M97 (Owl Nebul) and M108

[Adam1234]

It was my first time guiding last night, and I set my sights on the Owl Nebula and the galaxy M108. After playing around getting focus on the guide camera, PhD2 seemed really easy to use. It seemed to guide ok and I'm really pleased with how my images have come out, I was doing 600s exposures!

21 x 600s lights (3.5 hours); 6 x darks; 40 x flats; 40 x flat darks. Canon 2000d, SW EQR-6 Pro, SW ED80 DS-Pro, guided with ZWO ASI 120mm mini. 

 

Adam

 

 

Edited April 13, 2020 by Adam1234

[MarkAR]

Well done, looks like guiding has worked. My screen is showing quite a bit of green tinge though.

[Adam1234]

13 minutes ago, MarkAR said:

Well done, looks like guiding has worked. My screen is showing quite a bit of green tinge though.

Thanks! Yeah my phone is also showing a green tinge even though it looked fine on my laptop. Strange. I will have a go to reduce some of that green in a bit.

[Jiggy 67]

Nice image, stars appear sharp and and the galaxy and nebula show nice details when you zoom in, you could crop them into two nice photos as well . A green tinge yes, but doesn’t take away any enjoyment 

Edited April 13, 2020 by Jiggy 67

[ollypenrice]

The green bias is overwhelming but can certainly be fixed.

Olly

[Adam1234]

Had a go at trying to reduce the green, so let's see how it looks. No idea how to get stars with natural colours. Mine all come out the same colour.

Done some cropped images too. The cropped images would definitely benefit from several more hours exposure. Probably better targets for a long focal length scope.

[Adam1234]

Hmmm looked ok on my laptop but on here (using my phone) still hideous green tinge

[MarkAR]

Yup, still green.

What software did you use to stack?

I know Siril and Pixinsight both have a green noise reduction tool that gets rid of it.

[Adam1234]

10 hours ago, MarkAR said:

Yup, still green.

What software did you use to stack?

I know Siril and Pixinsight both have a green noise reduction tool that gets rid of it.

Hmmm. I wonder why it looked ok on my laptop but not on other devices. Maybe not balancing the colours right? Could it be that I used a too long exposure for a light polluted area? I've not ended up with a green tinge before. 

I used Deep Sky Stacker. I tried using Siril the other week but it's a bit confusing and not sure how to use it properly so I gave up attempting to stack with Siril. 

The stacked image didn't have a green tinge, more blue actually because of the LP filter I'm using, so it's probably from the post processing.

 

[MarkAR]

Not sure what's causing it except difference in computer screens.

I've used Siril a few times with a little success, I found a YT tutorial that shows you how to use the scripts which is almost like a Push Here Dummy set up.

https://www.youtube.com/watch?v=iVVv5mIb8U0

 

[alacant]

8 hours ago, Adam1234 said:

The stacked image

Hi. How about posting -a link to- the stacked image with no processing?

Cheers

[Nicola Hannah Butterfield]

@Adam1234try calibrating your laptop for colour balance. You could try a magenta filter in gimp or photoshop, or any other editing software.

With your permission I can show the effect.

Edited April 14, 2020 by Nicola Hannah Butterfield

[Adam1234]

 

On 14/04/2020 at 18:15, Nicola Hannah Butterfield said:

@Adam1234try calibrating your laptop for colour balance. You could try a magenta filter in gimp or photoshop, or any other editing software.

With your permission I can show the effect.

How do you calibrate the laptop?

 I have no objections, I'll try and remember to share the unprocessed stacked image tomorrow when I'm on my laptop.

 

[Nicola Hannah Butterfield]

11 hours ago, Adam1234 said:

 

How do you calibrate the laptop?

 I have no objections, I'll try and remember to share the unprocessed stacked image tomorrow when I'm on my laptop.

 

There is a basic calibration routine in windows, click start button and type display colour calibration and follow the prompts, it might take a few attempts, it also adjusted brightness contrast.

There are devices you can get that do it better but not cheap.

[Nicola Hannah Butterfield]

Ok the first is with a quick magenta filter

 

This one with a colour balance layer, this allows highlights mid tones and shadows to be adjusted separately

Both could do with a bit extra, but a pretty simple fix to a green cast.

 

[Adam1234]

That's looking a lot better thanks, I will try that out myself

[Nicola Hannah Butterfield]

Just now, Adam1234 said:

That's looking a lot better thanks, I will try that out myself

Just to add I edited in photoshop, but gimp and other software will allow similar effects.

[Adam1234]

10 hours ago, Nicola Hannah Butterfield said:

Ok the first is with a quick magenta filter

 

This one with a colour balance layer, this allows highlights mid tones and shadows to be adjusted separately

Both could do with a bit extra, but a pretty simple fix to a green cast.

 

On my laptop your go at my image now looks like it has a slight magenta tinge, while on my phone it looks lovely. But also on my laptop, my image looked ok, but on my phone is awful. Really weird. 

I did look up about calibrating my laptop screen but most instructions were for an external monitor, which didn't really help much. When I went through the process everything appears to be correct according to the instructions 🤔

 

I've got the stacked tif image here if it uploads

Autosave.tif

[MarkAR]

Not sure if this will show anything, set computer and phone screens to white and compare.

Might show up something.

Not sure if this will help but do you have a display set up feature? this is the default Apple one.

[Nicola Hannah Butterfield]

@adam1234

Hows this.

 

adam1234_owl_nebula_ABE.tif

Edited April 16, 2020 by Nicola Hannah Butterfield

[alacant]

Hi

On 14/04/2020 at 10:01, Adam1234 said:

I used Deep Sky Stacker.

Nice shot.

JTOL. Was the bayer pattern set RGGB? There is very little red and there is a 'grid' pattern on the original.

One tip: lose any dark frames. Stick to light, bias and flat but dither a few pixels between light frames. Stack using a clip algorithm. I think dss has sigma clipping.

I'm hopeless on colour but had a go anyway and fixed a few of the stars. But to repeat, excellent effort:)

Cheers

 

Edited April 17, 2020 by alacant

[Adam1234]

1 hour ago, alacant said:

Hi

Nice shot.

JTOL. Was the bayer pattern set RGGB? There is very little red and there is a 'grid' pattern on the original.

One tip: lose any dark frames. Stick to light, bias and flat but dither a few pixels between light frames. Stack using a clip algorithm. I think dss has sigma clipping.

I'm hopeless on colour but had a go anyway and fixed a few of the stars. But to repeat, excellent effort:)

Cheers

 

 

 

Thanks alacant! How do I check the bayer pattern? Is RGGB what it should be, or should it be something else? I did see that 'grid' pattern emerge if I tried stretching too much, no idea caused that!

Why do you say to lose the dark frames, are they just adding noise rather than taking it away? Should I still do flat darks or do bias instead of flat darks? Sorry, lots of questions!

 

I think I've been stacking with the median kappa sigma clipping - although I just found this in the DSS Technical Info (last line):

'Background Calibration
The Background Calibration consists in normalizing the background value of each picture before stacking it.
The background value is defined as the median value of all the pixels of the picture.

Two options are available.

• With the Per Channel Background Calibration option the background for each channel is adjusted separately to match the background of the reference frame.

• With the RGB Channels Calibration the three red, green and blue channels of each light frame are normalized to the same background value which is the minimum of the three medians values (one for each channel) computed from the reference frame. On top on creating compatible images (stacking wise) this option is also creating a neutral gray background. A side effect is that the overall saturation of the stacked image is quite low (grayscale look).

It is important to check one of these options when using Kappa-Sigma Clipping or Kappa-Sigma Clipping Median methods to ensure that the pictures being stacked have all the same background value.'

 

 

[Adam1234]

14 hours ago, Nicola Hannah Butterfield said:

@adam1234

Hows this.

 

adam1234_owl_nebula_ABE.tif 121.2 MB · 1 download

That's wonderful!

[alacant]

1 hour ago, Adam1234 said:

How do I check the bayer pattern? Is RGGB what it should be,

Hi

I think in DSS it will take the pattern from the cr2 so you shouldn't have to do anything. I'm trying to ascertain the origin of the grid pattern. IIRC, AHD does a better job than the bilinear default. Maybe try that with the same frames?

1 hour ago, Adam1234 said:

Why do you say to lose the dark frames

IMHO and with the impossibility to be able to temperature match dark frames with the light frames, they introduce more noise.

Make a master bias from say 50 frames. Subtract this from both the light and flat frames. Make a master flat by stacking the bias calibrated flat frames. Now divide each light with the master flat and debayer the result. Register and stack using sigma clip. A few minutes in Siril (method here). I gave up on dss some time ago;)

HTH

[Adam1234]

1 hour ago, alacant said:

Hi

I think in DSS it will take the pattern from the cr2 so you shouldn't have to do anything. I'm trying to ascertain the origin of the grid pattern. IIRC, AHD does a better job than the bilinear default. Maybe try that with the same frames?

IMHO and with the impossibility to be able to temperature match dark frames with the light frames, they introduce more noise.

Make a master bias from say 50 frames. Subtract this from both the light and flat frames. Make a master flat by stacking the bias calibrated flat frames. Now divide each light with the master flat and debayer the result. Register and stack using sigma clip. A few minutes in Siril (method here). I gave up on dss some time ago;)

HTH

 

Re the dark frames, that makes sense. I'll try ditching the dark frames then until I invest in a cooled CCD (knowing me and my constant need for perfection that probably wouldn't be that long 😀). I can use the time I would normally spend taking darks by getting more lights (or sleep).

I'll give that video a watch and see if it's any easier to understand than another video on Siril I watched - my first impressions of Siril were that it's really confusing and I gave up after my first attempt.