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ASI1600MM Camera Performance

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#76 syscore

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Posted 18 June 2016 - 07:42 AM

Amp glow is heat (IR) based. All it means is that the electronics of the sensor, typically the amplifier section that reads the sensor, is putting off some heat, and even if it is just a little, and even though the sensor is cooled, it will cause some areas of the sensor to be warmer than other areas and those warmer areas will have more dark current than the other areas and appear brighter. It is like taking a thermal image of an object and the temp of the object not being uniform all over.

 

It is unavoidable. CCDs have it as well, but to a lesser extent, at least with CCDs designed for long exposure imaging. I think CCDs are able to contain it better because all of the readout occurs on the edge/corner and that is where you find the glow. I look at it as being just part of the dark current. In fact, you measure it by taking a dark frame and subtracting a bias frame, leaving just the dark current. It is only a problem when it is either excessive or inconsistent. If it is excessive, then it carries with it additional noise and if it is inconsistent, then it can't be completely calibrated out with a dark frame.

 

Personally, all of this glow talk sounds much worse than it is. The sensor isn't perfect, and none are, but it is the size of an 8300 and it is keeping up with an 8300. I appreciate the immense amount of work that Jon has done in measuring the sensor. It will help everyone who uses the camera. But the more pressing issue is getting the drivers to work consistently, and progress seems to be being made on that. Or the users are exhausted and just not complaining as much. :)


Edited by syscore, 18 June 2016 - 07:44 AM.


#77 Jon Rista

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Posted 18 June 2016 - 08:42 AM

I was going to dive into a few of my books tonight as a refresher on S/N, but I found the current discussion here as good or better!  Some of the best CN content I've seen. Thanks all and well done.

 

Question  -  How does the ASI1600  glow intensity compare to other popular sensors?  Is the issue unusually bad for this particular sensor? I know the earlier Canon DSLR's had some nasty glow issues.

 

It seems to be about as bad as my 5D III with long exposures. The 5D III has a bubble to the right, and increasing glow that spreads around the frame from the lower right corner. With 10-12 minute subs, it can get pretty bad. 

 

I know many Nikon DSLRs exhibit periphery glows, often brighter in one corner. The Canon 700D seems to exhibit a pretty bright bubble of a glow to the right center. 

 

I don't think the ASI1600 is particularly worse. I think that it's very low noise, and even lower dark current when cooled, make the glows a bit more obvious, as with DSLRs they can be hidden a bit under more random noise.

 

It should not be a problem for LRGB imaging at all.

 

I do think that the intensity of the glows with longer subs is a bit of a problem for narrow band imaging. They can be calibrated out as Syscore says...but in 600s and longer subs, there is a visible increase in noise in the areas of glow. 



#78 TimN

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Posted 18 June 2016 - 09:06 AM

I know my Nikon D5100 DSLR has some periphery glow with long exposures. Even if you don't calibrate it out - it is easily masked and removed in post processing. Since it only involves the periphery any extra noise is usually not noticeable. Minor cropping, if you have to get rid of the stacking artifacts, will also help. Jon, looking at your 10 minute sub the glow seems to be just around the edges, as well. I wonder, when calibrated out if the noise difference would even be noticeable. However, I assume if the exposure was increased so that the glow spread across more of the frame, that would be a problem. Of course, with this sensor we don't have to have really long subs. However, the 10 minute ones could be ok. Now, I'm away from home and using a tablet so maybe I can't see it well enough. :)

So, while the math may indicate a problem at 10 minutes maybe its not noticeable enough to matter.

Edited by TimN, 18 June 2016 - 09:07 AM.


#79 ncwolfie

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Posted 29 March 2017 - 02:51 PM

After reading through this thread, I understand that dark scaling should not be used with the 1600MM. So within the Pixinsight BPP script would I leave "optimize dark frames" checked or uncheck it?

Just a little confused on the terminology on the info popup menu on that part of the script.

 

Thanks,

Randy



#80 Peter in Reno

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Posted 29 March 2017 - 03:24 PM

ASI1600 shows some AMP glows which is why dark scaling should not be used. Yes, leave "optimize dark frames" unchecked.

 

Peter




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