ASI 1600mm-c: Strange pattern

cwalter

Hello,

when i don't use dithering i have a strange pattern in my pictures:

image.png

(extremly stretched to show the pattern)

After furter inspection i noticed that this pattern is also in my flats:

image.png

(background extracted with ABE in PI and also stretched)

It makes no difference which filter is used, or if i use my newton or the refractor.

I use a led box to generate the flats and very short exposures (for example 0.002s for L)

to generate the flats, but as the pattern is also in the lights that can't be the reason.

So where comes the pattern from? Could this realy be from the wafer saw and the polisher

as an astronomy friend of mine assumed?

Thanks and best regards

Christian

Sam@ZWO

how about longer exposure such like 1-2s and without any filter

cwalter

Sam wrote:
how about longer exposure such like 1-2s and without any filter

Hello Sam,

in my first post i have forgotten to write that the M81/M82 Picture is a stack of 70x180s. In a single Image the pattern isn't visible, but in the stack it is.

I tried some longer exposured flats without the filter wheel:

Unbenannt2.JPG

In a 0.1 single flat it is clearly visible after background extraction and stretching in Pixinsight. In a 3.5s flat (with the help of uncountable sheets of paper) i can't see this pattern, but stacking of some flats revealed it:

Unbenannt.JPG

But the flats aren't the Problem. The Problem is that i have this pattern also in my lights in some cases (it depends on the background and the image processing). So what could be the reason for this pattern?

Thanks and best regards,

Christian

manuelj

cwalter

Hello Sam,

i still have the question where these patterns come from - another example:

M51.JPG

i have used dithering, but that won't hide the pattern and also lights won't correct the problem entirely.

As sayed before i can't see those patterns in every pictures. It depends on the object, the background and how much i have to stretch the picture. But at the moment it seems that i can't make pictures of galaxies with this camera - so what could be wrong?

Best regards,

Christian

Sam@ZWO

I am not sure where is the problem

but can you calibrate it with the flat?

manuelj

timn

I had a pattern in my flats until I increased my time above a second. I'm now around 2 seconds and haven't had a problem since.

In your lights it looks like a type of walking noise that you get without dithering. Try increasing your dithering to a more extreme dither and remember to stack with a sigma rejection method. Hope this helps.

james_screech

Are you using a mains power supply? If so could you try another 12v source (if possible a battery), it could be a visual representation of mains hum if the supply is not smooth enough. Or you may have a ground loop.

bvalente

cwalter wrote:
Hello,

when i don't use dithering i have a strange pattern in my pictures:

image.png

(extremly stretched to show the pattern)

After furter inspection i noticed that this pattern is also in my flats:

image.png

(background extracted with ABE in PI and also stretched)

Christian

Christian do you have some unprocessed fits files to look at?