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ASI294 question

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#1 wargrafix

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Posted 05 October 2018 - 12:20 PM

While I am waiting for ZWO to return from vacation, I am wondering...is the dark calibration issue resolved?



#2 jgraham

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Posted 05 October 2018 - 02:46 PM

Good question. Some of us have never experienced a problem calibrating images taken with the ASI294MC Pro. I own a pair of 294s and I have never had a problem.

#3 wargrafix

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Posted 05 October 2018 - 04:46 PM

Sweet! Fist time I will be shooting with a cooled camera. I normally shoot with a 224mc. What did you first notice?

#4 jgraham

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Posted 05 October 2018 - 07:14 PM

That's an interesting question. The first thing that I noticed about the camera is its size and weight; smaller and lighter than the ASI071MC Pro. Its performance compared very well with its larger sibling and the TEC seems to work a bit better. Image-wise I was immediately impressed with the low noise, color, and resolution. It takes a while to notice the deep wells, but it gives the camera a wonderful dynamic range. That combined with the 14 bit ADC permits some very nice processing options. I haven't had any problems with the slightly smaller chip (4/3" versus APS-c), I just find myself not cropping off the edges nearly as much as I did with the larger camera. The ASI294MC Pro has become my workhorse camera, with my ASI071MC Pro being used more with my larger scopes that can take advantage of its larger chip. The 4/3" format of the ASI294MC Pro is also a good match for 1.25" filters like the OPT Triad. There is a region of amp glow in the upper right corner, but I never see it after applying darks. I feel that the 294 is a nice in-between format camera; not too big, and not too small.


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#5 Jon Rista

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Posted 05 October 2018 - 09:18 PM

While I am waiting for ZWO to return from vacation, I am wondering...is the dark calibration issue resolved?


Based on previous research into the issue, as well as ZWO's comments on it, I do not believe it is capable of being resolved. If the available packages the sensor comes in are the only available packages, then it is simply the design of the sensor package that limits how well and how completely the sensor can be cooled.

I think some people just push their data to greater extremes than others, which is why you get differences of opinion on how much the issue matters. Some people may also be more capable of getting very deep exposures that bury the background signal issues a bit more in more pleasing skyglow as well.

In any case, no I do not believe the issue has been resolved, nor do I believe it even can be resolved.
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#6 wargrafix

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Posted 06 October 2018 - 06:47 AM

Hmmm.

 

 

 

 

I try not too overstretch my data but I have been looking at doing longer iteration times. Auto guiding has been the easiest part of this journey.  I am on a Mexican standoff.  Buy it...skip it...wait for a v2 294 pro...or another camera on the horizon. 

 

The first more or less will be fine

Skip may avoid the issue,  but there are no competition cameras like it at the price point. ..is there?

Nothing has been announced about a v2.

nothing is announced about a new camera to come.

 

 

 

Hmmmmmm



#7 jgraham

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Posted 06 October 2018 - 09:58 AM

The funny thing about technology... it never hurts to wait. Shop around and get what you want for a price you are comfortable with.

 

Have fun!



#8 mvas

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Posted 06 October 2018 - 11:51 AM

Based on previous research into the issue, as well as ZWO's comments on it, I do not believe it is capable of being resolved. If the available packages the sensor comes in are the only available packages, then it is simply the design of the sensor package that limits how well and how completely the sensor can be cooled.

I think some people just push their data to greater extremes than others, which is why you get differences of opinion on how much the issue matters. Some people may also be more capable of getting very deep exposures that bury the background signal issues a bit more in more pleasing skyglow as well.

In any case, no I do not believe the issue has been resolved, nor do I believe it even can be resolved.

According to Chad & Sean of ZWO, there was a driver update for the ASI-294 on Aug 21, 2018

They state, "The latest updated driver did address the Dark Current issue".

Was your research performed, before or after, this latest driver update?


Edited by mvas, 06 October 2018 - 11:54 AM.


#9 bulrichl

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Posted 07 October 2018 - 04:23 AM

According to Chad & Sean of ZWO, there was a driver update for the ASI-294 on Aug 21, 2018

They state, "The latest updated driver did address the Dark Current issue".

Was your research performed, before or after, this latest driver update?

I am not Jon, but did some investigations on the ASI294.

 

When I bought my ASI294 (in January 2018), the current ASCOM driver was v1.0.3.12. I determined gain (at gain 120), read noise and dark current rates in a temperature range of -15 ... +10 °C with this driver version. Method: Berry, Burnell: Handbook of Astronomical Image Processing, chapter 8.2, "Basic CCD Testing". This chapter is available in the internet as error-corrected version: Errata to 1st Printing 2nd Edition of HAIP.pdf .

 

I was amazed that the dark current rates that I obtained were significantly lower than those published by ZWO at that time. Especially, the plot of logarithmized dark current values vs. temperature did not show the strongly curved shape, but nearly a straight line was obtained (as one would expect). Later on, ZWO published revised dark current rates for the ASI294 which were somewhat lower than the previously published data. Even these values exceeded the dark current rates that I measured significantly.

 

I have done my measurements repeatedly and the results are reproducible. After udpdating to v1.0.3.18 and later to v1.0.3.21 I got the same dark current rates as with v1.0.3.12. So I conclude that ZWO's method of determining the dark current rates is incorrect.

 

However, these results have nothing to do with the colored background artifact. There is no such artifact in the dark frames nor in the MasterDark.

In the ZWO forum you can read the manufacturer's statements regarding this issue: [ASI294] Background artifact issue .

 

Bernd



#10 wargrafix

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Posted 07 October 2018 - 07:54 AM

Wow...this is really tough.

I was hoping to do frames with at least 240 seconds each

#11 jgraham

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Posted 07 October 2018 - 10:15 AM

My standard sub is 240 seconds, gain 200, 0C. I could easily go longer, but this takes me to my skyglow limit of magnitude 18ish and there is no point in imagining more skyglow.

#12 wargrafix

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Posted 07 October 2018 - 11:48 AM

Ah! Please excuse my nervousness. First time buying an expensive camera

#13 Zebenelgenubi

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Posted 07 October 2018 - 01:47 PM

I am not Jon, but did some investigations on the ASI294.

 

When I bought my ASI294 (in January 2018), the current ASCOM driver was v1.0.3.12. I determined gain (at gain 120), read noise and dark current rates in a temperature range of -15 ... +10 °C with this driver version. Method: Berry, Burnell: Handbook of Astronomical Image Processing, chapter 8.2, "Basic CCD Testing". This chapter is available in the internet as error-corrected version: Errata to 1st Printing 2nd Edition of HAIP.pdf .

 

I was amazed that the dark current rates that I obtained were significantly lower than those published by ZWO at that time. Especially, the plot of logarithmized dark current values vs. temperature did not show the strongly curved shape, but nearly a straight line was obtained (as one would expect). Later on, ZWO published revised dark current rates for the ASI294 which were somewhat lower than the previously published data. Even these values exceeded the dark current rates that I measured significantly.

 

I have done my measurements repeatedly and the results are reproducible. After udpdating to v1.0.3.18 and later to v1.0.3.21 I got the same dark current rates as with v1.0.3.12. So I conclude that ZWO's method of determining the dark current rates is incorrect.

 

However, these results have nothing to do with the colored background artifact. There is no such artifact in the dark frames nor in the MasterDark.

In the ZWO forum you can read the manufacturer's statements regarding this issue: [ASI294] Background artifact issue .

 

Bernd

I routinely image using 200 to 500 second subframe exposures with my ZWOASI294mc_Pro.  I have never had a case in which amp glow or background color could not be calibrated out using standard processing techniques.  I am baffled by the some of the observations posted above.  Can someone suggest a sensor defect which can cause artifacts in light frames but allows the dark frames to be artifact free?



#14 jgraham

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Posted 07 October 2018 - 03:31 PM

There's no need to be in a hurry. Plan-B might be having your 550D modified. I had Gary Honis do a Baader modification to my 550D and that added several years to its useful life. I still have it as a backup camera.



#15 Jon Rista

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Posted 07 October 2018 - 03:42 PM

According to Chad & Sean of ZWO, there was a driver update for the ASI-294 on Aug 21, 2018

They state, "The latest updated driver did address the Dark Current issue".

Was your research performed, before or after, this latest driver update?

I am aware the driver was updated. I don't believe that would necessarily have any bearing on the fundamental issue, which is that the bare area on the back of the sensor package where a TEC could contact it is smaller than the sensor area itself. The rest of the back of the sensor package has the contact array. Some have said the issue was due to flats, however I am not entirely convinced of that...I DO believe that flats can cause similar issues, but in the examples demonstrated in the following thread, the issue seems to be dark current related:

 

https://www.cloudyni...-pro/?p=8605322

 

This does seem to be a YMMV problem. Some people don't seem to experience it, others have a much bigger problem with it. It may depend on how you stretch, and shallow stretchers may not experience issues while deep stretchers very well could. The issue is a form of FPN, and one of a very large scale, so dithering and deep integrations won't improve it (in fact, likely worsen it.)


Edited by Jon Rista, 07 October 2018 - 03:52 PM.


#16 wargrafix

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Posted 07 October 2018 - 04:35 PM

I use my 550d for birding. Also, the results compared to my 224 is night and day.

What are the competitive products at this price point?

#17 AhBok

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Posted 07 October 2018 - 06:33 PM

I worked with Sean at ZWO on my 294 for a few months sending exposures, darks, etc., and trying various exposures and temps for flats, darks and lights. I got some pretty pictures, but only because I had to darken the background to the point where I was clipping data. Funny, but I got a lot of compliments on my black sky, but I knew I was losing detail. In the end, Sean agreed that I would never be able to achieve the dynamic range that was advertised for that camera. I used 200 gain or more with short exposures for best results, but wanted to use longer exposures with unity gain or less. ZWO kindly let me return my camera under warranty. I purchased an ASI071MC Pro and am completely happy with its performance. I do believe my 294 would have made an awesome EAA cam, but that is not my current interest.

#18 bulrichl

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Posted 08 October 2018 - 03:55 AM

I got some pretty pictures, but only because I had to darken the background to the point where I was clipping data. Funny, but I got a lot of compliments on my black sky, but I knew I was losing detail.

This is exactly what I experienced at gain 120 and exposure times of 150 and 300 s.

 

I used 200 gain or more with short exposures for best results, but wanted to use longer exposures with unity gain or less.

I will try gain > 120 with shorter exposure time as a last attempt. If that doesn't work for me, I'll also purchase a different camera.

 

Bernd



#19 glend

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Posted 08 October 2018 - 06:46 AM

Driver updates are no fix for the poor cooling solution used on the 294 (The chip cannot be evenly back cooled due to its design). I agree with Jon R, and he should know as he Beta tested the camera. There are better ASI choices that are easy to calibrate. The 294 is being marketed now by ZWO as a EAA camera, that should tell you enough, deep well depth is meaningless if it can't be used for longer sub imaging.


Edited by glend, 08 October 2018 - 06:47 AM.


#20 bulrichl

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Posted 08 October 2018 - 08:15 AM

Driver updates are no fix for the poor cooling solution used on the 294 (The chip cannot be evenly back cooled due to its design). I agree with Jon R, and he should know as he Beta tested the camera. There are better ASI choices that are easy to calibrate. The 294 is being marketed now by ZWO as a EAA camera, that should tell you enough, deep well depth is meaningless if it can't be used for longer sub imaging.

It is not true that the camera is marketed now by ZWO as a EAA camera. Show me one hint in the description or in the manual of the camera which would tell that it is not well suited for long exposure deep sky astrophotography - that exists only in your imagination.

 

It is not proved at all that the cooling system is causing the background artifact. How could uneven cooling affect the red, green and blue pixels in a different way and generate a fixed pattern? In the thread on ZWO's forum, [ASI294] Background artifact issue , the last answer from ZWO to the question "Wasn't this issue related to the tec cooler?" was: "Not cooling". Thus nobody has explained this behavior so far, and I guess you can't either.

 

Bernd


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#21 mvas

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Posted 08 October 2018 - 08:38 AM

Driver updates are no fix for the poor cooling solution used on the 294 (The chip cannot be evenly back cooled due to its design). I agree with Jon R, and he should know as he Beta tested the camera. There are better ASI choices that are easy to calibrate. The 294 is being marketed now by ZWO as a EAA camera, that should tell you enough, deep well depth is meaningless if it can't be used for longer sub imaging.

Per ZWO, they can make changes to the driver, which allows them to shutdown circuitry that was generating heat unnecessarily.

Beta Tester - and that is why I asked Jon if he re-tested with latest driver.

 

You say, "... The chip cannot be evenly back cooled due to its design ..."

If you know this to be true, then give us the min / max temperature difference across the chip?

And does the temperature gradient highly correlate to the background artifact or not?

If you cannot, then what is it that you actually know?


Edited by mvas, 08 October 2018 - 09:16 AM.

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#22 wargrafix

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Posted 08 October 2018 - 08:38 AM

I think he is referring to their emphasis on its EAA capabilities. I noticed this. I am the one who asked that question. He answered but with zero elaboration.

 

I am not dumping on ZWO, but if I am spending money, I want to know I am not buying cat in bag.

 

I live in the tropics and 28-32 degrees are common.



#23 wargrafix

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Posted 08 October 2018 - 08:39 AM

Per ZWO, they can make changes to the driver, which allows them to shutdown circuitry that was generating heat unnecessarily.

Did that driver fix the issue?



#24 Zebenelgenubi

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Posted 08 October 2018 - 08:39 AM

It is not true that the camera is marketed now by ZWO as a EAA camera. Show me one hint in the description or in the manual of the camera which would tell that it is not well suited for long exposure deep sky astrophotography - that exists only in your imagination.

 

It is not proved at all that the cooling system is causing the background artifact. How could uneven cooling affect the red, green and blue pixels in a different way and generate a fixed pattern? In the thread on ZWO's forum, [ASI294] Background artifact issue , the last answer from ZWO to the question "Wasn't this issue related to the tec cooler?" was: "Not cooling". Thus nobody has explained this behavior so far, and I guess you can't either.

 

Bernd

I also think that the cooling issue is a red herring.  I have worked with semiconductor devices for the past 30 years.  A CMOS sensor is integrate onto a Si crystalline substrate.  Si has a very high coefficient of thermal conductivity which facilitates the flow of heat across the device.  Unless there is a large thermal hot spot on the sensor, then it is all but impossible to get a substantial temperature gradient across the device.  The power dissipation in the sensor is pretty small so that even if the sensor was only edge cooled by the TEC you wouldn't see much of a temperature difference across the chip.  Here is a question our northern forum members can answer in a month or so.  Does turning off the cooling remove the artifacts?



#25 mvas

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Posted 08 October 2018 - 08:53 AM

I am aware the driver was updated. I don't believe that would necessarily have any bearing on the fundamental issue, which is that the bare area on the back of the sensor package where a TEC could contact it is smaller than the sensor area itself. The rest of the back of the sensor package has the contact array. Some have said the issue was due to flats, however I am not entirely convinced of that...I DO believe that flats can cause similar issues, but in the examples demonstrated in the following thread, the issue seems to be dark current related:

 

https://www.cloudyni...-pro/?p=8605322

 

This does seem to be a YMMV problem. Some people don't seem to experience it, others have a much bigger problem with it. It may depend on how you stretch, and shallow stretchers may not experience issues while deep stretchers very well could. The issue is a form of FPN, and one of a very large scale, so dithering and deep integrations won't improve it (in fact, likely worsen it.)

I cannot find the message now, but I will search and post a link ...

 

One person stated ...

"... With the TEC ON - I do see the background artifact ..."

"... With the TEC OFF - I do not see the background artifact ..."

 

We do not know if the above applies to every unit with the background artifact issue or not.

If it is a TEC cooling issue - Would the background artifact be 100% eliminated when the TEC is OFF?

The problem should become worse, as the TEC power is increased.

This should be provable, if it is TEC related or not.

 

I don't know if they were using the old driver or new driver, or the Ambient Temperature vs the Delta TEC temperature

 

The most recent  Dark Current Graph is now considerably lower vs the original Dark Current Graph


Edited by mvas, 08 October 2018 - 09:02 AM.



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