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Part of the California Nebula in HA

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8 hours ago, red dwalf said:

Strangely enough the smudge shows up on the flats, i think I've narrowed it down to the reducer or camera lenses.


smudge on screen



Morning Rob,

  That's the idea. If it shows up on the flats, and on the lights, it should subtract out and not be there on your processed image..

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1 hour ago, red dwalf said:

Tried that Dave, did 41 flats but it still showed on the stacked image leaving a funny dark patch where the smudge is on the flats

Hmmm. It's always easy to comment, not so easy to get the real solution. Unless you have a cooled camera, the flats are going to be taken at a different temperature, so maybe that's part of the answer?

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I don't see any obvious 'smudge' in the image you posted in the area that has the 'smudge' on your flat image.  Is it actually there on the raw image or did it only appear after applying the flats to the image?


In applying the flats to an image, the image is the numerator and the flats are used as the divisor, so, for the resulting image to show a darker region after a flats have been applied, the flat 'smudge' must be 'brighter' than the image 'smudge'.

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In the image there aren't any flats added, I wanted to add some but after I took the flat I noticed the smudge on the flats only which was strange, I did try adding the flat files but the smudge showed up on the final image and I found it difficult to process out without it being obvious, last night I added my Canon 1100D to the scope did some flats after imaging M31 and no signs of the smudge, I did clean the focal reducer first so hopefully something on the reducer was the problem, will try doing some flats again when I change cameras back. 

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