#261  
Old 05-06-2016, 05:36 PM
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Slawomir (Suavi)
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Thank you Ray for helping me to get a better understanding of functioning/parameters of the new ASI camera

Actually I have never measured background signal before, so it was interesting to notice that in my 10-minute subs captured with 3nm Ha there is 102 ADU of background signal give/take a few ADUs. Gain is 0.26. That's a lot of unwanted signal!

Also, while I had my camera powered up, I wanted to see how a 300s dark from my current camera compares with the one from ZWO's website, so I just took a 300s one and did a bit of measuring on both using stats tool in PI. By no means I want to judge which one is better, I simply want to know how things are shaping up with the newcomer from ZWO. I can see that AVD, MAD and mean ADU values differ for both cameras, but I am not sure whether these should be somehow scaled to be able to truly compare the data?

Anyway, here are the results I've got:

AVD = Average Absolute Deviation
MAD = Median Absolute Deviation


ASI1600
entire 300s dark at -25C (from ZWO website)
Mean 154.3
AVD 14.9
MAD 23.7
Min 17.0
Max 23937.0

QSI690 (gain 0.26)
entire 300s dark at -25C
Mean 502.9
AVD 13.2
MAD 11.9
Min 419.0
Max 25952.0

ASI1600
a small central area of a 300s dark
Mean 152.7
AVD 14.1
MAD 23.7

QSI690 (gain 0.26)
a small central area (the same size) of a 300s dark
Mean 503.2
AVD 13.2
MAD 11.9
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  #262  
Old 05-06-2016, 06:53 PM
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Quote:
Originally Posted by Slawomir View Post
Thank you Ray for helping me to get a better understanding of functioning/parameters of the new ASI camera

Actually I have never measured background signal before, so it was interesting to notice that in my 10-minute subs captured with 3nm Ha there is 102 ADU of background signal give/take a few ADUs. Gain is 0.26. That's a lot of unwanted signal!

Also, while I had my camera powered up, I wanted to see how a 300s dark from my current camera compares with the one from ZWO's website, so I just took a 300s one and did a bit of measuring on both using stats tool in PI. By no means I want to judge which one is better, I simply want to know how things are shaping up with the newcomer from ZWO. I can see that AVD, MAD and mean ADU values differ for both cameras, but I am not sure whether these should be somehow scaled to be able to truly compare the data?

Anyway, here are the results I've got:

AVD = Average Absolute Deviation
MAD = Median Absolute Deviation


ASI1600
entire 300s dark at -25C (from ZWO website)
Mean 154.3
AVD 14.9
MAD 23.7
Min 17.0
Max 23937.0

QSI690 (gain 0.26)
entire 300s dark at -25C
Mean 502.9
AVD 13.2
MAD 11.9
Min 419.0
Max 25952.0

ASI1600
a small central area of a 300s dark
Mean 152.7
AVD 14.1
MAD 23.7

QSI690 (gain 0.26)
a small central area (the same size) of a 300s dark
Mean 503.2
AVD 13.2
MAD 11.9
Thanks very much for the info Suavi.

if you wish to do a direct comparison, I think that you need to get all of the data into electrons and account for the different read noise (the 1600 at the gain used for the ZWO dark has >3.5 electrons read noise). Actually, thinking about it, an apples-to-apples direct comparison is likely to be quite difficult/impossible - there are just too many variables with the 1600. eg, setting the gain on the 1600 to give similar characteristics to the 690 may not be optimum for the 1600. Nonetheless, your results at least show that the two cameras are not different by orders of magnitude, so there is nothing drastically wrong with the 1600.

If your NB background is 100ADU at 0.26, you have 26 electrons sky background. That is more than the brightest dark current region in my 1600, so, for reasonable QE in the 1600, sky noise in your system would overwhelm much of the extra noise from the "glow" in a 1600 - should you ever decide to try one - but why would you with your nice camera.

edit: I am surprised that the MAD values do not change with region selection - not sure what that means.

Last edited by Shiraz; 06-06-2016 at 05:39 AM.
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  #263  
Old 05-06-2016, 07:17 PM
glend (Glen)
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Ray are you using SGP to run the ASI1600? I am using SGP with absolutely no issues, but apparently the CN guys are having problems with it failing. I am still using just the supplied usb3 cable but those guys have powered hubs and active cable extensions etc. I have found SGP is fine doing multi-layered sequences, with filter swaps ahead of shooting lights, swap again, etc all unattended. Framing and focus is causing crashes so they say, yet i have no such issues. Strange.
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  #264  
Old 05-06-2016, 07:53 PM
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Glen, I haven't been able to get SGP running smoothly with the 1600 yet - it all seems to be USB related (slow downloads, inability to use USB2 etc) and I hope the latest setup using just the supplied USB3 cable will do the job (testing tomorrow night). I initially set it all up with Nebulosity and am glad I did - that has worked OK, with the exception of the focusing routine.

I had hoped to just plug the new camera into the existing USB2 hub and accept slower downloads than the maximum that the camera is capable of - but that didn't work at all. I guess that my current H694 generates about 1mpix of data per second, whereas the 1600 can generate up to about 400mpix per second, so it is not all that surprising that there are some teething problems on changing over. Hopefully ZWO will put in a bit of time making the camera play nicely with USB hubs and extension cables, but at least there are some mixes of hardware and software that work reliably in the meantime.

Last edited by Shiraz; 06-06-2016 at 05:48 AM.
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  #265  
Old 06-06-2016, 05:43 AM
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for info, tried using the 1600 with cooling off (eg as you might use for planetary). Nebulosity objected to the data generated at high gain with the standard 21 offset and I had to increase offset to 50 to keep the noise from driving the ADU values into negative territory.
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  #266  
Old 06-06-2016, 06:08 AM
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Slawomir (Suavi)
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Quote:
Originally Posted by Shiraz View Post
Thanks very much for the info Suavi.

if you wish to do a direct comparison, I think that you need to get all of the data into electrons and account for the different read noise (the 1600 at the gain used for the ZWO dark has >3.5 electrons read noise). Actually, thinking about it, an apples-to-apples direct comparison is likely to be quite difficult/impossible - there are just too many variables with the 1600. eg, setting the gain on the 1600 to give similar characteristics to the 690 may not be optimum for the 1600. Nonetheless, your results at least show that the two cameras are not different by orders of magnitude, so there is nothing drastically wrong with the 1600.

If your NB background is 100ADU at 0.26, you have 26 electrons sky background. That is more than the brightest dark current region in my 1600, so, for reasonable QE in the 1600, sky noise in your system would overwhelm much of the extra noise from the "glow" in a 1600 - should you ever decide to try one - but why would you with your nice camera.

edit: I am surprised that the MAD values do not change with region selection - not sure what that means.
Thank you Ray, that makes sense. As for MAD values, I read somewhere that MAD is a more robust indication of noise than AVD or in particular SD, so perhaps that's why there is no change up to one decimal point and perhaps both darks are very even in terms of their ADU values across the chip
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  #267  
Old 06-06-2016, 07:00 AM
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Quote:
Originally Posted by Shiraz View Post
for info, tried using the 1600 with cooling off (eg as you might use for planetary).
Is there some inherent reason I'm not aware of for planetary imaging that using cooling would not be advantage? That is, why not use the cooling if you've got it on the camera?
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  #268  
Old 06-06-2016, 07:18 AM
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Originally Posted by lazjen View Post
Is there some inherent reason I'm not aware of for planetary imaging that using cooling would not be advantage? That is, why not use the cooling if you've got it on the camera?
What Ray may be getting at is that there is both and cooled and uncooled version of the camera, many planetary imagers end up using uncooled cameras.
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  #269  
Old 06-06-2016, 07:21 AM
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Shiraz (Ray)
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Originally Posted by lazjen View Post
Is there some inherent reason I'm not aware of for planetary imaging that using cooling would not be advantage? That is, why not use the cooling if you've got it on the camera?
Dark current is of no consequence with bright objects, so cooling is not necessary. Turning off the fan will remove any possibility of fan vibration messing up high res images.
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  #270  
Old 06-06-2016, 10:03 AM
glend (Glen)
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Ray i had some problems with Frame and Focus in SGP. Found that if using the loop mode it seemed to over-run the SGP buffer and freeze, but if you use Take One it worked fine. With short framing shots it seemed the next one was trying to download before the previous one had been processed and displayed by SGP. I went to 5" Take One and it works fine. And of course you just push Take One again to get the next one, that delay seems to be all that is needed. No other problems.
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  #271  
Old 06-06-2016, 09:43 PM
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Shiraz (Ray)
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Quote:
Originally Posted by glend View Post
Ray i had some problems with Frame and Focus in SGP. Found that if using the loop mode it seemed to over-run the SGP buffer and freeze, but if you use Take One it worked fine. With short framing shots it seemed the next one was trying to download before the previous one had been processed and displayed by SGP. I went to 5" Take One and it works fine. And of course you just push Take One again to get the next one, that delay seems to be all that is needed. No other problems.
most of SGP has been running OK tonight, except for the focuser, which worked once and then refused to function again - I had the 1600 on its own USB3 socket, but it still managed to interfere with the stuff running off USB2 (or that is what appeared to happen). I wish I knew enough to understand what is going on.
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  #272  
Old 06-06-2016, 10:53 PM
glend (Glen)
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Ray there is a thread on CN about SGP and the 1600. Sam from ZWO jumped in and gave an explaination on how the 1600 uses and manages usb3, worth reading.
Also Rista seemed to traced his SGP hang problems to his habit of paging through collected images while a sequence was running, something i do not do. I suppose having lots of memory and storage encourages turning everything on. Coming from a programming background when memory and storage were very limited, i tend to do one thing at a time using as little resource as i can.

Some of their (CN's), testing seems to drifting towards exploring the limitations of the camera in areas like 3nm narrowband subs of 900s+ duration at zero gain. I guess if you suffer under extreme light pollution that might seem to be a good idea but no relevance for me. I like to be able to shoot reasonable narrowband with 60" subs. Certainly points out the flexibility of the camera i suppose, but their maybe others better suited to that operation mode.

Last edited by glend; 07-06-2016 at 09:29 AM.
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  #273  
Old 07-06-2016, 12:30 PM
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Originally Posted by glend View Post
Some of their (CN's), testing seems to drifting towards exploring the limitations of the camera in areas like 3nm narrowband subs of 900s+ duration at zero gain. I guess if you suffer under extreme light pollution that might seem to be a good idea but no relevance for me. I like to be able to shoot reasonable narrowband with 60" subs. Certainly points out the flexibility of the camera i suppose, but their maybe others better suited to that operation mode.
I think it's the opposite, actually. I image in fairly dark skies with a reasonably low read noise Sony sensor, and I would have to be doing insanely long exposures with 3nm filters to not be read noise limited. There's no point in high light pollution scenarios because you swiftly get past the "read noise limited" point, and once you have, it's just about total integration time.

In other news, looks like the Trius is now sold, so I'll hopefully have a 1600 on the way soon.
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  #274  
Old 07-06-2016, 02:19 PM
glend (Glen)
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Originally Posted by codemonkey View Post
I think it's the opposite, actually. I image in fairly dark skies with a reasonably low read noise Sony sensor, and I would have to be doing insanely long exposures with 3nm filters to not be read noise limited. There's no point in high light pollution scenarios because you swiftly get past the "read noise limited" point, and once you have, it's just about total integration time.

In other news, looks like the Trius is now sold, so I'll hopefully have a 1600 on the way soon.
Yeah, i admit i don't understand the reason behind it, i assumed it was because of his light pollution situation. And we all know about assuming......

Glad to hear about the camera news. A novice like me needs all the experienced help he can get. I am sure you will enjoy it.
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  #275  
Old 07-06-2016, 03:04 PM
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Just did some quick calculations, the difference between the 1600 and the 694 (674 as well as it is just a smaller version) with 3nm narrowband filters is negligible. The 1600 has lower read noise at gain 0 (3.6e- vs the 4.8e- I get) but also has smaller pixels (3.8 vs 4.54 microns) and a lower QE. Both cameras will require the same amount of time to reach read noise limited under the same situations, with the 1600 at gain 0.
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  #276  
Old 07-06-2016, 03:17 PM
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But...but...but...why would anyone want to image at gain 0
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  #277  
Old 07-06-2016, 04:21 PM
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To prevent highlights from blowing out in a long exposure perhaps?
From what little I have seen of this camera it seems to be its Achilles heel.

Greg.
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  #278  
Old 07-06-2016, 04:35 PM
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But...but...but...why would anyone want to image at gain 0
As you increase the gain it does drop the read noise but the overall dynamic range drops with it. i.e. the read noise falls slower than the decrease in well depth.

Yes you can image at gain 300 with 1s exposures in Lum (gregbradley noted that it clipped the core of M51 even at 1s). Using a 3nm Ha filter, if you can drop the read noise to 0.6e- you need ~50s exposures (at F/5) to be RN limited but your well depth is so shallow that even at that exposure time you're clipping.

To give a bit of a comparison, at gain 0 (where the 1600 has its highest dynamic range) compared to a KAF-16803 on the same telescope, they need about the same exposure time to become RN limited. This is given that the KAF has a RN of 8e- (I believe that RickS mentioned a while back that this is what his PL16803 gets at SRO), this is within a margin of 10% (the 16803 reaches RN limited a fraction quicker without taking dark current into consideration but the 1600 is likely to be lower in that regard) . The 16803 has 5x the well depth however so while the 1600 will clip stars and bright cores (thinking of lagoon, M31, M42 ect) the 16803 will barely notice the difference.
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Old 07-06-2016, 05:00 PM
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Main Sequence Software has a fix for the SGP crash issue and will release a patch in a few days:
http://www.cloudynights.com/topic/53...5#entry7260667
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Old 07-06-2016, 05:17 PM
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Yeah, i admit i don't understand the reason behind it, i assumed it was because of his light pollution situation. And we all know about assuming......

Glad to hear about the camera news. A novice like me needs all the experienced help he can get. I am sure you will enjoy it.
Might just be so they can compare its performance using more traditional sub lengths? I dunno.

Cheers mate, I sure hope I do enjoy it.

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Just did some quick calculations, the difference between the 1600 and the 694 (674 as well as it is just a smaller version) with 3nm narrowband filters is negligible. The 1600 has lower read noise at gain 0 (3.6e- vs the 4.8e- I get) but also has smaller pixels (3.8 vs 4.54 microns) and a lower QE. Both cameras will require the same amount of time to reach read noise limited under the same situations, with the 1600 at gain 0.
Not sure if it's me just misinterpreting your wording or if there's a misunderstanding, but you start off read noise limited and increase sub length to try and overcome that, rather than "reaching" it.

It's also a bit hard to compare the performance of those cameras based off numbers alone because we still don't know the absolute QE.

Quote:
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Main Sequence Software has a fix for the SGP crash issue and will release a patch in a few days:
http://www.cloudynights.com/topic/53...5#entry7260667
That's good news!
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