DSLR Crosshatch pattern

[edarter]

Hi,

I posted a week or so ago about a possible DSLR problem, and the general consensus was that it was the result of either poor seeing or dew at the time. I've finally got some time to try and process the better images I took of the Orion nebula on that night but I'm now seeing another 'funny' which I'm not sure about. When I stack the images in DSS I'm getting a funny vertical / horizontal cross hatch pattern on the resulting image. I've attached one here, no processing done to it other than to reduce to 16 bit in order to save as JPG. Is this expected from a DSLR? I cannot recall having seen this before so I'm not sure if its a setting, whether there could be a rogue frame somewhere (be that image, dark or bias) or whether there is actually something going on with the sensor. Any help / advice greatly appreciated!

oh - also, I now I've not adjusted the levels but should the core fringes really show that purple? it almost looks blown out purple and I'm not sure how I would process that out.

Many thanks
Ed

[carastro]

That's normally down to the debayer pattern.  Did you pick choose the right model of DSLR in the stacking settings at the bottom left of DSS?

Carole 

Edited January 30, 2020 by carastro

[edarter]

just to add to this, have done an initial levels balance and the magenta is waaaay out of control! What have I done wrong??

[edarter]

Hi Carole,

I certainly haven't knowingly changed it, but will have a look now.

Thanks
Ed

[edarter]

8 minutes ago, carastro said:

That's normally down to the debayer pattern.  Did you pick choose the right model of DSLR in the stacking settings at the bottom left of DSS?

Carole 

Sorry Carole, do you mean in the RAW / FITS DDP setting section? I can't see anything about a specific DSLR type in there...

[carastro]

Yes in that box, if you tick the fits tab and tick mono (Yes makes no sense to me either), then you will get a drop down box where it says camera.  Choose your camera.  Mine was never shown, but I think if you have a Canon camera, the Bayer Matrix is probably the same for all of them, I used to just tick the closest one to mine which wasn't listed.

Carole 

[edarter]

just had another go at stacking and its made no difference  Could it be a setting in APT when I did the capture?

[carastro]

I don't have any more ideas, see what others think.

Carole

[almcl]

Is the cross hatch pattern present in your flats (assuming you took some) ?  

[wxsatuser]

Canon banding issue.

[alacant]

1 hour ago, carastro said:

if you tick the fits tab

 I think the OP may be using raw frames from a DSLR. 

17 minutes ago, wxsatuser said:

Canon banding issue.

If so try a stack of dark frames. No need to temperature match them. We talked about it here.

HTH

[almcl]

32 minutes ago, wxsatuser said:

Canon banding issue.

Is that likely with a 600?  I know it plagues the 750 and on but I thought the ones before didn't suffer from it (certainly my 700 has never exhibited it in 5 years and 33,000+ frames) 

[alacant]

49 minutes ago, almcl said:

my 700 has never exhibited it

Same here. I think the 600 has the same electronics and/or sensor.

Was a bias subtracted from the frames before stacking?

Maybe post a link to a few frames so we can try.

Cheers

Edited January 30, 2020 by alacant

[edarter]

Yes, stacking RAW images. I took darks and bias frames but no flats I'm afraid. It is an astro modded Eos600d but never noticed this before. Will the overly purple core fringe be another indicator? 

I will put some frames on Dropbox in a minute and share a link

[edarter]

Ok, there is a distinct possibility I may have been a complete numpty here. For some reason best known to my inner brain when I was VERY tired trying to stack these images I seemed to think they needed to be converted to TIFF beforehand, which I did. I have no explanation as to why I would have thought this as I've never done it before!!
I just tried a very brief stack of a subset of light RAW frames and the image seems a lot better. Now doing a proper stack of all the RAW frames...lights, darks and bias. Fingers crossed this is what the issue was!

Really sorry to have wasted everyones time though if it is!

[almcl]

No need to apologise! 

It's a learning process for all of us.  If you can take some flats, that will help with the vignetting that shows in the image at the top. 

Not sure about the colour, there seems to quite a lot of light pollution and dealing with this effectively is always a challenge, particularly with an astromodded  DSLR. What method are you using? 

[edarter]

Well that seems to have been the problem!! So there yo have it, needlessly converting to TIFF before running through DSS. I did a new stack of all the images and the sky is much darker now and the colours of the nebula much less over exaggerated, so knowing that I'm going to produce a stack for each of the 3 different exposure lengths and experiment with blending them together to hopefully result in a core thats not blown out.
 

Ref light polution, I don't have anything as yet  its on the 'to purchase' list. its a toss up between an LP filter and a dew heater next. Then guide cam etc etc

[almcl]

18 minutes ago, edarter said:

Ref light polution, I don't have anything as yet  its on the 'to purchase' list. its a toss up between an LP filter and a dew heater next. Then guide cam etc etc

Welcome to the wallet emptying slope that is AP 🙂

 

[edarter]

18 minutes ago, almcl said:

Welcome to the wallet emptying slope that is AP 🙂

 

ooohhh yes!