Extra diffraction spike

[lukebl]

Any idea where the extra diffraction spike in this highly cropped image is coming from? The fainter one running at 45 degrees from top left to bottom right of the bright star.

It's a 250PDS f.4.8 Skywatcher Newt, with a Baader coma corrector and an Atik 383L+.

 

[doublevodka]

9 minutes ago, lukebl said:

Any idea where the extra diffraction spike in this highly cropped image is coming from? The fainter one running at 45 degrees from top left to bottom right of the bright star.

It's a 250PDS f.4.8 Skywatcher Newt, with a Baader coma corrector and an Atik 383L+.

 

The end of the focuser tube sticking out into the light path would be my guess. A picture from the business end of the scope with everything setup and focused would help pinpoint it though 👍

[wulfrun]

Don't rule out something external, in addition to the posts above. Last year I was observing Jupiter from my back yard, through a scope with a 4-vane spider. I got 6 spikes but only the expected 4 on a few stars I tried for comparison. Turned out my washing line was smack in line with Jupiter!

[ONIKKINEN]

I also have an extra spike, but only sometimes. I have not figured out the cause and i have kinda just given up trying to troubleshoot it.

Focuser tube on mine is not obstructing the primary, there are no extra bits hanging in front of the scope or washing lines in the way. I suspect my coma corrector (TS maxfield) is the cause, but wont know for sure until i change it.

[Starflyer]

Prime suspects; focuser tube, mirror clips,  primary or secondary mirror edge roughness.

Can be a difficult problem to solve but it should be solvable.

[Dan_Paris]

Something like a screw intruding into the light path would make a more sharply defined spike. To me it looks like the effect of mirror clips.

Is it uniform across the frame ?