8 replies to this topic

[adastranova]

Hello all:

 

Looking for tips on what I could be doing wrong with a fairly new ASI294MM camera. I had several successful sessions imaging galaxies but hit a snag when trying narrowband for the first time. I tried the Owl Nebula as a simple target for experimenting with camera settings.

 

My Ha and OIII flats and lights seemed to turn out normal. I am using 3X3 binning, -10C, Unity gain settings of 120 and Offset 30. Camera is on a C925Edge with 0.7X FR. The problem occurs when trying to use my 12 nm Astronomik SII filter. My lights were 180s long, and flats were taken with my standard light panel I have been using for years now. The SII filter has worked with other mono cameras I have used in the past. 

 

The individual light frames, 30K (8.78s) and 10K (2.34s) flat frames, and final flat master all show a very bright circular but diffuse disc in the frame center. Please see pics. Then when I go to calibrate and stack the final SII master light, there is a dark disc in the center. I have tried PixInsight WBPP 2.0 and also manually calibrating everything but the result is the same.

 

Any ideas? Haven't seen this issue before but I think it is with the camera or the camera settings. I should mention I have the latest ZWO drivers, so the cam has been unbinned from 4.63 to 2.3 microns. I am using 3x3 binning to get 0.87 arcsec/pixel for the 1645 mm FL.

 

Thanks much,

 

John

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Edited by adastranova, 07 April 2021 - 12:34 AM.

[Marcelofig]

It's not the filters or camera settings, it's the sensor itself. The Sony IMX492 sensor has these strange patterns, the weirdest thing is that they are only present in Ha and Sii and even weirder is that it is random (it would be different for each sensor). 

Check out this early review from last year. And if you check this site there is a lot of info about it.

 

https://www.macobser...94mm-pro-camera

https://www.cloudyni...mage-and-flats/

 

The good news is that proper calibration eliminates them completely. I generate the masters manually and then use these in PI's WBPP and it works perfect.

 

(I use flats darks to calibrate the flats and darks. And default binning of 2x2)

[ZL4PLM]

it has nothing to do with the sensor... zilch!

 

The disc is some kind of reflection artifact of the primary/secondary mirrors along with a few dust bunnies!

 

You will need to talk to someone who runs an SCT on the best way to take flats for them - but I with that disc showing the mirrors to strongly then you will struggle as it should be more uniform. 

 

You can prove it - run process the image without flats - there won't be the same dark disc.

 

what the 2 links posted below your post show something very different to what you are struggling with 

 

anyone own an SCT can advise how to remove that central mirror reflection - maybe a matt sheet over the panel to dull down reflections?

 

cheers

Simon

[adastranova]

It's not the filters or camera settings, it's the sensor itself. The Sony IMX492 sensor has these strange patterns, the weirdest thing is that they are only present in Ha and Sii and even weirder is that it is random (it would be different for each sensor). 

Check out this early review from last year. And if you check this site there is a lot of info about it.

 

https://www.macobser...94mm-pro-camera

https://www.cloudyni...mage-and-flats/

 

The good news is that proper calibration eliminates them completely. I generate the masters manually and then use these in PI's WBPP and it works perfect.

 

(I use flats darks to calibrate the flats and darks. And default binning of 2x2)

Thanks Marcel,

 

I see I am not the only one with these issues. There must be something in calibration I am not doing right. Glad you have been able to make the final images work. I need to use 3x3 for my focal length or I am oversampled at 2x2 and the HFR never gets below 5 or 6. Still would like to know how one filter is OK and another has a bright center. Someone else recommended I use 0 gain and 18 offset, which I am trying tonight. We'll see what the flats look like tomorrow!

 

Cheers!

[adastranova]

it has nothing to do with the sensor... zilch!

 

The disc is some kind of reflection artifact of the primary/secondary mirrors along with a few dust bunnies!

 

You will need to talk to someone who runs an SCT on the best way to take flats for them - but I with that disc showing the mirrors to strongly then you will struggle as it should be more uniform. 

 

You can prove it - run process the image without flats - there won't be the same dark disc.

 

what the 2 links posted below your post show something very different to what you are struggling with 

 

anyone own an SCT can advise how to remove that central mirror reflection - maybe a matt sheet over the panel to dull down reflections?

 

cheers

Simon

Thanks Simon, but I don't think so. I have been using this scope for over 3 years with 4 other cameras and have never seen this before. My flat panel is a tracing pad covered with a sheet of white acrylic and has worked very well. The 294MM does not perform like any other cam. If this is major improvement over the ASI1600MM, I have yet to see it. Changing the gain is my next step, as mentioned above. A useful outcome appears to be walking a fine line of variables but I do not yet know the path.

 

Best Regards,

 

John

[stryker66]

Thanks Simon, but I don't think so. I have been using this scope for over 3 years with 4 other cameras and have never seen this before. My flat panel is a tracing pad covered with a sheet of white acrylic and has worked very well. The 294MM does not perform like any other cam. If this is major improvement over the ASI1600MM, I have yet to see it. Changing the gain is my next step, as mentioned above. A useful outcome appears to be walking a fine line of variables but I do not yet know the path.

 

Best Regards,

 

John

I agree with Simon.. Check my post here.
https://www.cloudyni...mage-and-flats/

[adastranova]

I agree with Simon.. Check my post here.
https://www.cloudyni...mage-and-flats/

Thanks for the feedback guys. Yesterday my supplier agreed to take back the camera. I assume it's heading back to ZWO for their analysis. I am upgrading to the ASI2600MM-P.

 

Clear skies:)

[Rasfahan]

I‘ve had a lot of reflection and light leak issues with my QHY294M uncovered that were not visible with my other cameras (Panasonic, IMX183, IMX571 and ICX694 sensors). Calibration of the IMX492 data needs to be done extremely carefully. All in all I like the ASI2600MM much better. Since you do not need the small pixels of the 294M on the SCT, I am sure you will, too.

[adastranova]

I‘ve had a lot of reflection and light leak issues with my QHY294M uncovered that were not visible with my other cameras (Panasonic, IMX183, IMX571 and ICX694 sensors). Calibration of the IMX492 data needs to be done extremely carefully. All in all I like the ASI2600MM much better. Since you do not need the small pixels of the 294M on the SCT, I am sure you will, too.

 

Thanks Rasfahan,

 

I went with the 294MM first trying to avoid buying a larger filter set, but that was inevitable anyway. Looking forward to the 2600MM. ZWO makes some good cameras but I think the 2600 will provide a better starting point for processing.