Background artifact issue

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Creeping_Death
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Background artifact issue

Post by Creeping_Death » Mon May 21, 2018 10:32 am

Dear ZWO team,
I am experiencing issues with my new ASI294. I have a strange pattern in the background of all my integrated/stacked pictures. The more exposures I stack, the more clear the artifact. I looks like a rectangle and creates a different color pattern between the center of the image and the outer region (please see pictures attached).

A similar behavior is already described by a user in this thread on Cloudynights: https://www.cloudynights.com/topic/6110 ... wo-asi294/
In this thread, the user says he already contacted Sam from ZWO and that he got the response that the size of the peltier cooling element, which is smaller than the sensor, causes this behavior due to different chip temperatures in the middle and outer region of the sensor.

My imaging settings are: ASI294, Firmware 1.0.1.7, Gain 121, Sub-exposures 300s, Cooling -10°, Binning 1x1, Capture software SGP, all frames calibrated with Dark+Flat+Bias and then stacked in Pixinsight.

Do you have any updates on this, can you provide support how to fix this issue?

Kind regards,
Jan
Attachments
Markarians.jpg
Example 2
M97.jpg
Example 1

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Sam
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Re: Background artifact issue

Post by Sam » Thu May 24, 2018 1:58 am

Hi Jan
from our experience, this is because the dark current of 294 is a little higher and cannot be controlled very well during very long exposure
CMOS is not a simple sensor IC like CCD, it integrated many other digital parts such as power IC, gain amplifier etc, so the dark current is hard to control as stable as CCD.

I suggest you can shorten the exposure and try again
from Andy's response the result is better
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Creeping_Death
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Re: Background artifact issue

Post by Creeping_Death » Fri May 25, 2018 8:33 pm

Dear Sam,

thank you for your reply. I already tried to reduce the exposure time to 120s per Subexposure as it was suggested by Andy in the thread. However, this reduction did not help unfortunately, as the artifact in the background is still the same. Attached you find a stack of 20x120s exposures of the same object.

To be honest, I must say if 120s exposures are not possible then the use of this camera for traditional deepsky photography is very limited for me.

Best regards,
Jan
Attachments
M97_120sx20.jpg

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Sean.Wang
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Re: Background artifact issue

Post by Sean.Wang » Sun May 27, 2018 2:10 am

still need to take calibrate frames.
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Creeping_Death
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Re: Background artifact issue

Post by Creeping_Death » Mon May 28, 2018 8:06 am

Dear Sam,

That is clear, the 120s stack shown above is fully calibrated with matching darks, flats and bias. Otherwise you would see vignetting and dark/amp glow.

Jan

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Sean.Wang
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Re: Background artifact issue

Post by Sean.Wang » Mon May 28, 2018 11:04 am

amp-glow is perfectly calibrated, I think dark frame is good. The problem should be the flat frames. Did you try this process?
Attachments
QQ截图20180528184856.jpg
ZWO | Marketing Consultant
Location:lon=120.6 lat=31.3
SuZhou China

motto:
Don't face one's fate, can't be a real man;
Don't know manners, can't be gentle;
Don't know meaning behind the words, can't understand man's heart.

bulrichl
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Location: La Palma (Canary Islands)

Re: Background artifact issue

Post by bulrichl » Tue May 29, 2018 12:34 pm

Hi Sam and Sean,

I am experiencing a similar colored background in the integrations of my ASI294MC Pro using a Takahashi FSQ 106N. This artifact is neither caused by light pollution nor is it IFN signal: I integrated 50 frames before meridian flip and 60 frames thereafter (no rotator was used). The problematic background was at the same sensor positions, which is evident in the appended images ("Image_1.JPG" and "Image_2.JPG", STF Autostretch applied in PixInisght).

Image
Image

Acquisition conditions: image acquisition (light frames as well as calibation frames [darks, flat-darks and flats]) with Sequence Generator Pro, exposure time 50 and 60 x 150 s respectively at gain 120, -15 °C, dithering applied. I did not use high cooling power: the set temperature was -15 °C at an ambient temperature of 14 - 12 °C, so the temperature difference was actually only 29 - 27 degrees. The cooling power was always below 50 %. I guess that the settings for the cooler have been well suited, and I don't like to go up with temperature because of thermal noise.

It's intruiging to me that this artifact is well reproducible: the light frames for Image_3.JPG (190 x 150 s at gain 120, -15 °C, dithering applied) were taken 1 month before. Compared with the 2 images above the pattern of the colored background artifact again appears at the same regions of the sensor.

Image

My workflow (in PixInsight): Image calibration with MasterDark and MasterFlat [Flats calibrated with MasterFlat-Dark], Debayer, Alignment, Integration).

The artifact definitely is not present in my MasterDark. The debayered MasterDark (same stretching applied as in the integration) shows 'amp glow', but not a trace of colored background is detectable in it. Furthermore, when I subtract the bias-offset from each light frame and then calibrate with MasterFlat, the same colored background with the same strength results after debayering, alignment and integration. So this artifact is only in the light frames.

I suspected that my MasterFlat, that was based on flat frames with low exposure time, was the culprit. So I made new flat frames with an exposure time of 3 s. Using this new MasterFlat for Image calibration, the resulting new integration was not distinguishable from the former one.

I transferred a zip archive of images to a filehoster and gave the link to ZWO, but unfortunately ZWO has not managed to download them due to file size.

At this point I don't know what to do next. The light frames of this camera do not seem to calibrate properly. I need your support and hope you are willing to help.


My ASI294MC Pro had the following Firmware versions:
FW version: V 5.0
FPGA FW version: 294 V 1.0.2.7

Bernd

bulrichl
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Location: La Palma (Canary Islands)

Re: Background artifact issue

Post by bulrichl » Tue May 29, 2018 12:42 pm

Hi again,

Here are the attachments (sorry for the inconvenience):

Image_1.JPG:
Image_1.JPG
Image_2.JPG:
Image_2.JPG

Image_3.JPG:
Image_3.JPG

Bernd

jmtanous
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Joined: Fri Jan 05, 2018 10:10 pm

Re: Background artifact issue

Post by jmtanous » Tue May 29, 2018 9:22 pm

Hi,

I am experiencing a similar situation with my ASI294 even with 60s lights.

I am calibrating my images with darks, dark-flats and flats and the integrated stack exhibit a residual pattern. I also own an ASI1600MMC-V3 that I use with the same optics (Takahashi FS60 and Epsilon 160) and the same calibration procedure works perfectly.

Please advise what to do?

Regards,

José

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Sean.Wang
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Re: Background artifact issue

Post by Sean.Wang » Thu May 31, 2018 11:48 am

jmtanous wrote:Hi,

I am experiencing a similar situation with my ASI294 even with 60s lights.

I am calibrating my images with darks, dark-flats and flats and the integrated stack exhibit a residual pattern. I also own an ASI1600MMC-V3 that I use with the same optics (Takahashi FS60 and Epsilon 160) and the same calibration procedure works perfectly.

Please advise what to do?

Regards,

José
Hi Jose
Thanks for telling us about your camera. We are doing some testing to improve the performance of 294pro. Most confused me is where does these artifacts come from. I can't see any special thing in dark frame. And flat frames also don't including that.
I was wandering if 10s lucky imaging would aviod that or not? maybe the exposure time will be the key of this problem. If we can find out the reason, we will be able to improve the performance.
ZWO | Marketing Consultant
Location:lon=120.6 lat=31.3
SuZhou China

motto:
Don't face one's fate, can't be a real man;
Don't know manners, can't be gentle;
Don't know meaning behind the words, can't understand man's heart.

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