The case of overcor...
 
Share:
Notifications
Clear all

2022-05-29: APP 2.0.0-beta2 has been released !

Release notes

Download links per platform:

windows 2.0.0-beta2

macOS x86_64 2.0.0-beta2

macOS arm64 M1 2.0.0-beta2

Linux DEB 2.0.0-beta2

Linux RPM 2.0.0-beta2

The case of overcorrecting flats, need help

Page 3 / 3

(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4850
 

Thanks Simon, I'll download the data today and will try to check today or tomorrow (it's a birthday of my kid here so please allow for a day or 2). 🙂


ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 

@vincent-mod No problem at all, family first!


ReplyQuote
(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4850
 

Checking it right now;

I appear to see stars in the masterdark, can that be the case? If so, that might influence calibration for sure. You do need a bias signal for the lights as well, so that should come from a proper dark or a bias. I'm also wondering a bit if the over-correction is from the flats or you have residual light pollution actually coming from below.

 


ReplyQuote
(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4850
 

I also say this as the vignetting seems properly centered and is all around, but the light pollution model (after integration with the flats), doesn't show clear overcorrection all around.

image

ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 
Posted by: @vincent-mod

Checking it right now;

I appear to see stars in the masterdark, can that be the case? If so, that might influence calibration for sure. You do need a bias signal for the lights as well, so that should come from a proper dark or a bias. I'm also wondering a bit if the over-correction is from the flats or you have residual light pollution actually coming from below.

 

No chance of stars in the Master Dark, this is the Master Dark - Stretched of course

image

So I re-aligned the optics last night and did some imaging, new lights, new flats and after my post processing script has ran which also includes an Auto Background Extraction, this is the result:

image

So clearly it's not an LP thing, as the LP would not have the shape of vignetting for sure, it would be more of a gradient in a specific direction

 


ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 

A contour plot on each light stack clearly does show an LP Gradient though

Red:

image

Green:

image

Blue:

image

Lum:

image

 


ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 

After an ABE on each of the Light Masters, you can see that the light object is not in Blue at all

Red:

image

Green:

image

Blue:

image

Luminance:

image

The fact that it exists in Red, Green and Luminance, but not in blue indicates that it must be a light source that is only affecting Red and Green wavelengths, which of course Light Polution typically affects Green, and sometimes red, so you might be onto something with the light polution theory


ReplyQuote
(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4850
 

Yes, because normally, when you have flat over-correction, you'd see this happen on the dark parts of the vignetting, they all turn brighter. And I noticed in your case, it's only on the bottom and that almost can't be due to flat over-correction.

Regarding the masterdark you uploaded, this is what I saw:

image

Zooming into a region of what I think are stars:

image

If you're indeed taking darks during the night on the scope, these must be stars. They cover an area of pixels, not just 1 which would be a hot pixel.


ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 

@vincent-mod All my darks are done with the scope covered and the observatory closed, so this is strange indeed, and I just looked at what you are pointing out and the shape / size is repeated where you see this anomaly, in other words all the anomalies look the same.  I do not have the dark frames any more as I usually discard them when making the master dark, might re-run the darks again


ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 

Also just some insight as well, makes no difference whether my flats are 22500, 29500 or 45000 ADU, they all produce the same resulting stacked image, I think it helps that my camera is true 16-bit too, as I know certain things need to be taken into account when using 12, or 14-bit ADCs versus true 16-Bit

This post was modified 1 month ago by Simon Todd

ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 

Darks are correct, her's a zoomed in of a current 60S dark single frame, stretched of course

image

 


ReplyQuote
(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4850
 

Mmm, well, to us that dark does not look correct actually. Unless it's a type of glow we're not familiar with. Those bigger spots are not normal hot pixels anymore.


ReplyQuote
(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4850
 

Just as an extra check, how do you store your data? You're not working on external disks or disks which have a FAT32 system right? Or something like having the work-directory for APP, being on an external drive?


ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 

@vincent-mod All my files are stored on a NAS using EXT4 across a 10G link, my temp location is always my local NVMe drive as I want the fastest processing possible with my 18 core system 😀


ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 
Posted by: @vincent-mod

Mmm, well, to us that dark does not look correct actually. Unless it's a type of glow we're not familiar with. Those bigger spots are not normal hot pixels anymore.

I checked back on my ASI6200MC Pro as well, my master dark contains the same artifacts (but in different places), so perhaps this is just some camera chip anomaly, have asked ZWO for comment

 


ReplyQuote
(@wvreeven)
Galaxy Admin
Joined: 4 years ago
Posts: 1723
 

@stastro I checked the master dark of my ASI6200MM and it has this too. This is zoomed in on a random part

Screenshot 2022 05 30 at 22.23.05

and this zoomed in on one of the "dots"

Screenshot 2022 05 30 at 22.23.17

ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 

@wvreeven So it must be "Normal" then 😀

Have you tried platesolving your dark frame 😀

This post was modified 1 month ago by Simon Todd

ReplyQuote
(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4850
 

Fascinating! I've never seen that with a sensor. Ok, well then I guess it is normal. 🙂


ReplyQuote
(@stastro)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 81
 

So I wanted to close the loop on this one, after some extensive investigation, it turns out that the scope was picking up some stray light, adding a dew shield to extend the tube by around 5 inches has eliminated the issue, the following image was processed using my existing flats at 22.5K ADU (Which is what I was always using), and I have tried with 29K, and 45K ADU flats and the resulting image is the same.  I suspect I will have to re-do my flats with the dew shield though for completeness and to tidy the image up further.

image

 

image

ReplyQuote
Page 3 / 3
Share: