m106

[mmnb]

C14 Edge HD + Hyperstar + EOS 60Da

Standard preprocessing up to deconvolution, masked stretch then HDRMT (masked to galaxies) and some saturation and curve nudging.  There is a line that shows up in the bottom 6th in all my frames, not sure what the cause is there; I might try and kicking it out in cosmetic correction.   Is collimation/focus error obvious here in the cropped frame (I can see the chromatic aberration in the stars when working on the image)?  I'm trying figure out to get it fixed, right now it seems that the error is position dependent.

EDIT: Link to xsif, linear image processed upto PCC:
https://drive.google.com/open?id=16cdndGEv2eXvJTQmWNv3IUyDG7omTZlZ

[bulrichl]

It is difficult to detect in the image that you posted. I guess it is dark banding?

If so you will not be able to remove it by CosmeticCorrection.

Explanation: Dark banding is caused by Canon's in-camera preprocessing. The sensor has an optically black area above and left of the actual image data. In my Canon EOS 600D (IIRC in this camera the same sensor is used as in the 60D), the normal image region is width=5202 and height=3465 pixels. The optically black area is 51 pixels above and 142 pixels left of the normal image region. Saturated hot pixels in the left optical black area cause dark banding over the whole width of the image (optically black region + image region). In y-direction these bands are a few pixels wider than the artifact.

You can inspect the optically black area: Enable temporarily the 'No image crop' option in 'Raw Format Preferences' and take a look at the y-region where the banding occurs in the left optically black area.

Actually this sort of banding is removed by a correct image calibration because all sorts of images (light, bias, dark, flat frames) ar affected. If you calibrated the lights with the option 'Optimize', this will be the cause that the banding is not removed totally. In this case try to use matched dark frames, and no bias frames for the calibration.

You can also try the CanonBandingReduction script. If these suggestions don't work, please report again.

Bernd

[dld]

Hello,

The CanonBandingReduction Script with the default settings and the "Protect from Highlights" tick box enabled, seems to fix the issue well. If you have similar issues regularly you may need to revise your calibration workflow as Bernd suggested earlier.

[wvanreeven]

Another way to prevent Canon banding is to use dithering during imaging. Unfortunately that will not fix the issue with the image that you posted.


HTH, Wouter

[mmnb]

Indeed, this was something like 30x30s exposures with dithering.  Thanks for all the cannon specific advice.

EDIT: Should add that calibration is done without darks due to the way cannon works with 'dark suppression'.

[bulrichl]

EDIT: Should add that calibration is done without darks due to the way cannon works with 'dark suppression'.

This seems to be a huge misunderstanding. Calibration with MasterDark and MasterFlat is needed at any rate!

See this guide: https://pixinsight.com/forum/index.php?topic=11968

Bernd

[mmnb]

To be sure, this is my current pre processing after noticing the dark current is suppressed in the Canon EOS 60Da:

Biases/Flats saved in 'RAW Monochrome' readout setting in maximDL.

Creation of master bias (using super bias).

In batch preprocessing (IIRC it won't run if you try using flats without bias or dark), supply the flats (not as master) and master bias with the lights and debayer here as well.

I believe this should be fine no (no dark frames, but biases needed to divide by flat)? This correction seems ok by eye.

[bulrichl]

If you refuse to read my guide I cannot help you. As I wrote above I used a Canon 600D (IIRC same sensor as in the 60D). You definitely need a MasterDark in order to properly calibrate the light frames of your camera.

Bernd

[mmnb]

No need to take offense. I've tried understanding appropriate handling for these Canon cameras and a few credible sources suggest not bothering with darks.

https://www.cloudynights.com/topic/664353-eos-60da-dark-and-bias-frames/?fromsearch=1

EDIT:
Just to put the main conflicting source inline:

http://www.nightanddayastrophotography.com/gallery/urbanm27nodarks.html
"This, along with the dark current suppression built into the hardware, removes the need for dark frames."


I have no doubt your guide describes the *correct* way to handle dark frames for calibration, but it isn't clear to me that they are *needed*. What I am trying to reconcile across sources is "is the effect of dark frame calibration clear and visible?". I don't see the answer to that in your guide, perhaps I have missed it.

[bulrichl]

I have no doubt your guide describes the *correct* way to handle dark frames for calibration, but it isn't clear to me that they are *needed*. What I am trying to reconcile across sources is "is the effect of dark frame calibration clear and visible?". I don't see the answer to that in your guide, perhaps I have missed it.

Yes, obviously you missed it. In my reply #1 I told you that a correct image calibration will remove this banding. I also explained the cause of the banding and described how you can inspect the subframes.

Perhaps you want to try these suggestions and communicate the results? You will not get things straight in a debate on principles.

Bernd

[mmnb]

I certainly will try your suggestions when I get the chance but it will be a few weeks.
Cheers!