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Old 03-01-2011, 11:59 AM
TrevorW
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Crop Circles and band in image

Refer attached file(s)

don't show up on any of the flats I used (although the flats used were not taken on the same night) or when the individual frames are stretched

however when applying curves to the rgb stacked frame they do

also when no flats applied same thing appears

the flats were taken two weeks ago and used in my previous image of M46 and this effect doesn't show up in that image

is it the flats or reflection issues or something else
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Old 03-01-2011, 01:30 PM
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Looks like reflections to me Trevor. You should always take your flats on the night as bits of dust etc will have collected/moved that would not have been there when the flats were taken. If you have broken down the mount and resetup on another night the flats you took 2 weeks previously will not work.

Mark
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Old 03-01-2011, 02:45 PM
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Quote:
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Looks like reflections to me Trevor. You should always take your flats on the night as bits of dust etc will have collected/moved that would not have been there when the flats were taken. If you have broken down the mount and resetup on another night the flats you took 2 weeks previously will not work.
I would have guessed dust rather than reflections.

Trevor, even if you had shot flats on the same night, do you do individual flats for each of L, R, G and B? Dust would be in different places on different filters.
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Old 03-01-2011, 03:01 PM
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I have seen this as dust as well.
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Old 03-01-2011, 03:12 PM
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Andrew One Shot Colour camera

annoying these things, is it not
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Old 03-01-2011, 04:50 PM
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Originally Posted by TrevorW View Post
Refer attached file(s)

don't show up on any of the flats I used (although the flats used were not taken on the same night) or when the individual frames are stretched
Then the dust motes probably have built up since.

Quote:
however when applying curves to the rgb stacked frame they do

also when no flats applied same thing appears

the flats were taken two weeks ago and used in my previous image of M46 and this effect doesn't show up in that image

is it the flats or reflection issues or something else
Dust motes. Large rings are likely on the mirror. Smaller, more defined spots would be on the ccd chamber window or ccd chip. Cant be the flats if you didnt use them ?? *confused

Get a flat from the same night next time, to compare?

Do you have an outdoor patio light? When your done, point the scope towards it; put a white shirt over, or opaque paper for an even illumination and take some flats at a exp time where you can see these nasties.

Last edited by leinad; 03-01-2011 at 05:35 PM.
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Old 03-01-2011, 05:14 PM
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Possibly, pixel rejection during calibration? This might be helpful. Not sure?

http://pixinsight.com/tutorials/master-frames/en.html
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Old 03-01-2011, 05:37 PM
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Possibly, pixel rejection during calibration? This might be helpful. Not sure?

http://pixinsight.com/tutorials/master-frames/en.html
AFAIK, that method is only useful for removing unwanted pixels; ie cosmic ray hits, star trails, etc.. though 3 lights and dark/bias calibration are required for a good sigma reject run. It wont help with dust motes.

You can always tidy them up in processing with a heal tool or clone stamp tool in photoshop.
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Old 03-01-2011, 05:50 PM
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In "The New CCD Astronomy" at Ch 6 (p. 239) it is suggested that the larger artifacts are probably from dust on the face of the camera, or on filters in front of the camera. An image is provided to illustrate.
Hope this helps.
Peter
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Old 03-01-2011, 06:22 PM
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Interesting, thanks the only thing is front of the ccd chip is a nose filter and it looks clean to me
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Old 03-01-2011, 06:42 PM
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Those dust motes of yours look like they are caused by the primary. Those small dark motes in Peters image are often from the ccd.
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Old 03-01-2011, 08:29 PM
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Dan what primary mirror are you referring to as I'm using a QHY8 OSC CCD camera
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Old 03-01-2011, 08:55 PM
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Dan what primary mirror are you referring to as I'm using a QHY8 OSC CCD camera
?

Dust on your scopes primary mirror.
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Old 03-01-2011, 09:32 PM
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Has to be really bad before it'll affect an image motes on a mirror won't show up in an image too removed from the focal point
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Old 03-01-2011, 10:00 PM
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Not quite sure what you're saying there?

Doesnt have to be really bad; just has to be present and depending how far you stretch your data the more noticable it will appear.
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Old 03-01-2011, 10:01 PM
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Originally Posted by leinad View Post
Those dust motes of yours look like they are caused by the primary. Those small dark motes in Peters image are often from the ccd.
I think they are too small to be on the primary mirror. It is probably on the nose filter but just too small to see. Here is a calculator to estimate the chip to dust distance: Dust Donut Calculator
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Old 03-01-2011, 10:13 PM
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The donut is a dust mote in the imaging train (not the camera or nosepiece tough, it's much farther) that wasn't flat fielded. The lines in your second shot are a read out artefact. Usually happens in warm weather. Check your master bias to see if it has the same lines. Otherwise it might be in one of your subs in the stack.

Last edited by multiweb; 03-01-2011 at 10:29 PM.
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Old 04-01-2011, 12:08 AM
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The donut is a dust mote in the imaging train (not the camera or nosepiece tough, it's much farther) that wasn't flat fielded.
You got me thinking with this post. I would have thought that at that size the dust would be fairly close to the CCD. I used the calculator I posted a link to to do some testing. I found that with my WO FLT110 and the QHY-9 camera for a dust donut that was as wide as the CCD sensor the dust would only be 62.861mm from the CCD. Am I not understanding something?
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Old 04-01-2011, 02:43 AM
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Could quite possibly be the clear filter on the QHY8 nosepiece. To see closely you'd need to check in good lighting or daylight.

See this link for similarities
http://old.astrodon.com/oldsite/LearningCurve.html

I used a bunch of cottonballs one at a time(not turning over to prevent finger oils getting on the swipe side) with mineral turps to wipe and dry out the clear filter window.

Now frosting is a real pain in the pants. I luckily one night had just the right humidity indoors to do a quick CCD clean and reassemble to use outside without further issues. When you see frosting you'll first think, Ooo pretty snowflakes... damnit!


Found a flat from the QHY8C, Im pretty sure at that time the many motes where from the primary mirror. At the time I had a focal reducer in that caused some curvature as you can see with the motes around the edges. I'm pretty sure the smaller dark mote at the bottom was dust spec on the nosepiece window. Goin from memory here
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Old 04-01-2011, 07:35 AM
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You got me thinking with this post. I would have thought that at that size the dust would be fairly close to the CCD. I used the calculator I posted a link to to do some testing. I found that with my WO FLT110 and the QHY-9 camera for a dust donut that was as wide as the CCD sensor the dust would only be 62.861mm from the CCD. Am I not understanding something?
No you're correct. It could be on the secondary or any corrector before the CCD but it's too close to be on the nosepiece or 55mm away (like a MPCC). Your 60mm+ sounds plausible given the size of the donut. On my newt that would correspond to that distance approx.
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