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rnobleeddy

Any idea what causes this smudge on my images?

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I have a 130PDS, fully modded Canon 450D, Bader MPCC and astronomik CLS CCD clip in filter. I've started to see the following pattern on my lights - highlighted in red below on a flat. Initially thought it be a hair or a streak of dried residue, but I'm struggling to locate it.

At least some of is making it through to to the stacked image (albeit only visible when fully stretched). I take plenty of flats, generally using  a laptop screen and white cloth. I'm dithering but maybe don't dither far enough, and I probably haven't had enough images to stack in recent attempts (usually 20x5min subs). I'm not using darks.

I do not see any hint of this when I use the 450D (plus CLS CCD filter) with a lens, so I guess it must be related to the scope or coma corrector. The coma corrector glass, primary and secondary look pretty clean except for what I think is a usual amount of dust dust.

It's always in the same position on the image regardless of camera rotation.

image.thumb.png.249063fdc5a6db0e1c18765089b2d0eb.png

 

Hoping that someone with more experience could let me know what this might be - the size and the fact it's invariant to rotation would (in my opinion) rule out the optical train of the telescope, but then I don't understand why I don't see it with a lens?

 

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5 hours ago, rnobleeddy said:

I have a 130PDS, fully modded Canon 450D, Bader MPCC and astronomik CLS CCD clip in filter. I've started to see the following pattern on my lights - highlighted in red below on a flat. Initially thought it be a hair or a streak of dried residue, but I'm struggling to locate it.

At least some of is making it through to to the stacked image (albeit only visible when fully stretched). I take plenty of flats, generally using  a laptop screen and white cloth. I'm dithering but maybe don't dither far enough, and I probably haven't had enough images to stack in recent attempts (usually 20x5min subs). I'm not using darks.

I do not see any hint of this when I use the 450D (plus CLS CCD filter) with a lens, so I guess it must be related to the scope or coma corrector. The coma corrector glass, primary and secondary look pretty clean except for what I think is a usual amount of dust dust.

It's always in the same position on the image regardless of camera rotation.


Hoping that someone with more experience could let me know what this might be - the size and the fact it's invariant to rotation would (in my opinion) rule out the optical train of the telescope, but then I don't understand why I don't see it with a lens?

 

This tells it is on or just in front of the sensor of your camera or on your clip-in filter
It may be a very thin hair. The shape and the fact that is seems to be a bit darker at the sides, giving it a tube-like appearance points in that direction.
Inspecting your sensor (and clip-in) with a magnifying glass, could show you the cause.

Edited by Waldemar

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Yes it looks like a hair on the sensor to me too. I had one appear on my 400D and had to set the camera to hold up the mirror then opened the shutter. Then  I saw it clearly in view. I blow with a can of compressed air dislodged it.

Edited by TerryMcK

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A rocket blower is a very useful tool to have. Compressed air cans aren't just air so aren't as safe as a rocket blower (rubber bulb you squeeze with hand) which is just air.

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10 hours ago, Waldemar said:

This tells it is on or just in front of the sensor of your camera or on your clip-in filter
It may be a very thin hair. The shape and the fact that is seems to be a bit darker at the sides, giving it a tube-like appearance points in that direction.
Inspecting your sensor (and clip-in) with a magnifying glass, could show you the cause.

 

7 hours ago, TerryMcK said:

Yes it looks like a hair on the sensor to me too. I had one appear on my 400D and had to set the camera to hold up the mirror then opened the shutter. Then  I saw it clearly in view. I blow with a can of compressed air dislodged it.

Thanks - is there any reason why I wouldn't see it with a lens? In fairness, it may just be that I can't see it on the camera screen. I will check the lens flats when stretched too. 

I happen to have some compressed air handy as I needed it for something complete different, so I'll do some more searching!

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using compressed air is quite tricky!! First of all it is not just air and second if you move it while spraying, liquid may come out. Be very careful.
Better use a rocket blower as mentioned before.

The camera screen has a low resolution, hard to see anything beyond an impression.

Edited by Waldemar

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I have something very similar looking on my 60Da along with a few dust bunnies. I've left it as after using Darks, Flats and Bias it doesn't show in my images. 

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If you inspect the sensor, do so under a very bight light... better, a headtorch set to full power - that will show up pretty much anything that shouldnt be there.

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Thanks all. There was a hair on the sensor. I used the compressed air this time, but will get a blower for next time. Unexpectedly clear  tonight so will see if it worked!

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