Strange circles in flats

@moviecells If you are talking about those dark circles, those are caused by dust specs and sometimes are referred to as dust devils. Judging by the size and the fact that you write that they are on all images with all filters, they are on the flattener. This is nothing to worry about and very hard to get rid off since there always is dust everywhere. As a matter of fact, flats have two main purposes: to get rid of vignetting and to get rid of dust devils. They are present in the lights as well, though harder to see, and creating a master flat and applying it to the lights will get rid of them.

Hi I have had dust issues before but this seems different they are still in final images see below. I also tried moving optics around like the angle of the camera, filterwheel and also the reducer but they are always in the same place. Also very strange is i can't see it in normal lights no matter how much i play with the histogram to see them. 

You may say then the dust was there when i took the flats but not there on the night of the lights but the lights are from two days ago i have take flats again today and the circle are back in the same place. so no difference in flats from about 2 weeks ago and now both are the same and show the circles.

This is final integrated image for lum

This is single light lum pulled the histogram to try and see if it was there no sign

Mike

Hi Could you look at my other post as again there may be a common problem here on my other scope the 14 inch meade flats again do not seem to process out and seem to over correct may be the same thing is happen here this is the post below go to the end the bit from today, i have added a link to the files if needed

https://www.astropixelprocessor.com/community/main-forum/flat-frame-not-being-applied/paged/3/#post-17680

Mike

@moviecells Mike, I don't see the dust ring on the integrated luminance image but maybe that's because of the way the image was shared. If rotating the optics doesn't introduce movement in the location of the dust rings then it may be a spot on the protecting glass of the camera or, worse, on the sensor itself.

Vincent unfortunately is not available today but I am sure he will reply to your post on or shortly after Monday.

Hi Being a optical engineer with Carl Zeiss i know a dust spot close to the sensor are going to be much more in focus and sharp even as far out as the filter ii my setup this looks to be long away from that area but more a worry is pixel processor does not seem to process it out of the final image if its there. may be vincent can help as you said i have just renewed my yearly license with a full purchase copy as up to now its been great just need to sort these problems out to get the best out of current setup

Mike

might try tomorrow to remove the reducer it not easy to rotate it to offset from the camera, as i said more worried why processing does not remove it.

mike

@moviecells You are right that a dust spot would be more focused. I meant a small stain, not a dust spot. But that was assuming that you had rotated the camera w.r.t. the reducer as you wrote in your comment of July 16 at 19:16. In general, however, such dark circles are produced by dust relatively far away from the sensor.

As for processing not removing it: once again, I don't see that in the images you posted. But judging by your other post as well, it looks like you have problems shooting flats in general which may very well explain this. Quick question related to that: in this comment you write that you take 1x1 bin lights and in this comment that you take 2x2 flats. Is that correct? If yes then that is the source of the issue. All lights and calibration files need to be taken at the same binning.

Hi Different setups i have two scopes one runs some times in bin2 but all my lights and flats match the bin setting i know you can't mix them.

mike

Hi Any idea what would cause my stars to form like little 6 shapes mainly in the corners this is zoom in. guiding seems fine it a meade 14 inch so long focal length.

Mike

Stars deforming in the corners is yet another optical effect caused by not having a perfectly flat-field. This is called coma.