Zero or insignificant signal detected (empty image?) on processing DSLR flats

[dchamberlain]

Hello,

Hopefully someone can shed some light on this problem. I have taken a series of flat frames (30-50) from my Canon 6D Mark II and I am trying to create a master flat from them. The flat frames are all taken at 800 ISO, 1/1000 sec exposure and each one yields a histogram in dead center. Viewing them in Photoshop or Canon's Digital Image assistant shows the histogram in the center and the image displayed looks like a perfect flat.

I've calibrated these images with the master bias and master dark and the calibration runs without errors or warnings. The calibrated flats are .xisf files. When I take the calibrated flats through ImageIntegration however I get the message "Zero or insignificant signal detected (empty image?)" right off and the processing stops. If I open one of the calibrated flats in PixInSight, the images are black, even if I stretch them. Could something be going wrong in the calibration?

Help!

Thanks,

Dale

[pfile]

dont know if this is your problem, but the histogram in DPP/Photoshop is that of a default stretch. with a centered histogram in these programs you are actually very much underexposed. i used to use +2EV when i used a DSLR and that yielded a reasonable exposure in linear mode.

a 2nd possibility is that the bias and or darks could be wrong and so are indeed leaving 0 signal in the result. can you check the calibrated images and see what they look like?

rob

[dld]

1/1000 sec exposure time for flats is too short and may introduce other problems like shutter shadow. Some useful advice on how to take flats with a DSLR can be found here: http://www.myastroscience.com/proper-flats-with-dslr

[dchamberlain]

Thanks for your responses. When I look at the calibrated flats they look black, even when auto stretched. Nothing like the CR2 files. The information in your link dld is very helpful. I will try to get better flats using it. I did set the raw DSLR defaults in format explorer but I unchecked the setting "No image flip" because I was previously having geometry errors.

Hopefully your tutorial will be my answer!

[pfile]

good catch, i looked right past the 1/1000 - that is definitely too short for most light sources and yes you'll probably have shutter issues too.

rob

[dchamberlain]

Well I followed the tutorial, took 30 flats using aperture priority with +2 EV. Ran them through PixInSight calibration, and then to ImageIntegration. No joy. Same error message "Zero or insignificant signal detected (empty image). Most frustrating.

I'm beginning to think PixInSight is not handling CR2 files from a Canon 6DMKII.

Any suggestions?

[sharkmelley]

Yes it is very likely that DCRaw (used by PixInsight) does not handle 6D MkII files properly.  6D mkII is a new camera and DCraw stopped being updated a long time ago.

You could try the test version of LibRaw:
https://pixinsight.com/forum/index.php?topic=11726.0

Or else, please upload one of your CR2 flat files to Dropbox or Google Drive or similar.  We can then take a look at the actual raw file.  Those signal levels are much too low for a +2EV exposure.  Another possibility is to convert them to Adobe DNG format before opening in PixInsight.

Mark

[dchamberlain]

sharkmelley,

Thanks for your help! It is most definitely a problem with DCRaw not being able to handle the CR2 files from the Canon 6DMKII. I converted the CR2 files to DNG and the flats integration process worked like a charm!

Now with regard to LibRaw, how do you integrate it with PixInSight?

Thanks again,

Dale

[pfile]

the instructions are in this thread:

https://pixinsight.com/forum/index.php?topic=12126.0

rob

[sharkmelley]

Now with regard to LibRaw, how do you integrate it with PixInSight?

Sorry, I gave you the wrong link.  Try this one:

https://pixinsight.com/forum/index.php?topic=12126.0

Mark