Strange diffraction pattern

[skyrunner]

I was imaging the Jellyfish nebula in Ha with my WO Megrez 72 refractor a few evenings ago and after stacking found this strange diffraction pattern around the very bright star in the frame. I've never seen this before in any of my previous images. Any ideas what might have caused it? Could it possibly be due to frost on my camera window - I'm using an ASI178MM cooled CMOS camera.

I'd be grateful for any suggestions.

Thanks

Gordon

[carastro]

Unfortunately some of the CMOS cameras seem to suffer from this, it is called Microlensing.  I can;t offer any advice and not sure if there is a solution, perhaps others will know.

Carole 

[skyrunner]

Thanks, Carole, I've not heard of this before - I'll have a search and see what I can find.

Gordon

[carastro]

There is a thread on it on Cloudy Nights, and you can see the image in the first post looks like yours:

https://www.cloudynights.com/topic/646966-zwo-asi1600mm-pro-bright-star-issue/?hl=%2Bmicrolensing#entry9084570

Carole 

[vlaiv]

That has been seen a number of times with ASI1600 but never with ASI178 - at least not that I'm aware of.

If you can, try changing distance between components (presumably you do have filter and/or field flattener on that setup).

[skyrunner]

So another unusual phenomena last night. Imaging the Rosette Nebula in Ha my images appear covered in lots of 'dust bunny' type defects. But after I switched target to the Fishhead Nebula in a different part of the sky those images appear fine - see side by side images from same area of sensor after calibration and stacking. Also taking some flats this morning they all appear clean. The only thing I can think of is that the Rosette was quite close to the moon, probably about 20 degrees away. Perhaps this is also the microlensing phenomenon as a result of the high level of sky brightness close to the moon?

Gordon

Edited February 7, 2020 by skyrunner

[vlaiv]

47 minutes ago, skyrunner said:

So another unusual phenomena last night. Imaging the Rosette Nebula in Ha my images appear covered in lots of 'dust bunny' type defects. But after I switched target to the Fishhead Nebula in a different part of the sky those images appear fine - see side by side images from same area of sensor after calibration and stacking. Also taking some flats this morning they all appear clean. The only thing I can think of is that the Rosette was quite close to the moon, probably about 20 degrees away. Perhaps this is also the microlensing phenomenon as a result of the high level of sky brightness close to the moon?

Gordon

That looks like Newton's rings - but I have no idea of how they could have formed.

See here for details:

https://en.wikipedia.org/wiki/Newton's_rings

It is phenomena that sometimes creates issues for Ha solar imaging and tilting the sensor is solution for it. I wonder if Moon somehow gave enough light for those to develop (for some reason).

[darkairmouse]

Just to add here another evidence to show the possible microlens pattern with an ASI178MM..

 

Edited February 5, 2021 by darkairmouse