Diffraction pattern on bright stars

[ajh499]

Hi

Does anyone have any suggestion as to the cause of the diffraction pattern around Alnitak in the attached image? 

The telescope is a SkyWatcher ed80 ds pro, and the camera an ASI 183 mm pro.

I've only noticed this issue with my last couple of images, but that may be due to not having bright stars in the images that often. 

I recently switched to an OAG, could that be the cause? There's no evidence of it on flats though. 

As nights seem to be permanently cloudy at the moment, is there a way to test for a pattern like this during the day? 

 

Thanks

 

Alex

[sharkmelley]

It looks suspiciously like microlens diffraction.

Mark

[ajh499]

3 hours ago, sharkmelley said:

It looks suspiciously like microlens diffraction.

Mark

On a 183mm?

I didn't think that happened with that sensor

Alex

[sharkmelley]

1 hour ago, ajh499 said:

On a 183mm?

I didn't think that happened with that sensor

It's the first example I've seen from the ASI183MM but the evidence here is quite conclusive.  It's very obvious in the blue channel.

The OAG won't be the cause and the only way you can reproduce this on a cloudy night is to use an incandescent (i.e. full spectrum) artificial star at a sufficient distance form the scope, so you can focus it..

Mark