#241  
Old 04-06-2016, 12:50 PM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is online now
 
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,810
Quote:
Originally Posted by gregbradley View Post
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.
Yep, takes a bit to get the head around, but the read noise decreases as the gain increases. With a CCD the signal to read noise ratio stays much the same as the gain changes - CMOS are completely different beasts in that there is no single "optimum" setting for the 1600, whereas there is for a CCD.

It is all fully documented http://www.iceinspace.com.au/forum/a...e.php?a=199985 - the read noise can be as low as ~1.2 electrons, but you have only 9 bits dynamic range at that gain setting. Sony chips will do the same thing - pity there are no large mono Sony CMOS chips. I think I read somewhere that Sony make about 800,000 image sensors a day, so they may not be all that interested in changing a production line to do a run of a few hundred mono DSLR sensors - I think that it is amazing that ZWO managed to get Panasonic to do it.


The camera has a 12 bit ADC. You end up with 16 bit numbers in the images, so I assume that the software pads out the bottom 4 bits. This is the same as for the 694, except that the 694 has random noise in the bottom 4 bits rather than zeros. In terms of image quality, no practical difference at all - since random noise and zeros are both useless.

Last edited by Shiraz; 04-06-2016 at 03:20 PM.
Reply With Quote
  #242  
Old 04-06-2016, 01:13 PM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 5,486
Quote:
Originally Posted by Shiraz View Post
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.
Ray that is enough of a synopsis for me, thank you. I was not fishing for a thesis.
Reply With Quote
  #243  
Old 04-06-2016, 02:45 PM
Slawomir's Avatar
Slawomir (Suavi)
Amateur Photon Collector

Slawomir is offline
 
Join Date: Sep 2014
Location: Proserpine
Posts: 3,050
Just to add another perspective to this discussion, here is a recent reply from Atik to my enquiry about implementation of the latest CMOS in their cameras:

At this point, we've found that CMOS sensors still don't compete with CCDs in the realm of long exposure, cooled astrophotography. That said, they are improving all the time and we always keep an eye on new technologies that we could use in our cameras - it has the potential to be an exciting few years!
Reply With Quote
  #244  
Old 04-06-2016, 03:16 PM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 5,486
Quote:
Originally Posted by Slawomir View Post
Just to add another perspective to this discussion, here is a recent reply from Atik to my enquiry about implementation of the latest CMOS in their cameras:

At this point, we've found that CMOS sensors still don't compete with CCDs in the realm of long exposure, cooled astrophotography. That said, they are improving all the time and we always keep an eye on new technologies that we could use in our cameras - it has the potential to be an exciting few years!
Lets see what happen to their sales figures, while they are waiting. isn't QHY working on some new CMOS cameras?

Last edited by glend; 04-06-2016 at 03:29 PM.
Reply With Quote
  #245  
Old 04-06-2016, 06:21 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 15,701
Stan Moore the author of CCDstack said long exposures are still an issue for CMOS with banding noise. I thought banding was really only an issue with Canon sensors and even then a thing of the past.


Perhaps that is what Atik are referring to or maybe they simply couldn't get CMOS sensors!

Greg.
Reply With Quote
  #246  
Old 04-06-2016, 06:48 PM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is online now
 
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,810
Quote:
Originally Posted by glend View Post
Lets see what happen to their sales figures, while they are waiting. isn't QHY working on some new CMOS cameras?
Looks like they have some really nice CMOS cameras, including the cost leading minicam5 with a cooled Aptina CMOS and four others with cooled Sony CMOS chips up to 6mp.
Reply With Quote
  #247  
Old 04-06-2016, 07:21 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 15,701
Quote:
Originally Posted by Shiraz View Post
Looks like they have some really nice CMOS cameras, including the cost leading minicam5 with a cooled Aptina CMOS and four others with cooled Sony CMOS chips up to 6mp.
Yeah but they are awfully slow. Their 16200 camera has been under development for what seems an excessive amount of time. Its still not on the market.

Greg.
Reply With Quote
  #248  
Old 04-06-2016, 07:44 PM
bert's Avatar
bert (Brett)
Automation nut

bert is offline
 
Join Date: Mar 2008
Location: Bathurst
Posts: 667
Has anybody done any testing of the ZWO in binned operation?

Was looking at this camera for dual purpose camera. Both 400mm and around 2.8meters (bin 3). Thoughts?
Reply With Quote
  #249  
Old 04-06-2016, 08:40 PM
Slawomir's Avatar
Slawomir (Suavi)
Amateur Photon Collector

Slawomir is offline
 
Join Date: Sep 2014
Location: Proserpine
Posts: 3,050
Quote:
Originally Posted by glend View Post
Lets see what happen to their sales figures, while they are waiting. isn't QHY working on some new CMOS cameras?
I'm sure the latest camera from ZWO represents awesome value and that this camera will be/is a hit among amateur astrophotographers, but there must be reasons why other manufacturers such as Atik, SX, QSI, Moravian, SBIG and FLI are not rushing, to my knowledge, with realising CMOS-based astro cameras
Reply With Quote
  #250  
Old 04-06-2016, 08:50 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 15,701
Quote:
Originally Posted by Slawomir View Post
I'm sure the latest camera from ZWO represents awesome value and that this camera will be/is a hit among amateur astrophotographers, but there must be reasons why other manufacturers such as Atik, SX, QSI, Moravian, SBIG and FLI are not rushing, to my knowledge, with realising CMOS-based astro cameras
It may be they just stick with what they know and what their established markets want. When you consider warranties and problems with software, firmware it would be easier to let someone else do all the beta testing then walk in with a better basic camera platform that takes just about any sensor once the market is established and the beta testing has shown what is needed to be practical.

Its much like Canon and Nikon not rushing in to do a good mirrorless camera leaving Sony, Fuji and Olympus to own that segment and its the only camera market segment that is actually expanding. DSLRs and point and shoots are falling markets due to mobile phones.

Of course SX already does CMOS cameras with their Ultrastar guide/planetary camera.

Greg.
Reply With Quote
  #251  
Old 04-06-2016, 08:57 PM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 5,486
I am far from technical on this topic, but they maybe waiting for sCMOS (Scientific CMOS) development to commericalise. There is one example of a commerical sCMOS chip already available: http://www.scmos.com/

A summary of sCMOS development and goals:

http://www.photonicsonline.com/doc/s...-overview-0001

The ASI 1600 has low noise and sensitivity improvements, and the high USB3 and frame speeds, but sCMOS should be a bigger leap I would imagine. I don't know where the cross over point lies.

Bert, I think there are some 2x2bin examples in the Cloudy Nights Beta Test thread.

Last edited by glend; 04-06-2016 at 09:11 PM.
Reply With Quote
  #252  
Old 05-06-2016, 07:50 AM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is online now
 
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,810
Quote:
Originally Posted by bert View Post
Has anybody done any testing of the ZWO in binned operation?

Was looking at this camera for dual purpose camera. Both 400mm and around 2.8meters (bin 3). Thoughts?
Sounds like an excellent idea, with one minor issue.

I recall reading (somewhere) some ZWO advice that the chip falls back to lower bit depth on binning. Haven't tried it, but even if it is so, you could still use it effectively, because the read noise is low enough for software binning.

Depending on where you set the gain, in software binx3, you could have effective pixels with 11.4 microns pitch, read noise ~ 9e and well depth of ~180,000e. The minor issue would be that you would have to store and process 9x as many subs as you would with on-chip binning.
Reply With Quote
  #253  
Old 05-06-2016, 08:29 AM
Slawomir's Avatar
Slawomir (Suavi)
Amateur Photon Collector

Slawomir is offline
 
Join Date: Sep 2014
Location: Proserpine
Posts: 3,050
Has anyone tried running say a 10-minute dark to check for distribution of ADU values in such dark across the chip? It would be nice to see what happens during longer exposures for those planning to use this camera for narrowband imaging
Reply With Quote
  #254  
Old 05-06-2016, 09:11 AM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is online now
 
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,810
Quote:
Originally Posted by Slawomir View Post
Has anyone tried running say a 10-minute dark to check for distribution of ADU values in such dark across the chip? It would be nice to see what happens during longer exposures for those planning to use this camera for narrowband imaging
I haven't yet Suavi, but 5minute darks dropboxed from a CN post show total underlying noise, (including read and dark) of less than 3 electrons RMS across the whole field. Startling really - it is weird to view a frame with almost zero noise.
Reply With Quote
  #255  
Old 05-06-2016, 09:14 AM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 5,486
There have been long darks run by the Beta Testers on Cloudy Nights. ZWO offers a 5 minute dark link on the product page for the 1600. I have run 5 minute darks myself to check on the rumoured long dark Amp Glow, which i could barely detect at that duration. Amp glow was explored on CN. Since i don't plan on running longer subs it didn't really concern me, and Sam's (ZWO) attitude when asked on the forum seemed to be that it was not significant to be a concern and was easily calibrated out. I believe ZWO released a driver update that reduced the amp glow further.
The narrowband subs i have been running are 60" subs, and i don't know that i would be too concerned about 10 minute performance with this camera.
Reply With Quote
  #256  
Old 05-06-2016, 09:45 AM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is online now
 
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,810
further to that, people have been looking at "amp glow" by stretching darks and noticing some variation in the bias/dark current, probably due to variations in Peltier temperature. What people seem to be neglecting is that the ADU values represent the 12 bit signal from the chip, multiplied by 16 to give the 16 bit ADU values in the subs. The glow that everyone keep quoting is actually on the order of maybe one or two electron or so in 300 seconds - it is the sort of fluctuation that could well be present in all cooled cameras, but this is the first one that has low enough read noise that you can actually see it. Rather than being a fault, it is an indication of just how low the noise is in this camera.
Reply With Quote
  #257  
Old 05-06-2016, 10:09 AM
Slawomir's Avatar
Slawomir (Suavi)
Amateur Photon Collector

Slawomir is offline
 
Join Date: Sep 2014
Location: Proserpine
Posts: 3,050
Quote:
Originally Posted by Shiraz View Post
further to that, people have been looking at "amp glow" by stretching darks and noticing some variation in the bias/dark current, probably due to variations in Peltier temperature. What people seem to be neglecting is that the ADU values represent the 12 bit signal from the chip, multiplied by 16 to give the 16 bit ADU values in the subs. The glow that everyone keep quoting is actually on the order of maybe one or two electron or so in 300 seconds - it is the sort of fluctuation that could well be present in all cooled cameras, but this is the first one that has low enough read noise that you can actually see it. Rather than being a fault, it is an indication of just how low the noise is in this camera.
Agreed.

Such low read noise will easily show the slightest gradients across the chip.

I measured the 300s dark from ZWO website, and the difference in mean ADU value between the darkest and brightest regions in this 300s dark is 26 ADUs, so indeed very low in electrons.

For reference, I attached a result of an extreme stretch of the 300s dark from ZWO website.
Attached Thumbnails
Click for full-size image (300s.jpg)
124.9 KB36 views
Reply With Quote
  #258  
Old 05-06-2016, 12:44 PM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is online now
 
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,810
A far better way to analyse the darks is to use the local SD (excluding outliers). This will provide an idea of the shot noise due to the dark current and you won't pull in any fixed bias structure (which will be subtracted in calibration).

The dark on the ZWO website was taken at an inverse gain of 5, so the difference that you measured in mean values is 26*5/16 or 8 electrons. This is more than that in the CN darks and it could mean an excess noise of nearly 3 electrons RMS if it is dark current and not just bias shift - that is significant, but it would still not be measurable in almost any other camera. To get some idea of the significance of this sort of signal, how much background sky signal (electrons) do you measure with your 3nm filters?

Last edited by Shiraz; 05-06-2016 at 01:23 PM.
Reply With Quote
  #259  
Old 05-06-2016, 01:22 PM
Slawomir's Avatar
Slawomir (Suavi)
Amateur Photon Collector

Slawomir is offline
 
Join Date: Sep 2014
Location: Proserpine
Posts: 3,050
No doubt the supplied dark has extremely low noise, but 8 electrons variation will in some cases (imaging faint nebulae) need to be corrected with darks when using the camera for 5-minute or longer subs in narrowband imaging. Also, since noise goes up with signal, even after applying darks there will probably be somehow higher noise left in those brighter areas?

I am sorry if I am too particular and also too inquisitive, but I like doing my homework before buying. Also, I am specifically interested in this camera's performance in purely narrowband imaging because of intense light pollution in my area plus I simply like narrowband imaging

EDIT: Will need to measure background signal in my subs.
Reply With Quote
  #260  
Old 05-06-2016, 01:29 PM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is online now
 
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,810
Quote:
Originally Posted by Slawomir View Post
No doubt the supplied dark has extremely low noise, but 8 electrons variation will in some cases (imaging faint nebulae) need to be corrected with darks when using the camera for 5-minute or longer subs in narrowband imaging. Also, since noise goes up with signal, even after applying darks there will probably be somehow higher noise left in those brighter areas?

I am sorry if I am too particular and also too inquisitive, but I like doing my homework before buying. Also, I am specifically interested in this camera's performance in purely narrowband imaging because of intense light pollution in my area plus I simply like narrowband imaging

EDIT: Will need to measure background signal in my subs.
Crikey, there is no need to apologise for digging into the detail - too much stuff gets glossed over and then comes home to bite after a purchase is made. The narrowband potential of this camera could be very interesting and it would be great to know how significant the possible "glow" is compared with your sky signal.

edit: just scaled the darks that I do have. Most of the image has negligible dark current at -15, but two fairly small areas have some "glow", that would amount to about 20 dark electrons at the brightest point over 10 minutes (~0.03 electrons/s). That will give excess noise of up to 4.5 electrons RMS in one corner (for comparison though, that much excess noise is a bit less than the read noise from my 694). The rest of the dark has effectively no dark current. I don't anticipate that this will impact significantly on my images, but agree that about 3% of the camera is not quite as good as the rest of it for narrowband. Must measure at 10 minutes rather than scale and also try it at a lower temperature to see if that helps.

Last edited by Shiraz; 07-06-2016 at 08:48 PM.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 11:50 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Advertisement
Astromechanics
Advertisement
Testar
Advertisement
Lunatico Astronomical
Advertisement
Bintel
Advertisement
Astronomy and Electronics Centre
Advertisement