) because of my sky conditions.


Edited by Jeff Lee, 10 November 2019 - 11:30 AM.

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#16 DSO_Viewer

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Posted 10 November 2019 - 12:44 PM

I'm just a year into EAA now Steve and I appreciate the helpful comparison and the Youtube link. Folks like me, still very much on the learning curve, benefit a lot from the experiences, biases and opinions of others - humor is good too! My humble gear and AZ mount let me go to 20-30 seconds - except when looking to the Zenith.....learned that pretty well the last few nights chasing some new friends way up there.

 

We might want to all recall Robin Glover's March 2019 AP group presentation (available on youtube) on why 2-3 seconds was the optimal sub exposure....in his opinion of course.

Cheers

Gary

Thank you Gary for your feedback. What I see in the video example is at 30 sec subs the brightest nebulous appears and no matter how many are stacked you will never see the fainter stuff. It seems as you go longer (within EAA reason) each individual subs contains more of the object and stacking only removes the noise allowing for clearer signal. I much as I respect Robin of Sharpcap, I cannot see 2-3 seconds collect enough signal to over come the noise.

 

Steve 



#17 mikenoname

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Posted 10 November 2019 - 01:23 PM

After I got autoguiding, I ran similar experiments numerous times.  I found that for my location, the optimum exposure length varied from night to night.  On one night, a single long exposure would be strikingly better, but more often than not, a single long exposure would be inferior.  It depended on how steady the conditions were.  Long exposures can be wrecked by a long list of disturbances;  unsteady atmospheric conditions, occasional wind gusts at ground level, clouds/high level haze that come in and out, jet planes, satellites, someone driving by, pets,,,,you get the idea.  My general rule is to use the longest exposures that conditions will permit.  This can range from 2 seconds to 5 minutes.

 

I agree, Rick. I think Dylan's video and the premise of this thread is attempting to apply a broad, sweeping generalization to a pretty dynamic situation.

 

Aside from the variables you mentioned, there is also the target itself. For example, I have feeling that a target with a much greater surface brightness might respond very differently to this test.


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#18 alphatripleplus

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Posted 10 November 2019 - 10:44 PM

If you read the comments after the video, Dylan indicates that his series of shots were taken through a narrowband filter in Hydrogen alpha with a mono 1600 camera - he did his tests around full moon. As the background sky brightness (and associated noise) is greatly suppressed in H-alpha (compared to shooting with no fliter), subs must be much longer to reach the point where sky background noise dominates read noise as the major component of total noise. Without a narrowband filter, sky background noise (for a low read noise CMOS camera) can dominate in a few tens of seconds or less.. However, if you take the same sensor and shoot through a H-alpha filter sky background noise is vastly suppressed, read noise is unchanged, and so it takes much longer subs for sky background noise to dominate read noise.

 

Basically, his results aren't surprising if you are doing H-alpha. If he had done his tests shooting unfiltered, the optimal sub lengths would be much shorter, particularly if you are dealing with a lot of LP. 


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#19 Astrojedi

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Posted 14 November 2019 - 04:55 PM

The only benefit of longer subexposures is to overcome read noise. Higher the QE, higher the gain used and the lower the read noise of the sensor, less is the SNR impact of longer sub exposures.

A few caveats to Dylan’s analysis :
1. The 1600 is not a high QE cameras like the newer Sony CMOS sensors which makes it less suitable to shorter subexposures
2. You need to use high gain for shorter sub exposures - one to overcome read noise and the other to minimize quantization error / signal loss to quantization

Another way to say this... as long as you have a sensor with meaningful read noise, longer sub exposures will improve SNR but depending on the QE, read noise and gain you will hit diminishing returns with longer sub exposures pretty quickly.

Also keep in mind in EAA we are not trying to optimize SNR and dynamic range like pretty picture imaging. Dylan’s discussion is more focused on imaging.
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#20 Noah4x4

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Posted 14 November 2019 - 06:08 PM

I have been waiting over three months to try this same experiment. UK weather in my location has been abysmal.

 

I gave up wedge/polar alignment after a year of frustration battling the infamous Starsense on wedge bug. By the time it was fixed, I had bought Hyperstar, had abandoned my wedge and been lured into the simplicity of EAA and short stacked exposures. I then had an enjoyable 12 months until this Autumn (Fall)  after which continuous cloud has been routine.

 

Normally, my EAA routine is to use multiple (between) 5 second to 20 second stacks and frankly, I have not noticed much performance difference between these times on Hyperstar as my Atik Horizon camera already has extremely low read noise. My understanding is that stacking increases SNR. Also that stacking multiple exposures at the OPTIMAL exposure time is better than a single exposure. The doubt in my mind is whether the OPTIMAL exposure time exceeds 20 seconds on Hyperstar (e.g. my limit on an Alt-Az without wedge). 

 

I have since reassembled my wedge, lured by my curiosity. Will fewer stacks, but longer exposures tease out more detail? The obvious answer (theoretically) must be yes as that is the premise of long exposure AP. However, Hyperstar is between 13x and 33x faster (depends on scope). On mine, the ratio is circa 25x. Hence a 10 second exposure is already equivalent to over 4 minutes. Hence, what is the OPTIMAL exposure time x multiple stacks on Hyperstar?

 

I might have the answer in about January, weather permitting. I have a suspicion that my wedge might as well be returned to its box when using Hyperstar and 20 seconds x multiple stacks is plenty for observing.


Edited by Noah4x4, 14 November 2019 - 06:19 PM.


#21 geminijk

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Posted 14 November 2019 - 09:56 PM

Defeats the purpose, dare I say the MAIN purpose of EAA, which is OBSERVING.  I mean c'mon, we all know longer exposure is better, but we do the SHORTEST possible to observe the object, not go after the best picture. 

 

John


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#22 NaNuu

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Posted 15 November 2019 - 08:24 AM

Defeats the purpose, dare I say the MAIN purpose of EAA, which is OBSERVING.  I mean c'mon, we all know longer exposure is better, but we do the SHORTEST possible to observe the object, not go after the best picture. 

 

John

I disagree somewhat. (-: To me, the quality of my observation is related to the quality of the picture. But I agree in that EAA doesn't mean to produce the best possible picture regardless of how much time it would take...

 

Anyway, I understand Steve's topic that for a given amount of observation time, it might be better to use few long exposure frames instead of many short exposure frames - so it's not the question of doing the shortest possible - it's how we should best split that shortest possible time into exposure times of the frames we take and stack. Btw: I guess the correct answer is "it depends"... That's the reason I like the brain tool of SharpCap.


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#23 GaryShaw

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Posted 15 November 2019 - 09:15 AM

Defeats the purpose, dare I say the MAIN purpose of EAA, which is OBSERVING.  I mean c'mon, we all know longer exposure is better, but we do the SHORTEST possible to observe the object, not go after the best picture. 

 

John

Hi

I was compelled to get into EAA because I wanted to see and learn about what’s out there not because I wanted to revisit and update my engineering education and learn about today’s  nucs, WiFi, active usb3 cable science, etc. I’m in Boston for 2/3 of the year and that means I see nearly nothing with visual eyepiece observing. EAA has opened up the universe to me, at least enough of it that I’ll never run out of enticing objects to track down and learn about. Now I need to get better at it.

Yet, now that I’m observing onscreen, I find myself constantly tempted to record an image of what I see to share these with friends, family etc. If I don’t catch myself, I can slip into obsessing over the image in lieu of using the image to study the object. Of course, an optimal onscreen image helps a lot in studying the subtlety of object structure as seen in a nebula or Galaxy. So, in key ways, getting a decent image with broad dynamic content serves both goals of object study and image capture. A little added time spent bringing out the detail is worth it.

 

To keep me focused on learning more about the universe and how it’s structures have come to be, I include in my observing plans a few aspects of each object that I hope to observe and how these depict or demonstrate what we know about in terms of the evolution of the universe. For example many of us teased out the relativistic jet of M87 earlier in the year when so much was in the news and being discussed about the ‘black hole’ image produced by the Event Horizon Team. After seeing that ‘live’ onscreen, for the past 9 months I’ve read whatever current information is available on black hole formation, dynamics and eventual evaporation. Sometimes I look at the image I grabbed of M87 and the jet while I’m reading...a good image can energize and augment the learning process. I’m hoping to get skilled enough at acquiring good live images that it becomes nearly automatic, like ‘muscle memory’, to enable the observing process rather than becoming the ‘goal’ of that process. 

 

I learn so much about the imaging skills I need to acquire from discussions like this one and from all of you that know so much more than I. I also believe that, if we’re observers, more than we are Astrophotographers, the spirit of John’s point above is worth bearing in mind: that the imaging aspect is in support of the observation and learning process - not the other way around. 
Gary

 

[ ps: I have to add how awed I am by the incredible AP images we see here in CN. Having such images onscreen to use to tweet/explore and learn about object structure ‘live’ would be awesome...if only I had the time, talent, equipment and patience. ]


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#24 Astrojedi

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Posted 15 November 2019 - 01:58 PM

I know there are strong opinions on this but to me long vs. short exposure boils down to personal preference.

 

For me, I very much enjoy short exposures for EAA. Yes, I could optimize the SNR by exposing longer (which I do when I am doing traditional imaging) but to me it feels less live.

 

It is hard to describe... it is the same reason that Night Vision to me feels even closer to visual observing even though the technology and principle is pretty much the same as imaging. It is the immediacy of the experience.

 

Finally, I do most of my EAA with the ASI290MM mono camera, The camera has 80%+ QE and at a gain of 350 has just 1e read noise! At such low levels of read noise you hit diminishing returns on SNR very quickly with longer exposures. While I typically use 4s sub exposures, I have found that I rarely need sub exposures longer than 8-10s even for very faint objects and even with H-Alpha filters.

 

But if you are ok with longer sub exposures then you should enjoy EAA that way. And for some cameras and setups you need longer exposures.


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#25 DSO_Viewer

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Posted 18 November 2019 - 12:03 PM

Thank you to everyone that got into the discussion here and added their thoughts. In my conclusion it seems that for EAA to get the most detail out of the image within reasonable wait time is up to 30 seconds. This mainly goes to the users here with focal ratios on average between f4 to f6, moderate light pollution requiring filtration and a mount that can track decently for the duration. I know that we are all striving for real-time results but the present technology is not available as of yet unless you have a lot of money to buy a very high-end camera.

 

Steve




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