Background artifact issue

creeping_death

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/611039-help-me-with-this-artifact-zwo-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

Sam@ZWO

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

creeping_death

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

Support@ZWO

still need to take calibrate frames.

creeping_death

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

Support@ZWO

amp-glow is perfectly calibrated, I think dark frame is good. The problem should be the flat frames. Did you try this process?

bulrichl

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).

Acquisition conditions: image acquisition (light frames as well as calibation frames ) 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.

My workflow (in PixInsight): Image calibration with MasterDark and MasterFlat , 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

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

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

Support@ZWO

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.

ahbok

Sam—Please add me to the list of users with this problem. I cannot use anything longer than 60 seconds and must use at least 199 gain in order to minimize the effect. I, too, use lights, darks, flats, and dark flats. I get this stacking in both DSS and APP. I really want to image this summer at a dark site using a gain setting with a larger DR. Please advise what we ASI294 are to do.

Randy Roy

Support@ZWO

Hi, Andy was the first user report this. I read his post, looks he use 2min exposure to reduce the artifact. Another guy use Sony A7 looks have same issue, he wrote a post too, I think he find some way in processing to reduce the issue.

https://www.cloudynights.com/topic/576265-sony-a7s-purplegreen-swathes/

jmtanous

Sean.Wang wrote:
Hi, Andy was the first user report this. I read his post, looks he use 2min exposure to reduce the artifact. Another guy use Sony A7 looks have same issue, he wrote a post too, I think he find some way in processing to reduce the issue.

https://www.cloudynights.com/topic/576265-sony-a7s-purplegreen-swathes/

Hi,

According to Mark, the guy who reported a similar issue with the Sony A7, he hasn't found a solution to this issue with the Sony A7. Probably the issue is not related at all but it looks similar to the one reported here.

https://www.cloudynights.com/topic/596025-zwo-asi294-mc-pro/?p=8623769

What Mark suggested is that the Sony A7 issue might be related to some onboard processing of the flats.

I will create a couple of master flats created with exposure times and I will try to calibrate them between each other. I will post my results, this might give us some ideas if the issue is similar to the one reported on Sony A7.

Cheers,

Jose

Support@ZWO

Thank you, I think issue of A7 is quite like 294, the phenomenon is nearly the same.

bulrichl

Hi Sean,

up to now there was not much help from ZWO in respect to the colored background artifact issue with the ASI294MC Pro. What I read from you was only guesswork so far.

Is ZWO even working on that problem currently? What are the findings then?

Bernd

vichman

Dear Sam,

Dear Sean,

I would also be very interested to hear about your own findings and your suggestion on how to deal with this.

So far I haven't experienced this observation with my ASI294 myself, but I would like to be prepared.

Thanks very much in advance.

Stefan

jmtanous

Hi,

These are some master flats created with different exposures times, 1s and 5s. A flatman screen with controllable brightness was used to for the capture. The histogram of the flats had 3 humps, the green hump was ending close to 30k ADU. The red and blue humps were close to 11k ADUs. The flats were calibrated using 64 darks of the same exposure time per set. The master flats were created by integrating 64 individual flat frames per set.

I am also attaching an uncalibrated 60s light frame. I calibrated it just using the master flats and it looks like the master flat overcorrects the light frame.

Feel free to download and play with the images. They were

Calibrated 5s master flat:

https://drive.google.com/open?id=17c0Zvu5H9c1zMfIkSld_Hd5xJKFJGBvl

Calibrated 1s master flat:

https://drive.google.com/open?id=1uk4DWdcyAPVt6V_1hA_jj7Y9oPretAES

Uncalibrated 60s raw light of M13

https://drive.google.com/open?id=18fEoGi_gxTYXfnW0lMl5mZQ5S6BUPHnr

I am also attaching the histogram of an individual flat frame and an integration of 88 x 1 min exposures. The images were dithered and calibrated with 128 x 1min darks and the master 5s flat frame. The image is heavily stretched to show the uneven background.

Cheers,

Jose

Support@ZWO

jmtanous wrote:
Hi,

These are some master flats created with different exposures times, 1s and 5s. A flatman screen with controllable brightness was used to for the capture. The histogram of the flats had 3 humps, the green hump was ending close to 30k ADU. The red and blue humps were close to 11k ADUs. The flats were calibrated using 64 darks of the same exposure time per set. The master flats were created by integrating 64 individual flat frames per set.

I am also attaching an uncalibrated 60s light frame. I calibrated it just using the master flats and it looks like the master flat overcorrects the light frame.

Feel free to download and play with the images. They were

Calibrated 5s master flat:

https://drive.google.com/open?id=17c0Zvu5H9c1zMfIkSld_Hd5xJKFJGBvl

Calibrated 1s master flat:

https://drive.google.com/open?id=1uk4DWdcyAPVt6V_1hA_jj7Y9oPretAES

Uncalibrated 60s raw light of M13

https://drive.google.com/open?id=18fEoGi_gxTYXfnW0lMl5mZQ5S6BUPHnr

I am also attaching the histogram of an individual flat frame and an integration of 88 x 1 min exposures. The images were dithered and calibrated with 128 x 1min darks and the master 5s flat frame. The image is heavily stretched to show the uneven background.

Cheers,

Jose

Thank you so much. We will keep working on this issue. We saw a post on CN said Sony A7 have same issue. that guy use some processing trick to get rid of it.

jmtanous

Thank you so much. We will keep working on this issue. We saw a post on CN said Sony A7 have same issue. that guy use some processing trick to get rid of it.

Do you want me to run any other test? The camera looks very sensitive and I am really looking forward to find a solution for this issue.

Cheers,

Jose

Support@ZWO

jmtanous wrote:

Thank you so much. We will keep working on this issue. We saw a post on CN said Sony A7 have same issue. that guy use some processing trick to get rid of it.

Do you want me to run any other test? The camera looks very sensitive and I am really looking forward to find a solution for this issue.

Cheers,

Jose

Oh, thank you! If anyone found some way maybe solve this problem, please tell us. You all very good at astro imaging, we'd like to hear your suggestions!

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