Hi guys. Recently I upgraded my remote rig with an ASI 2600MM Duo, mounted on a reduced FRA400 (280mm@f3.9). I found the sweet spot for broadband targets with 300-360s exposures at gain 100, but I can't find the right exposure time for NB (Antlia EDGE 4.5nm Ha). Looking at the histogram in NINA, I would assume an exposure of 1200-1800s, and even the dedicated plugin suggests something similar (1600s). However, I am doubtful, as a search here on AB shows that no one with this camera shoots for so long, not even with much slower focal ratios. The average is around 300s, with some exceptions at 600s. So I wonder if with this camera it is not crucial to overcome the readout noise, or if it is appropriate to modify the gain to have shorter exposure times. The setup is installed in Manciano under a sky with an average SQM of 21. Thanks in advance to anyone who wants to share some info with me.
ASI 2600 MM - recommended gain and exposure time for NB
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Not exactly apples to apples, but I have a Poseidon-M which has the same sensor (minus the duo part). I also have Antlia 3nm filters that I use with a reduced FRA600 shooting 420mm @F3.92. My skies are not quite as dark being about a bortle 4.5 or roughly 20.5 sqm. For my setup, I always use 0 gain for broadband and HCG for Narrowband. I do this to get the most dynamic range possible. Exposures times vary based on the target, but are usually 180 seconds for broadband and 600 seconds for Narrowband. Maybe this can help, but take it with a grain of salt as every setup is a little different.
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Unless it's an extremely bright target, my go to with a 571 sensor has been 20 minutes for narrowband with HCG. Bortle won't matter as much for narrowband, but for what it's worth, I'm around 20.7 on average for SQMs. Theres really no limit to your exposures with narrowband though. I've even shot 40 minute, but the actual gain feels alot less dramatic, plus you still need to plan out enough subs for rejection purposes.
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I shot regularly at gain 200 with NB with good results on my 2600mm. There are exceptions, but I find most targets don't require higher dynamic range.
Imo, but maybe some will disagree or can correct me if I've been wrong all along: it doesn't matter. As I see it, at 100 gain you get almost no loss in dynamic range but definitive drop in read noise, so "Set it and never change it" is my go-to. I personally think the exposure time depends: I like to just keep it at 300/600s for broad/narrowband, regardless of my telescopes (f6.3, f10) but for casual RGB shots of stars to just add into a primarily narrowband image started playing with shorter 120s now.
For me personally it comes down to mostly general conditions, rather than "the perfect technical exposure time". Imaging in a windy area and are prone to gusts, losing entire 10 minute subs will hurt more and be more likely than when just doing 5 minutes instead, so maybe taking a step down isn't a bad idea. OTOH, stacking and data storage is a breeze if you have only half the frames. I would totally do half an hour exposures in narrowband if I knew for certain that clouds, wind and guiding are always gonna play along perfectly ;)
For me personally it comes down to mostly general conditions, rather than "the perfect technical exposure time". Imaging in a windy area and are prone to gusts, losing entire 10 minute subs will hurt more and be more likely than when just doing 5 minutes instead, so maybe taking a step down isn't a bad idea. OTOH, stacking and data storage is a breeze if you have only half the frames. I would totally do half an hour exposures in narrowband if I knew for certain that clouds, wind and guiding are always gonna play along perfectly ;)
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Right exposure time should be calculated, but I think that 600-1200s would be okey with your specs. 300s is example too short for you to swamp read noise. It's totally different in cities but your sky is dark as mine so exposure time would be more important if you want to keep read noise level low.
I have also FRA400/F3.9 and this with Antlia 3nm narrowbands and ASI294MM camera (sky 21-21.5). I use 900s (15 min) exposures and that is prefect for me.
I have also FRA400/F3.9 and this with Antlia 3nm narrowbands and ASI294MM camera (sky 21-21.5). I use 900s (15 min) exposures and that is prefect for me.
I image with a 2600MM in skies of 21.4 using a 130mm refractor at f5.7. For narrowband settings I use gain 100 and offset 30 with an exposure time of 600secs. I tried a gain of 0 and that failed badly. I also tried 400secs exposure time and that is OK but 600secs seems to be a sweet spot.
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Yikes, such long subs. at a gain of 100 on a 2600 it only takes 24 sec. to swamp read noise by a factor of 12. At zero gain about 3 min. will do it. Unless you are under very dark skies, shot noise will totally overwhelm the read noise of a 2600.
I use the 2600MM under Bortle 4 skies here
300s for everything (RGB and NB) unless it's a bright target like orion for example!! I also run at gain 100 and I've had no troubles at all with these settings on either my Evolux 62ED or Quattro 250P
For thar only images I stick to 20s max exposure time purely for camera linearity purposes so it doesn't over saturate the stars
300s for everything (RGB and NB) unless it's a bright target like orion for example!! I also run at gain 100 and I've had no troubles at all with these settings on either my Evolux 62ED or Quattro 250P
For thar only images I stick to 20s max exposure time purely for camera linearity purposes so it doesn't over saturate the stars
I use the 2600MM with a 130mm refractor at f/5.0 and SQM 21.9 … unity gain (100) and 300 sec for narrowband (6.5 um) filters. I'll occasionally go to 600 sec but 300 works quite well
I’m sure no expert but I generally am 300sec at gain 100 for RGB and 600sec at gain 300 on an f7 or f10 scope. Good question to ask as I am always confused about this one.
I’m sure no expert but I generally am 300sec at gain 100 for RGB and 600sec at gain 300 on an f7 or f10 scope. Good question to ask as I am always confused about this one.
I wouldn't increase the gain or the exposure length for the slower scopes as 100 is really the sweet spot for this camera. You're going to gather the same number of photons per unit of time, you shouldn't ever have to go longer than 180 sec. and that's under B1 skies.
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Tony Gondola:I’m sure no expert but I generally am 300sec at gain 100 for RGB and 600sec at gain 300 on an f7 or f10 scope. Good question to ask as I am always confused about this one.
I wouldn't increase the gain or the exposure length for the slower scopes as 100 is really the sweet spot for this camera. You're going to gather the same number of photons per unit of time, you shouldn't ever have to go longer than 180 sec. and that's under B1 skies.
You saying for 180 seconds and Gain 100 for RGB and NB too?
Tony Gondola:I’m sure no expert but I generally am 300sec at gain 100 for RGB and 600sec at gain 300 on an f7 or f10 scope. Good question to ask as I am always confused about this one.
I wouldn't increase the gain or the exposure length for the slower scopes as 100 is really the sweet spot for this camera. You're going to gather the same number of photons per unit of time, you shouldn't ever have to go longer than 180 sec. and that's under B1 skies.
You saying for 180 seconds and Gain 100 for RGB and NB too?
You could go longer for NB because shot noise is less but there's no reason to.
Interesting. I will have to try it.
Interesting. I will have to try it.
You might be surprised. Don't compare subs, compare the final stack.
Can't speak for that camera as in the past I used a QSI 683 monochrome with a C14 at F10 and shooting the Horsehead in Ha 3nm and used 1200 to 1800 second subs
with great results so I think it depends on the target . I don't think it will really matter so much using your Ha filter with longer exposures.
with great results so I think it depends on the target . I don't think it will really matter so much using your Ha filter with longer exposures.
I do 420 seconds with my ASI533MM and ASI2600MM with my 3nm Antlia SHO filters. For RGB (I don't do L), it depends on target and the sky and varies between 180s and 300s. With some really faint narrowband targets like OU4, I have even done 1200s for OIII.
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I have the ASI2600MM and use Chroma 36mm filters. I operate at 160 gain and vary my exposure time between 300s and 600s. I determined that a gain of 150 is enough to lift the histogram in NINA off the left edge, and I added 10 to give a little buffer.
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What's the benefit of keeping the subs short if you have the headroom on the camera? Seems an odd way to use your camera.
I typically use 300 sec subs with NB, sometimes 600 sec, at 100Gain. With limited clear skies (and not the best viewing - trees obscure everything lower than 25 degrees) using 600 sec doesn't get me enough subs in an evening.
Himanshu Pandey:
What's the benefit of keeping the subs short if you have the headroom on the camera? Seems an odd way to use your camera.
If that question was directed at me, I'll tell you what my thinking is. By shooting short subs you have more of an opportunity to improve your data. If you do say, 600 sec. subs, unless you are willing to to throw it away, you are stuck with whatever degradation happens during those 300 sec. Conditions and hardware aren't perfect, we all know what those things can be. By shooting shorter subs you have an opportunity to get rid of the problem with loosing a lot of integration.
Tony Gondola:Himanshu Pandey:
What's the benefit of keeping the subs short if you have the headroom on the camera? Seems an odd way to use your camera.
If that question was directed at me, I'll tell you what my thinking is. By shooting short subs you have more of an opportunity to improve your data. If you do say, 600 sec. subs, unless you are willing to to throw it away, you are stuck with whatever degradation happens during those 300 sec. Conditions and hardware aren't perfect, we all know what those things can be. By shooting shorter subs you have an opportunity to get rid of the problem with loosing a lot of integration.
I agree with your thinking but the downside of short subs on the larger sensor cameras is the data processing and storage issue. Each frame is 50mb for a 2600 and it adds up.
Since moving to AZEQ-6 mounts from a Celestron AVX I find lost frames for reasons other than passing clouds to be almost a thing of the past. Satellite trails and other intermittent single frame things usually don't matter because I tend to over collect data and that stuff averages out. Unless its a breezy night I'm generally able to use all the frames.
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I operate at F6.5 with 3nm Chroma filters under a Bortle 9 at unity gain. Exposure time ranges between 600s-1200s and still, the nebula signal only occupy a very tiny percentage in the very lower bound of the histogram but not extreme enough for me to raise the gain.
Look, its not just a matter of swamping read noise. If your exposure time or gain is so low that even 16bits numbers doesn't have enough precision to distinguish between two adjacent signal intensity levels, then even stacking won’t help.
The only reason I'd make it shorter than the exposition time I'm really looking for is if the integration time I'm shooting for would force me to have too few subs for the rejection algorithm.
If you plan for only 5 hours of data on a filter, 1200s exposure gives you only 15 subs. That's too little for me.
Look, its not just a matter of swamping read noise. If your exposure time or gain is so low that even 16bits numbers doesn't have enough precision to distinguish between two adjacent signal intensity levels, then even stacking won’t help.
Himanshu Pandey:
What's the benefit of keeping the subs short if you have the headroom on the camera? Seems an odd way to use your camera.
The only reason I'd make it shorter than the exposition time I'm really looking for is if the integration time I'm shooting for would force me to have too few subs for the rejection algorithm.
If you plan for only 5 hours of data on a filter, 1200s exposure gives you only 15 subs. That's too little for me.
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Questions like this come up regularly and if there is tons of theory about it and calculators of sorts. However, there is also a practical approach to this. And that is that you don't want signal buried into the noise on the low end and not clipped on the high end.
Low end:
Today's cameras have such low noise levels, that your noise will be mostly background noise. So expose long enough that your signal comes out of the background. High dynamic range helps to pick up details from dark areas. Bright objects and fast telescopes expose a bit shorter and fainter objects and slower scopes expose a bit longer. But in the end anywhere between 1-5 mins is probably enough.
High end:
This is where full well depth comes in. The more the better. Undersampled and fast setups are more prone to clipping on the high end. So if your system clips more easily perhaps better to stay at 1-2 mins rather than 5 mins.
Gain:
For your camera, Gain 0 has the highest gain and largest full well depth, so is best to use overall, at least for broadband. Narrowband can often use a bit of boost in signal, in order to pick up enough signal to be measurable with decent precision even with a 16-bit camera, like was mentioned above. So a higher gain often works better. Gain 100 is perfect as that has almost the same dynamic range as gain 0. And clipping in narrowband is almost never an issue, so the lower full well depth is not a problem.
Narrowband exposure:
In most cases you will see that even at gain 100, narrowband signal is rather weak, so you probably want to use exposures more in the 5-10min range. This time it is not only dependent on speed of telescope and brightness of target, but also on bandwidth of your filters, quality of mount, shielding of wind etc. Risk of failed frames increases significantly with exposure time. Going higher with gain than 100 does not give you much benefits. Going longer than 10 minutes often only makes sense if you have very dark skies and a very stable setup.
Low end:
Today's cameras have such low noise levels, that your noise will be mostly background noise. So expose long enough that your signal comes out of the background. High dynamic range helps to pick up details from dark areas. Bright objects and fast telescopes expose a bit shorter and fainter objects and slower scopes expose a bit longer. But in the end anywhere between 1-5 mins is probably enough.
High end:
This is where full well depth comes in. The more the better. Undersampled and fast setups are more prone to clipping on the high end. So if your system clips more easily perhaps better to stay at 1-2 mins rather than 5 mins.
Gain:
For your camera, Gain 0 has the highest gain and largest full well depth, so is best to use overall, at least for broadband. Narrowband can often use a bit of boost in signal, in order to pick up enough signal to be measurable with decent precision even with a 16-bit camera, like was mentioned above. So a higher gain often works better. Gain 100 is perfect as that has almost the same dynamic range as gain 0. And clipping in narrowband is almost never an issue, so the lower full well depth is not a problem.
Narrowband exposure:
In most cases you will see that even at gain 100, narrowband signal is rather weak, so you probably want to use exposures more in the 5-10min range. This time it is not only dependent on speed of telescope and brightness of target, but also on bandwidth of your filters, quality of mount, shielding of wind etc. Risk of failed frames increases significantly with exposure time. Going higher with gain than 100 does not give you much benefits. Going longer than 10 minutes often only makes sense if you have very dark skies and a very stable setup.
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