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Old 28-05-2016, 05:11 PM
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So... anyone wanna buy a SX-674?
I will! Is $20 enough?
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  #162  
Old 28-05-2016, 05:49 PM
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How about $25?
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Old 28-05-2016, 10:01 PM
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Originally Posted by glend View Post
...The beauty of this camera is that you can probably do enough data acquistion in a few hours to build a nice narrowband image. What used to take me three nights with my mono dslr is only going to take a couple of hours now, imho...
I have been following this (and pretty much all the other threads on IIS) and all this narrow band imaging is way over my head. Glen, why will few hours with the new camera work better that few nights with the mono DSLR? Is it just increased sensitivity and lower noise being that much better? Apologies if it is a stupid question but otherwise I will never learn.
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  #164  
Old 29-05-2016, 09:18 AM
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While waiting patiently for Australia post to move my camera from NSW to SA, have been analysing some dark image data presented on CN to try to understand the "amp glo" that some users are reporting. I had to make a few assumptions about how the camera and software works, but if I got anywhere near right, the glow is just slight variation in dark current across the chip (due either to peltier temperature variations or to the chip itself).

my best guess is that, at the tested -15C, the dark current varies (over the specific chip where data was available) from about 0.013 e/s/pix in the centre to 0.021 in the brightest of the "glow" on one edge. This level of dark current is not as good as the Sony CCDs, but slightly better than the Kodak ones - ie neither the dark current nor noise from the "glow' should be a major issue. However, there may possibly be some difficulty with scaling darks, if the start point varies with position on the chip. Real darks taken at the true temperature may possibly be best with this camera. Of course, the dark current is still very low and it may be possible to get good results by ignoring dark calibration altogether and relying on dithering. That could be very useful if the datasets get big (eg with short subs)

Last edited by Shiraz; 29-05-2016 at 10:02 AM.
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  #165  
Old 29-05-2016, 10:36 AM
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Originally Posted by luka View Post
I have been following this (and pretty much all the other threads on IIS) and all this narrow band imaging is way over my head. Glen, why will few hours with the new camera work better that few nights with the mono DSLR? Is it just increased sensitivity and lower noise being that much better? Apologies if it is a stupid question but otherwise I will never learn.
Not a stupid question at all.

The new camera appears to have some excellent incremental improvements but it won't be orders of magnitude better than the old one and won't produce images of the same depth in a small fraction of the integration time.

Cheers,
Rick.
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  #166  
Old 29-05-2016, 02:01 PM
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I ran some narrow band tests on M8 last night. Shot 10 x 60" Ha subs, 10 x 60" OIII subs, and 10 x 60" SII subs. I also shot Darks and Bias subs to match. I ran this all using SGP with no issues at all. I have upgraded my ASCOM Platform to the most recent release (6.2) and downloaded the newest ASI1600 driver update. The plan was to shoot a complete narrow band test sequence using 60" subs, with camera gain set at 60 (the recommendation of Jon Rista (CN), and sensor temp at -25C. I also shot the same set of narrow band subs at 90". Not surprisingly it does not take long to run this sequence using these short subs, and frankly I was surprised by the outcome.

I stacked the 60" sets and the 90" sets in DSS, with the Darks and Bias frames (no flats at this time).
Took the final Ha images (60" and 90") out to Photoshop and despite the initial dark appearance when stretched they leap out.

I won't say I am happy with the one linked here, the 60" example (the centre is blown out) but it gives you an indication of what this camera can do with such short narrowband subs. My processing skills are probably not up to handling this.
I will be continuing my testing this coming week. I may get to the point of producing a false color combined image of M8, as the OIII and SII data sets are already gathered at 60" and 90". I am tempted to go to 30" subs, in larger numbers, but would welcome any suggestions.

Link to Astrobin M8 Ha detail page:
http://www.astrobin.com/250623/

Full size here:
http://www.astrobin.com/full/250623/None/
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  #167  
Old 29-05-2016, 03:31 PM
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Great stuff Glen. That's an impressive M8 for only 10 minutes total exposure time.

The central area is very bright. Is the core data still there and can be retrieved with shadows/highlights or is it gone? 60 seconds is such a short exposure time for the core t blow out. Perhaps the gain should be reduced when imaging a neb with a bright core to preserve the highlights.

Greg.
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  #168  
Old 29-05-2016, 06:26 PM
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Thats impressive! What sized aperture/ focal length is the scope?

Trent
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Old 29-05-2016, 07:07 PM
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The scope used is a Skywatcher MN190 Mak-Newt, f5.3.

Greg i am going to reduce gain and reshoot. The charts put up on CN suggest maximun SNR occurs by the time you get to 30 seconds, and there is no improvement beyond 60 seconds. So in theory more shorter subs to build integration time but the trade off is final file size.
I am sure processing experts could get better results with my data, i am really just voming to grips with it.
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  #170  
Old 29-05-2016, 10:44 PM
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Using the graph that Shiraz posted.
http://www.iceinspace.com.au/forum/s...&postcount=157

It should still take about 6 minutes to become read noise limited, even at ~1.6e-. I based the calculations off of my previous setup was at F/5.7 and a KAF-8300 with a read noise of 8.5e-. It needed 90-120 minutes to reach that point!

Last night I did 10 minute subs with my ICX694 (more sensitive, smaller wells and larger pixels) and it wasn't saturated at the core. Sounds like the gain may be a tad high but you can also throw in some 1-10s subs to tone that down during processing.
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Old 29-05-2016, 11:25 PM
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Thanks Colin for that suggestion. I agree the gain is the probable issue. I have been shooting NGC6188 tonight with the gain turned way down, and initial looks at single subs show no saturation of the core area. Interestingly i was having a look at the camera presets, and one of these is HDR (High Dynamic Range) and the gain in that preset is almost zero. I will post up NGC6188 tomorrow.
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  #172  
Old 30-05-2016, 07:29 AM
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Originally Posted by Atmos View Post
Using the graph that Shiraz posted.
http://www.iceinspace.com.au/forum/s...&postcount=157

It should still take about 6 minutes to become read noise limited, even at ~1.6e-.
how did you determine that from the graph?
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  #173  
Old 30-05-2016, 07:57 AM
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I just used the graph to get the figures, then did some calculations against figures I'd calculated a while back. It's not directly from the graph
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  #174  
Old 30-05-2016, 08:01 AM
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Originally Posted by Atmos View Post
Using the graph that Shiraz posted.
http://www.iceinspace.com.au/forum/s...&postcount=157

It should still take about 6 minutes to become read noise limited, even at ~1.6e-. I based the calculations off of my previous setup was at F/5.7 and a KAF-8300 with a read noise of 8.5e-. It needed 90-120 minutes to reach that point!
this is one of the two areas of great interest with this camera - if you accept that most NB imagers under reasonable sky will not be sky-limited, the one with lowest read noise will have the deepest images (dark noise and QE being equal) .

edit: and the other area of interest is the ability to use short subs with broadband and still get comparable SNR results to those from conventional cameras with long subs (sky noise and dark current will still dominate, so there are no SNR advantages, but there are possibly major ancillary advantages from short subs)

Last edited by Shiraz; 30-05-2016 at 08:54 AM.
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  #175  
Old 30-05-2016, 08:16 AM
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this is one of the two areas of great interest with this camera - if you accept that most NB imagers under reasonable sky will not be sky-limited, the one with lowest read noise will have the deepest images (dark noise and QE being equal) .

edit: and the other area of interest is the ability to use short subs with broadband and still get comparable SNR results to those from conventional cameras with long subs (there are no SNR advantages, but there are ancillary advantages from short subs)
That is true I wonder how it would go with combining an image that mostly has a gain of 250 with 5min narrowband subs and then a couple of gain 0 5min subs to collect everything other than the faint background.
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Old 30-05-2016, 09:08 AM
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How about $25?
naah, keep it. The QEs of the Sony CCDs still give them a significant edge in conventional imaging with medium size scopes. The big Kodak chips also still have their place because they are best matched to large, long focal length scopes or widefield with scopes like the FSQ106.

However, the 1600 opens up some entirely new ways of doing things with medium size scopes and even camera lenses (including high resolution DSO, solar and planetary imaging) and doesn't appear to give up much/any performance in conventional long-sub DSO imaging, if you want to use it that way.

Mine just arrived at the local PO, so now begins the process of changing cameras and sorting out all the little issues like focal plane tilt, vignetting, software etc - groan. One nice thing though is that the back focus is almost identical to that of the 694, so, for initial testing, I will just be able to unscrew one camera and screw on the other (that's the theory anyway)

Last edited by Shiraz; 30-05-2016 at 09:31 AM.
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  #177  
Old 30-05-2016, 09:31 AM
glend (Glen)
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I have pulled down my narrowband sub of NGC6188, which was previously posted in this spot, it was rubbish and not worth posting, it is gone from Astrobin as well. The combination of low gain (30), narrowband, and short sub just did not generate enough signal. I will rerun it at some point but with a higher gain setting.

Last edited by glend; 30-05-2016 at 02:41 PM.
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  #178  
Old 30-05-2016, 09:38 AM
glend (Glen)
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Mine just arrived at the local PO, so now begins the process of changing cameras and sorting out all the little issues like focal plane tilt, vignetting, software etc - groan. One nice thing though is that the back focus is almost identical to that of the 694, so, for initial testing, I will just be able to unscrew one camera and screw on the other (that's the theory anyway)
Well Ray, good to hear it has arrived. I will be expecting some images tomorrow morning! Have fun.
PS, it would be nice to get your test results on M8 to compare settings, processing, etc.
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  #179  
Old 30-05-2016, 09:43 AM
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I've been following this thread with interest.

It seems to me the following are critical with this camera:

1. Highlights will blow out if the gain is too high. I think gain is the same as ISO on a digital camera so then when you increase the gain you lower the dynamic range. Also typically there is usually a sweet spot in the ISO range of a digital camera. Where the signal is boosted enough to raise shadows but not introducing much noise and not lowering dynamic range too much.

So think in terms of ISO and you would aim for the lowest ISO to get the shot as noise is lowest at lowest ISO and dynamic range is greatest. If you look at dynamic range graphs of digital cameras you'll see its not a straight line drop with increases in ISO. It tends to worsen more quickly the higher you go.

From what I have seen so far this seems to be the most critical point as 2000x 1 second subs at high gain of M51 with a totally blown core and surrounds is never going to cut it against a high quality CCD camera.

2. Again the low read noise is probably down with the low gain as the higher gain probably amplifies all the noise including the read noise.

One way of working out the optimum gain (ISO) for this sensor would be to look at the DXO scoring for the EM1 this sensor came from. They measure what is the highest ISO you can use before image degradation starts. I haven't looked it up but its probably around ISO1200 for a small sensor like this. So trying to relate that to the gain settings you might be able to find a table of gain and ISO from someone who tests various cameras that way.
It would be valuable to know.

Most DSLR imagers use around ISO800 when stacking lots of images so whatever that equates to would be good to know also. Its probably quite low.

It seems that gain control is a potential image wrecker and should be treated with a little is a lot type of approach and less is better.

Greg.
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  #180  
Old 30-05-2016, 10:00 AM
glend (Glen)
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Thanks Greg, I used to shoot ISO 800 on my 450D as it was the 'sweet spot' for that sensor, but cooling it allowed me to get up to ISO1600 without too much degradation (and was a necessity for narrowband with that camera).

I am waiting for Shawn (CN) to send me a chart he is making up for me, specific to my scope fl, of SNR performance at various sub lengths (although it can be inferred from his other charts). However, no one seems to be addressing gain/preset influence on performance. Jon Rista has mentioned he thinks 60 is the 'sweet spot' but I would suggest it depends on the target to some degree.
There are still not enough ASI1600Ms getting into the hands of testers (most of the US guys that bought through retailers still have not received any delivery advice, other than the Beta Testers, there are a few that ordered direct that now have them but they are hampered by weather and light pollution so far).

Unfortunately, I am probably the last guy to be an early tester of this camera as I am such a hacker when it comes to capture and processing. I can't wait for Ray to get stuck into it.

Last edited by glend; 30-05-2016 at 10:28 AM.
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