Any ideas for what this is - Tak106 and Atik 4000?

[cfpendock]

Last night was murky and cold, but stars were visible so I set up to image NGC2403, a smallish galaxy to the north-east.  I took 16 x 300 seconds each of LRGB.  Today I looked to see what I had got, and found strange lines (like edge-on galaxies) but all in the same plane.  I also noticed some diffraction spikes, also in the same plane, on some of the stars.  The artefacts are present on all filters so they can be ruled out.  The camera (Atik 4000) also looks absolutely clean, as does the glass in the scope (Tak106ED).  When we get another chance to see stars I will rotate the camera through 90 degrees to confirm if it is the camera or scope.

The artefacts are only present in a few places, generally on the left of the image.  I have never seen anything like this.  I don't think it could be ice - I use a dew heater (and it was working) and normally ice on the camera chip disappears within 20 minutes, and in any case does not look like this.  

Attached is a linear stretch of the Luminance, with enlargements to show a few of the artefacts .

Any ideas would be most gratefully received.

Chris

 

[Knight of Clear Skies]

Does seem odd, could you post up a single sub please?

[ollypenrice]

Well, congratulations on having produced something I don't think we've seen before! The horizontal spikes through stars are not unknown but the spurious 'edge on galaxies' are new, certainly to me. From what I can see here all three bear a striking resemblance to each other in terms of shape, orientation and that whispy hint of a 'keel' on the underside. Is this borne out by closer inspection? It maybe implies a common cause, such as a reflection reappearing in several places. I still wonder if it might be a tiny ice particle somewhere in the optical train?

Olly

[cfpendock]

Thanks, Knight of Clear Skies.  Sure, all subs were similar, here is one:

11 minutes ago, Knight of Clear Skies said:

could you post up a single sub please?

 

 

3 minutes ago, ollypenrice said:

a reflection reappearing in several places.

Thanks for your comment, Olly.  Yes.  That had occurred to me - possibly off the OAG which perhaps was a little too far into the optic space, although well clear of the line to the camera chip, which  of course is rather smaller than the Atik11000.....

[ollypenrice]

Just now, cfpendock said:

Thanks, Knight of Clear Skies.  Sure, all subs were similar, here is one:

 

 

Thanks for your comment, Olly.  Yes.  That had occurred to me - possibly off the OAG which perhaps was a little too far into the optic space, although well clear of the line to the camera chip, which  of course is rather smaller than the Atik11000.....

Not a bad line to pursue. (The image circle of the 106 is so vast that no known chip will leave you short of OAG illumination!)

Olly

[Thalestris24]

Hi

I've had those sort of artifacts before - but with a lens and a Ha filter on the front. It was obviously some kind of reflection between the front of the lens and the back of the filter. Good news was that they completely disappeared with dithering and kappa-sigma stacking

Louise

[cfpendock]

Thanks Louise.  The thing is that I've used this combination probably more than one hundred times before, but I've never seen anything like it.  I am not sure about the reflections because the artefacts are only on certain stars.  I use kappa-sigma stacking anyway, but the artefacts are on every sub, so they would be treated as part of the image.

I just need some clear skies to experiment.....

CHRIS

[Robd]

We have overhead electric cables crossing the garden,  1 support post 2m south of observatory,  4 cables running approx. east west.  I get similar spiking when cables are in field of view. 

Right pain because I rarely think to check.

[Knight of Clear Skies]

20 minutes ago, Robd said:

We have overhead electric cables crossing the garden,  1 support post 2m south of observatory,  4 cables running approx. east west.  I get similar spiking when cables are in field of view. 

I wonder if whatever is causing the streaks, whether it's inside the optics or not, could explain the darkening on the left hand edge of the frame as well.

[Gina]

The spikes and pseudo edge-on galaxies are all the same angle - just a little off horizontal in the frame so evidently spurious and all with the same cause.  Very strange - never seen anything like it myself.

[cfpendock]

2 hours ago, Robd said:

We have overhead electric cables crossing the garden,  1 support post 2m south of observatory,  4 cables running approx. east west.  I get similar spiking when cables are in field of view. 

Nice idea, Robd.  In fact in November I had postponed imaging this galaxy precisely because a poplar tree was partially hiding it.  I intended to try again in Feb, but eventually tried again in late Jan, when indeed the galaxy appeared to be clear of the tree.  However, the spikes show in all the subs, taken between around 7pm and midnight.  Close to midnight the galaxy was certainly well clear of the tree and around 70° altitude, but the spikes are in exactly the same place.  So I don't think this is the answer.

 

1 hour ago, Knight of Clear Skies said:

I wonder if whatever is causing the streaks, whether it's inside the optics or not, could explain the darkening on the left hand edge of the frame as well.

Could be.  Or is this the tree?  I need to investigate the subs more carefully.  But I can't really do anything about it now because of the weather which I understand will continue to be bad for some time.  In the meantime I have repositioned the OAG mirror, and checked all the glassware.

Chris

[Thalestris24]

Here are some examples of mine from last year - just stretched single sub jpegs (Takumar f4 200mm, Baader 7nm Ha, mono 550d):

 

 

 

 

The gradient visible in some subs is caused by a streetlight. There are no especially bright stars in any of the images and none nearby. I've only had the artifacts with the Ha filter at the front of the lens so it's obviously something to do with that. You can sometimes see 'ghosts' of the main artifact, and in the 3rd sub, a second artifact. As I mentioned, they disappear with kappa-sigma stacking in dss. I would have been dithering. 

Louise

ps the horizontal noise in the 3rd sub were probably a sign that the camera was failing  Am awaiting repair...

[cfpendock]

3 hours ago, Thalestris24 said:

Here are some examples of mine from last year

That's interesting, Louise. Normally I would think the main artefact was a fault with the chip, or possibly the Ha filter - presumably your Ha exposures are much longer than for LRGB, and except for the 3rd sub, it is just one artefact, always in the same place, and reasonably bright.  Perhaps it will all disappear when the camera is repaired.  Mine appear in all filters.  I need to do some tests but the weather......

Chris

[Thalestris24]

2 hours ago, cfpendock said:

That's interesting, Louise. Normally I would think the main artefact was a fault with the chip, or possibly the Ha filter - presumably your Ha exposures are much longer than for LRGB, and except for the 3rd sub, it is just one artefact, always in the same place, and reasonably bright.  Perhaps it will all disappear when the camera is repaired.  Mine appear in all filters.  I need to do some tests but the weather......

Chris

Hi Chris

It wasn't the sensor it only appeared on subs with the Ha filter attached to the lens. I couldn't see anything wrong with the filter. If you look carefully in the first one there are ghost artifacts and in the third sub there is that additional artifact. The individual subs have bee stretched a bit. I'm pretty sure it's some kind of reflection from streetlights with the filter just in front of the lens glass. As I say, all goes away with dithering and kappa-sigma stacking.

Louise

[Thalestris24]

Hi Chris

It's interesting that you have the horizontal lines through some of your stars - must be a clue! Were you dithering, by the way? If not, that might be a way to get rid of them.

Louise

[cfpendock]

On 2/2/2017 at 12:38, Thalestris24 said:

Were you dithering, by the way?

No.  I've tried dithering before but it never made any discernible difference to my images.  I could try it, but I have lots of other things to try first.  But thanks for the suggestion, Louise.  I will post the results of testing - when the weather permits!

Chris