Whats this on my image?

[iwols]

Hi can anyone throw light on he circle at the bottom of the image,same on all filters,C8 edge with reducer

[ONIKKINEN]

Looks like a dust spot on one of the lens surfaces. Could be any of the lenses in the corrector or on the camera itself. Since it happens on all of your filters its not on any of them and they can be ruled out. Nothing to worry about though, you don't even need to clean it since that will calibrate out with flats just fine.

[newbie alert]

Looks like dust very close to the sensor

[iwols]

thanks guys use the rocket blower and now ok