Circles in the flat images

[wangwill]

Hi,

I have an Atik 314L. I tried to take some flat images today, however 2 big circles were found in every images. Anybody know the reason?

As you see in the attached image. I think the white arrow is the dust on the ccd, what is the black arrow?

Additionally, how to remove the dust on the ccd? The ccd seems to be sealed.

Thanks in advance.

Best wishes.

[bwa]

If it is dust somewhere in your light train, flats should remove it.

bwa

[wangwill]

Thanks, bwa

Best wishes.

[joelshort]

The larger the dust circle on the flat, the further away from the CCD it is.  Take a look at your filters or your objective lens/mirror.  But a little dust is no big deal and the whole purpose of flats is to correct for dust and other issues.

[wangwill]

Thanks, joelshort. If it is due to dust, not a big issue.