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tooth_dr

Diagnosis of artefact?

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Anyone seen this sort of thing?

Modified 40d camera, on an ED80, with FF.

 

 

Artefacts.jpg

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Those look very much like diffraction spikes. I have seen that when the telescope was pointing low enough for a power or telephone cable to get in the way.

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Did you clean your optics, like a focal reducer, and left some streaks?

 

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1 minute ago, MarsG76 said:

Did you clean your optics, like a focal reducer, and left some streaks?

 

I bought two second hand FFs, and a used ED80 scope.  It's not in the 1000d pointing at the same objects at the same time.  I'd need to swop the camera over as that would rule out a lot of problems.  Just wondering if anyone had any ideas!

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3 minutes ago, tooth_dr said:

I bought two second hand FFs, and a used ED80 scope.  It's not in the 1000d pointing at the same objects at the same time.  I'd need to swop the camera over as that would rule out a lot of problems.  Just wondering if anyone had any ideas!

Unless you do have some powerlines in the way, really the only place you can investigate is in your optics.

Swapping the camera will take that out of the problem equation so it is a good idea, but IMHO those diffraction spikes do not look like they are caused by the camera, they are a clear refraction.

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25 minutes ago, michael.h.f.wilkinson said:

Those look very much like diffraction spikes. I have seen that when the telescope was pointing low enough for a power or telephone cable to get in the way.

Subs taken at same time, one with 40d and one with 1000d, see below.  I just need to swop over the cameras and see if that affects it.

 

Artefacts2.jpg

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Are you by any chance using OAG?

Prism in light path on one side can produce artifact like that - only on bright stars, and only on one side of image.

Other than that - I would look for sharp edges in one side of optical train since stars in lower part of field don't have it - only in upper.

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2 minutes ago, vlaiv said:

Are you by any chance using OAG?

Prism in light path on one side can produce artifact like that - only on bright stars, and only on one side of image.

Other than that - I would look for sharp edges in one side of optical train since stars in lower part of field don't have it - only in upper.

No not using OAG.  I am using a Baader click lock on that scope, to allow rotation of camera. No filters used.  The attached images above are crops.  Here is full frame below, it does seem to affect the stars in the top of the field though as you say.

 

 

Artefacts3.jpg

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1 hour ago, tooth_dr said:

No not using OAG.  I am using a Baader click lock on that scope, to allow rotation of camera. No filters used.  The attached images above are crops.  Here is full frame below, it does seem to affect the stars in the top of the field though as you say.

 

 

Artefacts3.jpg

Besides switching camera, you might try to rotate camera - if artifact persists in same place (top - top left corner) - source of it is in assembly that rotated. If it changes position - it is not related to rotated assembly (camera and what ever there is attached to it).

Due to orientation of artifact I would have strong suspicion it is camera related. It is almost (I can't tell with 100% certainty) vertical - implying that source is horizontal. Straight lines related to camera do tend to be either vertically or horizontally oriented in relation to sensor. But like I said, I can't be 100% certain - it looks like spikes are vertical, but may be a degree or two off from true vertical.

 

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The pattern looks a bit like very low resolution spectra which would imply there is something that is acting as a bit of a diffraction grating.

I wonder whether it is the underside of the mirror on the camera and it has a slightly rough surface?  That would align to the idea that there is something horizontal in the light path.

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2 minutes ago, Whirlwind said:

The pattern looks a bit like very low resolution spectra which would imply there is something that is acting as a bit of a diffraction grating.

I wonder whether it is the underside of the mirror on the camera and it has a slightly rough surface?  That would align to the idea that there is something horizontal in the light path.

 

Thanks for the suggestion. When it’s clear I’ll check and try a few things. 

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