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ASI071MC-Cool First Light report

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#1 Midnight Dan

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Posted 05 February 2017 - 02:15 PM

So, I received my new ASI071 one-shot color camera over a month ago.  But the weather here is typical for our winters – one big, continuous cloud bank punctuated with very rare nights of clear skies.  As a result, I did some general indoors testing and dark testing, got my USB configuration upgraded, and waited for a clear night.  One finally arrived on Jan 15.  It was very cold though so I didn’t want to spend much time outdoors, and the moon was about 85% illuminated so I just went for the brightest target, Orion.  Wasn’t expecting too much so didn’t set up for a full night of imaging.  This was just a test run of the new camera.

 

But to back up a bit, I actually did get a short clear break about a week before that, just for a couple hours, and was able to do some test exposures  in an effort to see where I was in relation to Jon Rista’s 20xRN rule (20 times the Read Noise).  I was just aiming at a random star field. 

 

I first needed to figure out how to set gain and offset.  There are 3 data points provided in the driver settings as potential starting points:

 

• Maximum Dynamic Range: 0 Gain, 8 Offset
• Unity Gain: 90 Gain, 20 Offset
• Minimum Read Noise: 240 Gain, 65 Read Noise

 

Using the chart on the ZWO site, I could determine the real gain (Electrons per ADU) and Read Noise for various gain settings.  The offset I used was just interpolated between the three settings provided by ZWO in the driver.  I then calculated the 16 bit value I would shoot for in SGP for the 20xRN.  I tried to get an exposure time long enough to produce a mean value in SGP that was greater than or equal to 20xRN, and short enough to saturate only a few stars of the brightest stars at most.  Here’s the results:

 

Screen%20Shot%202017-02-05%20at%2012.42.

 

I calculated the 20xRN value for a variety of gain/offset settings, but did not test them all.  The last two columns are the test data.  Note that I was able to achieve the 20xRN exposure for all but the 240-gain setting test.  The dynamic range had been reduced enough in that test that many stars were saturating unless I kept the exposure short.  In the zero gain test, no stars saturated.  As the gain increased, more stars began to saturate at the 20xRN exposure, with the 150-gain test being barely tolerable.

 

Of course, this test was on a single night with its specific level of skyglow, and nothing in the image except some random stars.  I would have to do some test exposures on the night of actual imaging, but at least this gave me some idea of what I was dealing with.  Normal exposures would likely be in the 3 to 5 minute range, which is about the same as I was experiencing previously with my DSLR.

 

So ... back to Orion on the night of January 15th.  After doing all the upfront testing, I’d know what to shoot for as a mean value in SGP – except I forgot to bring that chart out to the observatory!  Oh well, too lazy to go back in and get it, it’s just a night for a quick test, and I know the Orion core is bright so I’ll just go for a small amount of saturation at unity gain and be done with it.  Took a few test shots and it looked like 2 minutes would be a good exposure.  Shorter than what I was thinking so I figured I probably wouldn’t hit the 20xRN target.  So I set up SGP for 40 lights at 2 minutes.  Went back out an hour and a half later  to run a bunch of flats, bias and dark frames.

 

Next couple of weeks I finally got into PI and started processing this image.  Went through it several times learning the ropes, and this is what I came up with on my last time through:

 

Orion_PI_Small_zpsp7eg49un.jpg

 

Here's the full image in Astrobin if you want a closer look:

get.jpg

 

There’s a couple of things to point out here.  First is the dust on the left.  Remember this was a night with 84% moon illumination?  There’s no way I would have pulled that out of the moon’s LP with my cooled DSLR.  The noise would not have let me stretch it that far.  I’m frankly amazed at what this new camera can do!  The cooling is much more efficient than the DSLR, providing a MUCH lower noise floor.  That lets me use most of the camera’s dynamic range, rather than the lower part of the range being unusable due to noise. 

 

In addition, while both my T3i and the ASI071 have 14 bit data, I used the T3i at ISO 800 to 1600, which limited the dynamic range to 9-10 stops.  The ASI071 at unity gain is giving me 12.5 stops – that’s a huge improvement!  Which brings up the second thing to notice – the core is not blown out.  The Trapezium stars are indeed saturated, but prior to being stretched, the core was easily visible.  Took me a while to learn how to brighten up the dim parts while keeping the core intact, but that’s all from the same image.  So it’s a testament to the dynamic range of this camera that you can cover everything from the core of Orion to the dim outer dust areas in a single exposure.  I could have even done better if I had reduced the gain to say 50 and picked up another half stop of range, at the cost of more exposure time.

 

As for the 20xRN rule, I looked at my subs while processing and found that they had a mean value in SGP of right about 500.  That’s well over the calculated 20xRN target of 296, so I could have reduced my exposures more, still gotten good results, and had the brightest stars a bit less saturated.

 

So I’d have to say I’m a happy camper with this new camera.  It blows away my T3i, despite the fact that I had done a full spectrum modification and added cold-finger TEC cooling.

 

-Dan


Edited by Midnight Dan, 05 February 2017 - 03:39 PM.

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#2 scopenitout

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Posted 05 February 2017 - 03:19 PM

CN member Tolga was a beta tester of this camera. I recall one of the things he didn't like about it was processing the large file sizes.

How about you, Dan, was processing your stated 40 light frames especially difficult, compared to your Canon DSLR?

Did you use Pixinsight for the stacking?

And, did SGP play nicely with the new camera? Specifically, did the rapid exposures of the Frame and Focus Module work ok?

BTW...your first light looks very good.

#3 Midnight Dan

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Posted 05 February 2017 - 03:34 PM

Hi scopenitout,

 

The images are about the same size as my DSLR images, so no real difference in processing them.  I did stack them with PixInsight, which was fairly easy.  40 lights was no big deal, and it seemed to be faster than when I used DSS in the past.

 

I initially had trouble with the camera when connected to SGP and my original wiring setup.  I figured since it claimed to work with USB 2, I could just use my USB 2 hub and cables without issue.  Wrong.  The camera takes a fair amount of power and my hub was not quite up to it.  Plus, the cables were old, not the greatest quality, and the camera wouldn't work well with the longer ones.  I replaced the hub with a Startech industrial USB 3 hub, and the cables with StarTech USB 3 cables.  Problems disappeared.

 

Since my laptop is older and only has USB 2 ports, it has trouble keeping up with the data rate for both the 071 camera and my ASI174 guide camera that I'm running through the 071's built in hub.  I have to go into the driver panels and turn the USB bandwidth limit down to 40 for both, then it works fine.  Otherwise, SGP hangs at downloading.  (SGP really doesn't handle error conditions well) You'd think that limiting the bandwidth that much would slow the download time dramatically, but it doesn't. It does take a little longer, but not that much.

 

Frame and focus works fine for me, but I don't like the lengthy cycle time when downloading the full frame each time. So I first take a single F&F image, select a subsection of it for F&F, and then go into continuous F&F mode.  I can get an image every second or so, which is adequate for focusing.  In any case, no trouble with SGP hanging as long as I set the bandwidths to 40.

 

-Dan



#4 scopenitout

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Posted 05 February 2017 - 03:38 PM

Dan, thank you for that useful information.
Looking forward to seeing some more of your images from the 071.

#5 ManicSponge

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Posted 05 February 2017 - 06:09 PM

 I'll be following this thread closely, Dan. My camera will be here next week, along with the obligatory full moon/clouds/snow/etc.

 I have been looking at SGP, as well as APT, for capture programs. I may try APT first, for the simple reason it looks a lot more like BYEOS in it's layout and functionality than SGP, and BYEOS has been a friend of mine for a long time! Free isn't a bad price, either.

 I've got my fingers crossed that this camera will play nicely with my QHY5Lii guide camera. I've had some odd behavior with it, using my DSLR, but I am running everything through a Startech powered USB hub, and a 30' Tripp Lite USB repeater cable. I'm not opposed to running a second, dedicated USB cable for the guide camera, if I have to (per some of Jon Rista's posts on his 1600 connection woes). All in one would be nice, but I guess I'll be the test pilot for that idea :)

Looking forward to trying this out, and seeing if I can make it work for me.

Regards, Kyle 

 



#6 Jon Rista

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Posted 05 February 2017 - 06:53 PM

CN member Tolga was a beta tester of this camera. I recall one of the things he didn't like about it was processing the large file sizes.

How about you, Dan, was processing your stated 40 light frames especially difficult, compared to your Canon DSLR?

Did you use Pixinsight for the stacking?
 

 

I have also been beta testing this camera. When it comes to stacking, it's about the same as my 5D III. It seems a lot more work than my ASI1600 though. I can stack four channels from the ASI1600 very quickly...and it becomes a long, drawn out task with the ASI071. I think one of the most significant time-consuming steps is the demosaicing step. I use PixInsight, with VNG, and when I'm stacking a lot of frames that step adds a large chunk of time. The largest time consumer, however, was registration. Registration takes a while regardless (it's always the longest step with my ASI1600 data), however it took some two times longer or more with the ASI071. Overall, my pre-processing workflows were about three times longer when processing ASI071 stacks (for the same number of frames). This accounts for a large L stack and three small RGB stacks with the ASI1600. 

 

I don't know if the additional time with registration was simply because of the larger file sizes, or large image sizes, or what...but it definitely takes longer. Combined with the demosaicing step, it's just too much time to use more than about 50 subs, and this camera would definitely benefit from fewer long subs, rather than short subs. That isn't too tall of an order really, though, as you hit unity gain at 90, and you need moderately long exposures there anyway. 



#7 dapalmer

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Posted 05 February 2017 - 07:06 PM

I have seen some really nice images with this camera, this one is among them!



#8 Midnight Dan

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Posted 05 February 2017 - 07:51 PM

I have seen some really nice images with this camera, this one is among them!

I've done a lot of things with my gear over the course of time to try to improve my imaging capability.  All of them have been in the range of incremental improvement to a good solid improvement.  Modifying my Canon T3i was one of those good solid improvements.

 

But moving to this camera is definitely an order of magnitude improvement that added a real "wow" factor.  Far bigger improvement here than anything else I've done.  Really wasn't expecting that from a new camera!

 

-Dan


Edited by Midnight Dan, 05 February 2017 - 10:57 PM.

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#9 Jon Rista

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Posted 05 February 2017 - 08:02 PM

Dan, it's probably the cooling. ;) The dark current on an uncooled T3i, even during winter, can be rather extreme. The sensor in the ASI071 has lower dark current overall, and when cooled to -15C it is about 0.004e-/s. That's better than the ASI1600, and about as good as a Sony ICX sensor. 


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#10 Midnight Dan

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Posted 05 February 2017 - 08:28 PM

 Dan, it's probably the cooling. ;) The dark current on an uncooled T3i, even during winter, can be rather extreme.

 

Yes, but my T3i is NOT uncooled! :-)  I not only modified it with a full spectrum filter removal, but also installed a colder-finger TEC cooling system.  Yet still, the cooling is nowhere near as efficient as the new camera.  So yes, the cooling is definitely the biggest factor. I just didn't realize how big a factor it would be!

 

Also - just noticed that I dyslexified the title of this thread. :-0  is there any way to correct that?  Can't find one.

 

-Dan



#11 Thirteen

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Posted 05 February 2017 - 08:38 PM

PM one of the moderators. They can change it.

Nice image! It seems to work quite well! I keep my eye on this camera. For a portable setup it seems attractive on many levels.


I feel like I should PM you separately regarding that .7x reducer.

#12 ManicSponge

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Posted 05 February 2017 - 09:34 PM

Dan, I see the camera comes with a 1.25" nosepiece. I have an Optolong HA filter, that is 1.25". I know that narrowband and OSC aren't the ideal combination, but it would be fun to play with, and would be something else I could try with zero cash outlay :)

Have you tried this camera with a 1.25" filter? I'm wondering how bad the vignetting would be?

Regards, Kyle



#13 jgraham

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Posted 05 February 2017 - 10:03 PM

Wow, very nice! Very interesting camera as well. Nicely done!



#14 Midnight Dan

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Posted 05 February 2017 - 11:01 PM

Dan, I see the camera comes with a 1.25" nosepiece. I have an Optolong HA filter, that is 1.25". I know that narrowband and OSC aren't the ideal combination, but it would be fun to play with, and would be something else I could try with zero cash outlay :)

Have you tried this camera with a 1.25" filter? I'm wondering how bad the vignetting would be?

Regards, Kyle

Hi Kyle:

 

No I haven't tried the 1.25" nosepiece.  I made a decision long ago to go with a 2" optical path wherever possible to avoid having to purchase both 1.25" and 2" filters for different situations.  I'm guessing that a 1.25" nosepiece would cause vignetting to some degree, but don't know how much.

 

-Dan



#15 Jon Rista

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Posted 05 February 2017 - 11:27 PM

Have you tried this camera with a 1.25" filter? I'm wondering how bad the vignetting would be?

Pretty severe. I have a 1.25" nosepiece for the ASI1600, and even for that camera the vignetting with that adapter is pretty extreme. 



#16 Christian-UAE

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Posted 06 February 2017 - 06:44 AM

  So I set up SGP for 40 lights at 2 minutes.  Went back out an hour and a half later  to run a bunch of flats, bias and dark frames.

 

 

 

-Dan

Hello Dan,

 

At what gain you had set the camera during this 2 minutes exposures ?

 

Thanks

Christian



#17 Midnight Dan

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Posted 06 February 2017 - 10:48 AM

Ah yes, I didn't mention that! I decided to go with unity gain (Driver settings: gain=90, offset=20) as a compromise between exposure length and star saturation (dynamic range).  

 

But if I had that chart out with me when I did my test images for Orion, I would have realized that the mean value in SGP was 500 which was more than I needed.  Knowing that Orion is a high dynamic range target, I would have dropped to a gain of 50 to get a bit more dynamic range.  I probably could have stuck with the 2 minute exposures (or maybe even a bit less), and gotten closer to the target 20xRN value.

 

-Dan



#18 ManicSponge

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Posted 06 February 2017 - 10:59 AM

 

Dan, I see the camera comes with a 1.25" nosepiece. I have an Optolong HA filter, that is 1.25". I know that narrowband and OSC aren't the ideal combination, but it would be fun to play with, and would be something else I could try with zero cash outlay :)

Have you tried this camera with a 1.25" filter? I'm wondering how bad the vignetting would be?

Regards, Kyle

Hi Kyle:

 

No I haven't tried the 1.25" nosepiece.  I made a decision long ago to go with a 2" optical path wherever possible to avoid having to purchase both 1.25" and 2" filters for different situations.  I'm guessing that a 1.25" nosepiece would cause vignetting to some degree, but don't know how much.

 

-Dan

 

 

 

 

Have you tried this camera with a 1.25" filter? I'm wondering how bad the vignetting would be?

Pretty severe. I have a 1.25" nosepiece for the ASI1600, and even for that camera the vignetting with that adapter is pretty extreme. 

 

Thanks, guys. I'm guessing the 1.25" nose piece must be for ROI imaging of planets. I'll be interested to see how this does for planetary work, as well. I'm lacking focal length at the moment, but there may be an Edge HD in my future somewhere.

Regards, Kyle



#19 mahaffm

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Posted 15 March 2017 - 10:54 AM

Hi Dan,

 

Somewhat of a newbie, I do have the ASI071 camera and your report was very helpful. Can you share with us how you calculated the 20xRN and the 16 bit value?

 

Thanks,
Mark



#20 Midnight Dan

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Posted 16 March 2017 - 04:22 PM

Hi Mark:

 

Well, I started with the Read Noise values (in electrons) from the chart on the ZWO site for the camera and multiply that by 20. To convert that to the camera's 14-bit ADU units, you need to divide by the gain in e-/ADU (also from ZWO's chart).  The offset is in ADU units, so you add that to the calculated value.  Finally, you multiply by 4 to convert from 14-bit to 16-bit values.

 

So the equation is:

 

16-bit 20xRN = ( ( (RN * 20) / Gain ) + Offset ) * 4

 

To use the first line in my chart as an example:

 

16-bit 20xRN =( ( (3.3 *20) / 2.7 ) + 8 ) * 4 = 129.778

 

So if you're using a gain setting of zero, and an offset of 8, then you need your exposure to be long enough so that the mean value (which represents mostly the sky background) is about 130.

 

-Dan



#21 mahaffm

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Posted 16 March 2017 - 07:45 PM

Hi Dan,

 

That is perfect, exactly what I was looking for, Thank you. One more question if I may, from you chart/equation I'm running the ASI071 at a gain of 90 and offset of 20 would mean I need a Mean image value to be above this sky background value, in this case 296, How do I determine if I'm over exposing?

 

Thank you,

Mark



#22 Midnight Dan

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Posted 16 March 2017 - 08:40 PM

Hi Mark:

 

Yes, that's correct - at Unity gain (90/20) you want to expose to get a mean value of about 296.  When you overexpose, the bright stars will be saturated.

 

When I start up, I take some test images to determine the right exposure.  To see if I'm overexposing, I look at the brightest stars in the image to see if they are saturated, and how many are saturated.  In SGP, you can move your cursor over the image and the bottom part of the Image Statistics panel will show you the data for a small rectangle of pixels around your cursor.  So I move the cursor to the center of the bright stars to see if I'm getting close to about 65,000 (maximum 16-bit value).

 

In general, it's ok for some of the brighter stars to be saturated.  Its up to you as to how many is acceptable.  I found that when the gain was low, I could expose to the 20xRN level and get no saturated stars.  As I increased the gain, I would get more and more saturated stars at the 20xRN level because the dynamic range decreases.  If you really want that extra gain to reduce your exposure time, you'll have to decide what's the best tradeoff for you between saturated stars and gain.

 

I found that unity gain was a pretty good exposure setting for this camera. I'll probably stick with it for most of my imaging.

 

-Dan



#23 mahaffm

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Posted 16 March 2017 - 09:15 PM

Hi Dan,

 

Very very helpful. I use SGP and I'm currently imaging M42 as we speak and was able to do exactly what you suggested. I took my exposure down from 120 secs to 90 and it looks like I can go lower. My mean is running around 750. So I'm sure I can go lower but looking at the various stars, I sampled maybe 30 and the big stars are saturated but most of the "Average" stars are measuring around the 30K to 40K range. So I think for now I'll keep the 90 seconds.

 

Again thank you, the information you supplied was very helpful.

 

Kind Regards,
Mark



#24 anismo

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Posted 16 March 2017 - 09:48 PM

That is a beautiful result Dan. Very smooth and polished processing. This is looking to be another excellent addition in the CMOS line up. 



#25 scopenitout

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Posted 18 March 2017 - 11:32 AM

So Dan...anymore images from your 071?

Particularly, I'd like to see some fainter targets shot with this camera. Most OSC cameras seem to always perform well with brighter objects.


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