#221  
Old 04-06-2016, 02:28 AM
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Shiraz (Ray)
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hot off the press - finally got some sky between the clouds. M83 from 84x1minute subs at gain100 and -15C. Have not yet done any sort of calibration and the setup I was using did not support dither, so the low noise of the camera was advantageous. Processing was alignment, stack, deconvolution based on measured PSF, histogram stretch, very mild noise reduction and a crop to select the most evenly illuminated region. Seeing was average and the EQ8 was only managing about 0.9arcsec RMS in the conditions. Transparency was also nothing better than average. I also have some 30 second subs and they look OK as well - haven't used them yet. The galaxy was also readily visible in 5 second focusing images.

http://astrob.in/full/251238/0/?real=&mod=None

overall, the camera worked well. I was babysitting it to see if any issues arose and caught myself regularly saying B*** heck under the breath as the low noise images poured out. No odd behaviour and there was no sign of fan vibration - also seems that 1.25 filters will be usable, but that decision will await some flat data. Will process it properly at some stage, but wanted to get something up on IIS asap. The attached small image shows the core with a more mild stretch - at 1 minute it was just under saturation levels. The theory works .

So, FWIW, based on Glen's and my images to date, looks to me like:
the camera is very low noise - there is very little dark current, fixed pattern or read noise and there is no issue with "amp glow"
there is no problem with fan vibration
the low read noise really does allow very short subs without loss of final SNR
the effective dynamic range is excellent with a little care
Regards Ray
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Last edited by Shiraz; 04-06-2016 at 08:20 AM.
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  #222  
Old 04-06-2016, 05:02 AM
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Very impressive Ray. A great start.

What would be great also if later if you could do a usual image with your 694 as a comparison.

Greg.
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  #223  
Old 04-06-2016, 06:19 AM
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The image looks great Ray.

No doubt this camera is excellent value for money
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  #224  
Old 04-06-2016, 09:10 AM
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to go with earlier M83 post, here is a screen shot of a single sub (STF stretch, still with bias) showing vignetting with the 1.25 filters - it doesn't look too bad and the filter wheel can be moved about 10mm closer to the chip, which will help further.
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  #225  
Old 04-06-2016, 09:41 AM
glend (Glen)
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Nice M83 Ray. I assume 1x1bin. I like the disc gas definition. Can you run put up the 30 sec version? With your Gain set at 100, what offset were you using?
I have been reading up on Gain, Offset and Bit Depth and found this article by Carig Stark useful, not saying you need it, but anyone coming from a DSLR background to this camera might find it useful:
http://www.stark-labs.com/help/blog/...nAndOffset.php

East coast low here so I am out of action probably until Tuesday at the earliest.
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Old 04-06-2016, 10:07 AM
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offset 21, 1x1 bin. Craig's article is great, but it deals with getting the best dynamic range in CCD subs. The 1600 allows you to trade off some dynamic range if you wish to use very short subs or get vanishingly small read noise for NB - something CCDs cannot readily do.
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Old 04-06-2016, 10:20 AM
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Very nice Ray! Looks like the camera is performing really well. I am with Greg, would love to see a comparison between this and the 694
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  #228  
Old 04-06-2016, 10:37 AM
glend (Glen)
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Quote:
Originally Posted by Atmos View Post
Very nice Ray! Looks like the camera is performing really well. I am with Greg, would love to see a comparison between this and the 694
Well if they are going to be compared, then try and show short sub performance comparisons as well as long traditional SNR performance. It would be interesting to see if the 694 can stay with the 1600 below 60".
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Old 04-06-2016, 11:08 AM
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Well if they are going to be compared, then try and show short sub performance comparisons as well as long traditional SNR performance. It would be interesting to see if the 694 can stay with the 1600 below 60".
The 1600 will be slightly more resolved due to having smaller pixels, in broadband they should be very similar but the 1600 will be better and picking up very faint things due to the lower read noise. I imagine that most of the galaxy Ray showed above would look the same as they're "brighter" regions.
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  #230  
Old 04-06-2016, 11:27 AM
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This camera is looking very convincing. I'll be very interested to see how it goes with different sized filters. Should I ever try narrow band, I'd want to use 3nm filters, but damn they are expensive.
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  #231  
Old 04-06-2016, 11:34 AM
glend (Glen)
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Originally Posted by bugeater View Post
This camera is looking very convincing. I'll be very interested to see how it goes with different sized filters. Should I ever try narrow band, I'd want to use 3nm filters, but damn they are expensive.
Marty, Jon Rista on Cloudy Nights (post #1404 in the Beta Testing thread) offered this observation about narrowband:

Based on the stacking efficiency charts by Shawnxc, I actually wonder if 300s is more than enough for an ASI with a 7-12nm bandpass. I think for my 3nm filters, I might need up to 600s for OIII an SII. I would actually like to see the same charts that Shawn has produced for the ASI produced for the KAF-8300. So far, I am a believer that 20-60 second subs, depending on sky darkness, are all that is needed for LRGB imaging, so I think the charts model reality well enough to be a good gauge for how long we should be exposing for. It would tell us the sweet spot in exposure time for both cameras.

I use the Baader Narrowband filters (Ha 7nm, OIII 8.5m, and SII 8nm) and they are fine on this camera. Obviously it depends on the target but I find brighter Ha targets like M8, M20, etc are enough with just 60" subs, but agree that OIII and SII can require more time, again depending on the target.

Re filters, most of the beta testers on CN are using 1.25" filters, and they have to be pretty careful about getting the sensor as close to the filter as possible to avoid vignetting. However, I use 36mm filters and there are no concerns.

Last edited by glend; 04-06-2016 at 11:52 AM.
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Old 04-06-2016, 11:46 AM
glend (Glen)
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Just another comment on the comparison with the 694. It is pretty obvious that just about all of the Beta Testing has been done on DSOs, and the planetary capabilities of the 1600 are for the most part ignored. This is, in part, due to the excitement about the low noise, high sensitivity nature of the sensor and system, and the background of the CN testers. Even here on IIS the discussion has be mostly related to DSO performance. This camera, with its very high frame rate video capabilties, pushed through Sharpcap and AutoStakkert is suppose to be an excellent planetary and solar camera as well. Can the 694 play in that space as well?

"One camera to rule them all" maybe a long bow to draw, but for people on a budget looking to try all aspects of imaging, it's not a bad assumption.
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  #233  
Old 04-06-2016, 12:02 PM
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Glen, I wouldn't take too much stock in what those over the big pond are doing. Our skies are better (when it isn't raining!)

Maybe it's a good time to re-read Ray's thread on exposing past the read noise? While the read noise is low with the 1600, it's not zero. You'll want to expose your background beyond the total noise in your subs, for best results.

Personally, I'd be looking at one of these as a less expensive, large, cooled sensor for conventional DSO imaging. In which case, I'd only be interested in using unity gain FWIW.
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  #234  
Old 04-06-2016, 12:07 PM
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Quote:
Originally Posted by glend View Post
Just another comment on the comparison with the 694. It is pretty obvious that just about all of the Beta Testing has been done on DSOs, and the planetary capabilities of the 1600 are for the most part ignored. This is, in part, due to the excitement about the low noise, high sensitivity nature of the sensor and system, and the background of the CN testers. Even here on IIS the discussion has be mostly related to DSO performance. This camera, with its very high frame rate video capabilties, pushed through Sharpcap and AutoStakkert is suppose to be an excellent planetary and solar camera as well. Can the 694 play in that space as well?

"One camera to rule them all" maybe a long bow to draw, but for people on a budget looking to try all aspects of imaging, it's not a bad assumption.
For planetary the 694 is not in the same league simply for the download speed. the 1600 has a high frame rate where as the 694 has a 2s download. it can be considerably sped up with subframing but not to the same extent.

What the 694 has is a higher QE. I am considering moving over to the 1600 (or at least testing between the two) because the high UV QE of the 694 is playing havoc with my refractor. As a rough guess, the 694 may be 1.5-2x as sensitive to OIII as the 1600. For me the difference between the 694 & 1600 is 250s & 60s (as Ray just showed). Or if run at gain 0, 150s. I personally would run the 1600 at gain 0 as it makes it a camera with 20K well depth and 3.6e- read noise. I prefer having less images to deal with. Could you imagine Rolf having done is 150 hour mammoth runs with 30-60s exposures!
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Old 04-06-2016, 12:15 PM
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I mean no disrespect, Colin, but running the 1600 at less than unity gain doesn't make a lot of sense to me...you can't capture additional dynamic range, whereas with your 694 you get full 16-bit (well, depending on the gain setting). The only thing I can conceive as an advantage is not blowing out any bright stars in the FOV. But that's just me, I'm keen to be educated

If anyone wants to donate their 694 (or 674, I'm not fussy ) to a good home, PM me and I'll send you my address
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Old 04-06-2016, 12:29 PM
glend (Glen)
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I am sure Ray remembers the thread he started back in March 2013 about where the 694 would fit in, and comparisons made at that time with the 8300. Once again the 8300 and 694 are benchmarks for the 1600. So Ray, care to comment on the 1600 visa vie the two venerables?
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Old 04-06-2016, 12:31 PM
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Originally Posted by Camelopardalis View Post
I mean no disrespect, Colin, but running the 1600 at less than unity gain doesn't make a lot of sense to me...you can't capture additional dynamic range, whereas with your 694 you get full 16-bit (well, depending on the gain setting). The only thing I can conceive as an advantage is not blowing out any bright stars in the FOV. But that's just me, I'm keen to be educated

If anyone wants to donate their 694 (or 674, I'm not fussy ) to a good home, PM me and I'll send you my address
The only reason I would consider changing from the 694 is because of its blue response not playing well with refractors (I get large blue halos from UV detection).

After doing a bit of reading random threads on CN, ZWO mentioned that the sensor in this comes from an OMD-D-E-M1.
http://www.sensorgen.info/OlympusOM-D-E-M1.html
As Olympus use this sensor in a few of their cameras, the M10 (http://www.sensorgen.info/OlympusOM-D-E-M10.html) has a reported higher QE so I am going to assume that this is more correct for the ASI1600. 60% peak.

Eyeballing the charts, that gives it a QE of ~42% in SII, ~46% Ha and 54% in OIII.
694 (eyeballing chart for QSI660) is 65% in Ha, 75% in OIII and 61% in SII.
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  #238  
Old 04-06-2016, 12:37 PM
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Yeah the allure of something new and shiny is overwhelming, but a 694 is a fantastic (formidable?) imaging sensor FWIW.
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  #239  
Old 04-06-2016, 01:04 PM
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Shiraz (Ray)
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Originally Posted by glend View Post
I am sure Ray remembers the thread he started back in March 2013 about where the 694 would fit in, and comparisons made at that time with the 8300. Once again the 8300 and 694 are benchmarks for the 1600. So Ray, care to comment on the 1600 visa vie the two venerables?
Glad to if you think it would be useful, but it will take a bit of thinking and that seems to be getting harderer - this camera requires some new assumptions - some of which are not obvious. In the meantime, a few thoughts:

If you get to sky noise limited conditions, the 694 will win because of it's high QE and the 8300 and 1600 will come second. However, for broadband, the 1600 needs maybe 1 minute subs, the 694 needs 5 minutes and the 8300 about 20 minute subs to get to sky limited performance with typical gear under typical sky, so there are very significant ancillary equipment/mount implications in favour of the 1600 - a low end mount might do well enough, plus you can sell your OAG,ONAG,large pixel guider etc and get a cheap guidescope with a QHY5L2.

With 3nm narrowband imaging, the 1600 might get to sky limited in 10-20 minutes, but neither of the other two will ever get there (practically) under dark sky (from memory, I think it required about 6 hour subs for the 8300). That gives the 1600 a big advantage if the sub lengths are limited to maybe 30 minutes, since the 1600 read noise will not intrude into an image - there will only be shot noise - but the others will have read noise as well (lots of it in the case of the 8300). Images from the 1600 should be deeper than those from the 694 and much deeper than those from the 8300. In heavy light pollution, all of the cameras should make it to sky-noise limited performance with practical sub lengths, so the 694 will win (ie require less total integration time) due to it's better QE. But the 1600 will still have the advantage of needing vastly shorter subs than the other two.

The 1600 is not magic. Sky glow, shot noise and dark noise will still ultimately limit what it can do, just like the other cameras. However, it has such low read noise that it can operate in modes that are simply not possible with the other two cameras - and that opens up lots of new opportunities. But if you are conservative by nature, you can still use it the old way - long subs will just give you a higher res version of the 8300.

Last edited by Shiraz; 04-06-2016 at 01:38 PM.
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  #240  
Old 04-06-2016, 01:23 PM
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offset 21, 1x1 bin. Craig's article is great, but it deals with getting the best dynamic range in CCD subs. The 1600 allows you to trade off some dynamic range if you wish to use very short subs or get vanishingly small read noise for NB - something CCDs cannot readily do.

Hi Ray,

I am not sure how you concluded that from Craig's article. The gain and offset had a procedure to be set to keep the resulting images within the 65535 levels that 16 bit gives. Its not dependent on exposure length but setting what the sensor will record without loss of data.

So you are saying shorter exposures at higher gain may clip dynamic range but you get better read noise with the higher gain settings?

Just out of interest what are the read noise values for this camera at different gain settings. is that known? I have read figures from 1.6 to 3.6.
Which by the way in CMOS world is quite high. I should look for it but I did read a test of the Sony A7r2 BSI 42.4mp full frame sensor read noise at some ISO levels as .3 electrons. This makes sense as OMD cameras are often reported by owners as noisy even at low ISO. The point here is not to take anything away from the ASI1600 as its a new paradigm and way cleaner than CCDs but more imagine one of those Sony full frame BSI babies in a cooled body like the ASI? Wow.

But this camera is 12 bit? Or is it 12 bit output but 16bit internal processing? (For example Sony A7 cameras output is 12 bit sometimes depending on features activated but the processing pipeline is 14 bit).

How many levels is 12 bit is 4096 levels of brightness.14 bit is 16384 levels of brightness.

Greg.
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