processing help

[Anthonyexmouth]

Hi, been away from imaginig for a mere 6 months but forgotten the little I had learnt.

Could someone take a look at this and advise me how to best process this. At the moment I only have DSS, APP and GIMP. Can't remember how to remove the light pollution or gradient. 

Many thanks. Also, any advice on what is wrong with the data itself would be appreciated. Can provide all raw data if anyone is bored. lol

 

Autosave.tif

[happy-kat]

Two GIMP users are @alacant and @vlaiv perhaps one will see your post.

[vlaiv]

Just a preliminary stretch in Gimp to see what is there:

There is quite a bit of gradient that needs to be removed. I don't remove gradients in Gimp - I use my own tool for that. I'll do it later and post results (and tool if someone wants to use it - it is plugin for ImageJ).

[alacant]

Hi

Here are the stretched, darkened-blurred, mask and final images. To lose the gradient, subtract the blur from the stretched, then process it to taste. 

HTH

EDIT: don't forget to mask the stars before you stretch any more;)

Edited March 27, 2020 by alacant
forgot the mask

[Anthonyexmouth]

1 hour ago, alacant said:

Hi

Here are the stretched, darkened-blurred, mask and final images. To lose the gradient, subtract the blur from the stretched, then process it to taste. 

HTH

EDIT: don't forget to mask the stars before you stretch any more;)

that looks really nice, can you tell me the process and software used. 

[geeklee]

Here's some work in APP Anthony as you mentioned that software.  Just Light Pollution Removal and resize (50%) + rotate.  Saved with the 15%, 3 Sigma, 0.0% base DDP stretch (so a bit much prob!)

[Anthonyexmouth]

1 minute ago, geeklee said:

Here's some work in APP Anthony as you mentioned that software.  Just Light Pollution Removal and resize (50%) + rotate.  Saved with the 15%, 3 Sigma, 0.0% base DDP stretch (so a bit much prob!)

thanks, with the tools in APP i've never really understood where the requested boxes should be placed on the image. 

[geeklee]

4 minutes ago, Anthonyexmouth said:

thanks, with the tools in APP i've never really understood where the requested boxes should be placed on the image. 

I've found with this type of shot, it's difficult as you want to generally get background sky and there's a lot of nebulosity around.  I did the following which is massively simplified but reduces gradient quickly - but probably loses some faint good stuff too!  The tool is so good, you can experiment easily enough.

Red boxes it thinks might be wrong, so only leave if you're sure.  Yellow ones, be careful of but (as stated by the author in a video/post I've seen) there could always be some.

Edited March 27, 2020 by geeklee

[alacant]

15 minutes ago, Anthonyexmouth said:

process and software

Hi

load - crop - stretch - duplicate - blur - darken - subtract - mask - blur - masked stretch - denoise 

GIMP

HTH

 

[vlaiv]

Here is my processing attempt:

It involves use of ImageJ and custom plugin, but I would be happy to both provide plugin and explain procedure for background removal.

[Anthonyexmouth]

I often notice when stretching the image that vignetting seems biased to one side, is there a way to correct this every easily on the SW ED80? Is it a collimation issue or just a result of the stock focuser? 

 

Also, had another go with APP and ended up with this. Seem to have a few large dust motes but looking at the optics I can't see any specks. Really annoying. 

Edited March 27, 2020 by Anthonyexmouth

[vlaiv]

55 minutes ago, Anthonyexmouth said:

Also, had another go with APP and ended up with this. Seem to have a few large dust motes but looking at the optics I can't see any specks. Really annoying. 

That is issue with calibration procedure. Probably faulty application of darks. If you used dark optimization it could produce this effect.

Btw - dust will be on sensor / filters and not on telescope optics.

[Anthonyexmouth]

1 minute ago, vlaiv said:

That is issue with calibration procedure. Probably faulty application of darks. If you used dark optimization it could produce this effect.

Btw - dust will be on sensor / filters and not on telescope optics.

Would that be dark optimisation in DSS or APP?

[discardedastro]

Gave this a go in PI - there's not much in terms of SNR between the fainter areas of nebulosity so a bit more exposure time will help that, but it's otherwise fairly clean data. Vignetting might be tilt, in which case you can get a tilt adapter for T2 trains - Teleskop Express do one - but it isn't significant and if you do flat fielding correctly should calibrate out nicely. Same goes for the dust motes, though cleaning is always preferable!

[Anthonyexmouth]

2 minutes ago, discardedastro said:

Gave this a go in PI - there's not much in terms of SNR between the fainter areas of nebulosity so a bit more exposure time will help that, but it's otherwise fairly clean data. Vignetting might be tilt, in which case you can get a tilt adapter for T2 trains - Teleskop Express do one - but it isn't significant and if you do flat fielding correctly should calibrate out nicely. Same goes for the dust motes, though cleaning is always preferable!

Thats good to know, I was running 3min subs on this with my 294mc pro. would longer subs be beneficial? don't want to swamp it or just more of them? 

[discardedastro]

32 minutes ago, Anthonyexmouth said:

Thats good to know, I was running 3min subs on this with my 294mc pro. would longer subs be beneficial? don't want to swamp it or just more of them? 

Just more of them, I think, though hard to say without seeing an individual sub.

[Anthonyexmouth]

Just now, discardedastro said:

Just more of them, I think, though hard to say without seeing an individual sub.

L_2020-03-26_20-58-12_180s_294mc__Color_G125_OFS22.fit

[vlaiv]

1 hour ago, Anthonyexmouth said:

Would that be dark optimisation in DSS or APP?

The one you used to calibrate / stack resulting image that shows dust shadows.

I'm guessing that you used same data as first stack. First stack does not show any issues with flat calibration - which means flats are fine.

Dark optimization works by scaling darks - something that you can do only if you use bias files and bias are stable enough (this seems not to be the case with CMOS sensors / cameras as far as I can tell). For this reason it is best to turn this option off as it can cause issues with flat calibration.

 

[Anthonyexmouth]

3 minutes ago, vlaiv said:

The one you used to calibrate / stack resulting image that shows dust shadows.

I'm guessing that you used same data as first stack. First stack does not show any issues with flat calibration - which means flats are fine.

Dark optimization works by scaling darks - something that you can do only if you use bias files and bias are stable enough (this seems not to be the case with CMOS sensors / cameras as far as I can tell). For this reason it is best to turn this option off as it can cause issues with flat calibration.

 

just checked DSS and dark optimisation was unchecked. 

[vlaiv]

1 minute ago, Anthonyexmouth said:

just checked DSS and dark optimisation was unchecked. 

What software did you use to stack this with?

Maybe you did not load calibration files? This image shows both issues with flats - dust shadows and issues with darks - there is amp glow visible in top right corner.

This could happen if you forgot to add calibration files or like I said, dark optimization was turned on for stacking and messed up dark calibration (hence both flat problems and visible amp glow).

 

[Anthonyexmouth]

2 minutes ago, vlaiv said:

What software did you use to stack this with?

Maybe you did not load calibration files? This image shows both issues with flats - dust shadows and issues with darks - there is amp glow visible in top right corner.

This could happen if you forgot to add calibration files or like I said, dark optimization was turned on for stacking and messed up dark calibration (hence both flat problems and visible amp glow).

 

If that was the autosave.tiff then DSS, otherwise it may be either DSS or APP thats then been tweaked in Gimp. 

[Anthonyexmouth]

Can't find any mention of Dark Optimisation in APP, anyone know if there is an option for that in APP?