Color Cast on all integrated files

Paul Abbott

I recently started using PI, following FastTrack including WPBB followed by Star Alignment and ImageIntegration. All my integrated images have the same left sided color cast. I thought there was a problem with my sensor but was assured that the camera is normal (QHY600C). At first I assumed a light leak but the cast occurs with Darks obtained with the camera alone. I have redone all my Flats, Dark Flats and Darks but the problem persists. 

Would be happy to provide raw data but not sure how to do that.

Thanks so much

Paul

BlockHead

OK. Good observations so far.

When you take your darks..... *is it dark?*

Also, integrated dark frames should be grayscale images. It doesn't make sense to see a color image of a dark frame (at least not in PixInsight).

OK...if you make your data available to download from a cloud drive I can look.

-the Blockhead

Paul Abbott

Thanks so much! And thank you for all your hard work producing the videos. They are the most well designed I have seen!

The files are about 123MB each. 

Let me know if there is a problem uploading from dropbox.

https://www.dropbox.com/sh/eleb9z94nnmho3a/AACnjr992IzqTvB7xKzeRXB0a?dl=0

BlockHead

Paul,

Was it dark when you took your darks. Was it daytime..in a lighted room... a computer monitor nearby?

-the Blockhead

BlockHead

Paul... another thing... and this one is kinda lame...

I processed your M101 data...which is what you have linked above. 

And it works perfectly ... no gradients... no problems FastTrack is in good standing.

However... you image above is a globular cluster. So that data is different in some way.

In addition..I would say that your Flats are overexposed. They read 0.9.  You really want values between 0.3 and 0.7 .

-the Blockhead

BlockHead

I have a little more information on something I found.

Some cameras, potentially like your model, do not behave well will very short exposures. 

This is from Bernd's Calibration Guide:

"Please note: The bias frames of cameras with a Panasonic MN 34230 sensor (e.g. ZWO ASI1600, QHY163 or
Atik Horizon) show a varying gradient across the frame and an inconsistent bias level when exposure times
< 0.2 s are used [4]. With such a camera, it is not advisable to use bias frames at all. However, it is not valid
to generalize this recommendation for all CMOS sensors: other CMOS sensors usually don't show this
anomaly of an inconsistent bias level. The only other exception that I am aware of is the Sony IMX294
sensor."

This means you might want to consider matching all flats and lights with matching dark frames AND make certain that the flats are longer than 2 seconds. 

But again, your M101 went together perfectly with no issues like you present.

-the Blockhead

Paul Abbott

Adam,

 The Darks were taken in the dark (at night). Yes I included a picture M13 as well M101 because I wanted to show that I have experienced this coloration on multiple targets and that this wasn't just a one off with this data. There was no M13 data mixed in. 

I am embarrassed to say that I think that I debayered the lights before using WPBB. I followed your advice from FastTrack to start over and everything looked good as you found.  I don't know if I am using my imagination but I think that I see some gradient in the integration file but it does not seem to be there after DBE.

My sensor is a Sony IMX455 and I have heard that bias frames may be problematic with the short exposures but was not sure what the minimum exposure should be with flats. I have played with varying the exposures but none of them are longer that two seconds. Since I did not know if my camera was a "badly behaving" camera or not, I followed your suggestion to use FlatDarks.

I can't tell you how helpful it is to have you confirm that the data is OK so I can eliminate hardware issues. I am really enjoying your videos, your teaching technique and philosophy. All of this is invaluable. Thank you!

Paul

I will reshoot my Flats with a lower brightness with my Flat Man. I set it for 50% ADU.

Thanks so much for

BlockHead

Yes... and if you can get a 2 second exposure... you might be able to avoid some other common pitfalls!

Thank you for following up. I really thought *I* had done something wrong since the results I got on my end looked good... because I could not reproduce your bad results..I kept at it for a while. lol

-the Blockhead