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.
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.
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.
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.
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
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
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.
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?
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
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.