Lightbeam appears in photos

[masjstovel]

Hi,

Shot the Pacman nebula last night and some time after meridian flip (At least thats when i noticed it), this beam of light appeared on all my next frames for about 4 hours.
Hopefully this is just a distortion from streetlights or something, and not sensor-related? Any clues?

[tooth_dr]

I have had something similar in my image - I put it down to a reflection. 

 

[masjstovel]

@tooth_dr Puh! And it was gone the next session again?
Looks very simular indeed. Out of curiosity, which focuser do you have? I have the Baader Steeltrack NT and its an "open base" (flat and not curved), so that i was thinking some light has sneaked in there.

[vlaiv]

1 hour ago, masjstovel said:

@tooth_dr Puh! And it was gone the next session again?
Looks very simular indeed. Out of curiosity, which focuser do you have? I have the Baader Steeltrack NT and its an "open base" (flat and not curved), so that i was thinking some light has sneaked in there.

It is extremely difficult to get such focused light on sensor from light leak - it needs to be focused by optical element or diffracted of an edge in the system.

[Jamgood]

Cobweb maybe?

[ollypenrice]

It looks pretty horizontal on here but in a single uncropped sub is the line literally pixel-perfect horizontal? If it isn't I doubt it will be electronic in origin.

Olly

[masjstovel]

@Jamgood There was actually cobweb around when i took down the rig this morning. But i didnt check inside the tube. You were serious right? Would that appear like this? 

@ollypenrice I though about that too initially, but i checked and its not horizontal. Its sliiiiightly offset leaning upwards on the right side. Btw, you see the star improvement considering my previous thread?

Edited October 14, 2020 by masjstovel

[Davey-T]

Have to check inside the dew shield on my SCT occasionally as there's usually a spider setting up home in there.

Dave

[ollypenrice]

5 minutes ago, Davey-T said:

Have to check inside the dew shield on my SCT occasionally as there's usually a spider setting up home in there.

Dave

 

1 hour ago, Jamgood said:

Cobweb maybe?

But wouldn't this create spikes coming out of all the stars? (Like Newt diff spikes?)

Olly

[Jamgood]

30 minutes ago, ollypenrice said:

 

But wouldn't this create spikes coming out of all the stars? (Like Newt diff spikes?)

Olly

I would have thought so, yes but I'm no expert. Interesting that there were cobwebs around though.

1 hour ago, masjstovel said:

@Jamgood There was actually cobweb around when i took down the rig this morning. But i didnt check inside the tube. You were serious right? Would that appear like this?

As above, I'm no expert and it was just a suggestion but as @ollypenrice said, you would expect to see extra diffraction spikes from all stars.

It is strange that the line tapers in and out across the image. Is it in the same place in every image or does it move when you dithered, etc?

Edited October 14, 2020 by Jamgood

[ollypenrice]

45 minutes ago, Jamgood said:

 

It is strange that the line tapers in and out across the image. Is it in the same place in every image or does it move when you dithered, etc?

That's something I, too, thought odd. It seems more like an optical phenomenon for that reason. You'd say a flaring satellite except that it's repeated on multiple frames (or so I understood?) This similarity with Adam's line is also striking.

Olly

Edited October 14, 2020 by ollypenrice
Typo

[tomato]

Wouldn’t you need something a bit more substantial than a spider’s thread in front of the objective to create this effect, and anyway I agree it would more likely originate  from bright point sources in the image.

I can get flares from nearby bright stars in an image (left of M106 in the attached) but they are never as clean and distinct as these.

Edited October 14, 2020 by tomato

[Davey-T]

21 minutes ago, tomato said:

Wouldn’t you need something a bit more substantial than a spider’s thread in front of the objective to create this effect,

I've experimented on a refractor with everything from fuse wire to half inch dowels and it seemed that diffraction spikes were diffraction spike and not much affected by what made them.

Dave

[masjstovel]

@Jamgood Its stationary yes. Thats why i thought reflection, since its "coming in and out" regarding luminosity.

@ollypenrice Correct, it wasnt there for say 4 hours, then it was there for the next for hours. The difference in luminosity in the way it appears with most brightness in the middle and less on the sides makes me feel its not sensor/camera-related. 

@tomato I understand what you're saying, but then its strange it suddenly appears after hours of frames. I'm shooting at the same target now by platesolving, and its not there now. Doubt it has anything to say, but yesterday it appeared on both Ha and OIII at the same brightness, but today im shooting with SII. 

[tooth_dr]

Moisture in the air, and something reflective within the imaging train or edge of secondary mirror, causing the right circumstances.  I had the same issue where it was there for a few hours and not there another night.

[masjstovel]

Heres Ha integrated: 
Seems it moves a little, or its an extra beam luminating that doesnt have enough brightness for the eye in 1 frame (?)

[tooth_dr]

Thats pretty bad

[masjstovel]

@tooth_dr I will try to photoshop it out i think. 

[ollypenrice]

8 hours ago, masjstovel said:

@tooth_dr I will try to photoshop it out i think. 

Shoudln't be too difficult. If you have Noels' Actions (now called Pro Digital Astronomy Tools, I think) there's one called Remove Horizontal (or Vertical) Banding. I use it to remove a 3 pixel wide dead column on one old CCD camera so it should fix yours. I copy the image to make two layers and run the action only on the bottom layer. Then I activate the top layer and run the eraser over the repaired part, so the action is applied only where needed. If necessary you can rotate the image to make the line precisely horizontal though that might not be necessary.

Olly

Edited October 15, 2020 by ollypenrice

[masjstovel]

I'm finished processing now. Got the light ray removed - if you don't know it wasn't there you wouldn't see it is my conclusion.

 

Before:

After:

[ollypenrice]

On 16/10/2020 at 20:18, masjstovel said:

I'm finished processing now. Got the light ray removed - if you don't know it wasn't there you wouldn't see it is my conclusion.

 

Before:

After:

Result!

[Erling G-P]

I got a horisontal line too on this target, although mine is a litte lower than yours.  I also have a weaker, vertical one, on the other side of the nebula.  I never got completely rid of mine in the editing, short of clone-painting it out.  Someone else suggested it was reflections caused by bright stars outside the view - see the attached small image.

[masjstovel]

Might very well be. Shedar is pretty bright i think. Strange it wasnt present on all the frames though, but yes, that might very well be the sollution!