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Old 15-07-2020, 12:39 PM
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pkinchington (Peter (Kanga))
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Are these artifacts?

In my recent image of eta carinae 3rd try using an unmodified dslr I got an image after stacking and processing with dark 'holes'. Are these artifacts or a feature?
Cheers Kanga
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Old 15-07-2020, 12:41 PM
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multiweb (Marc)
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Yes. Probably spots or droplets in your imaging train.
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Old 15-07-2020, 01:05 PM
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Yes. Probably spots or droplets in your imaging train.
Thanks I think that is likely I felt a couple of drops of drizzle.
Cheers Kanga
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Old 15-07-2020, 01:25 PM
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It can help in narrowing down the culprit to know that the closer to the sensor the issue is, the smaller and more focused the dots will be. Are you using a filter? Could be dust on that.


Best,


Markus
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Old 15-07-2020, 03:01 PM
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As Markus said, the closer to the sensor the shadow is, the smaller it is.

This formula is useful for locating shadows and/or halo's.

Distance from sensor (mm) = (p x f x d)/1000

Where p = pixel size in microns
f = focal ratio
d = diameter of shadow/halo in pixels
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Old 15-07-2020, 06:59 PM
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pkinchington (Peter (Kanga))
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Quote:
Originally Posted by Stonius View Post
It can help in narrowing down the culprit to know that the closer to the sensor the issue is, the smaller and more focused the dots will be. Are you using a filter? Could be dust on that.


Best,


Markus
Hi Markus - I am not using a filter why I think it is not dust is that stars are within the areas I have pointed to.
Cheers Kanga
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Old 15-07-2020, 07:00 PM
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pkinchington (Peter (Kanga))
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Quote:
Originally Posted by billdan View Post
As Markus said, the closer to the sensor the shadow is, the smaller it is.

This formula is useful for locating shadows and/or halo's.

Distance from sensor (mm) = (p x f x d)/1000

Where p = pixel size in microns
f = focal ratio
d = diameter of shadow/halo in pixels

Thanks for the formula.
Cheers Kanga
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Old 16-07-2020, 09:05 AM
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They just look like dust spots to me, are you using a DSLR lens? It may be dust on the rear element of the lens. Though it looks like the main image might be out of focus too.

It is not unusual to still see stars in the shadows of dust motes. Try shooting some flats (Properly or not) and you will probably see the shadow of dust quite clearly. As a quick setup, just use the ISO setting you normally use on the camera, pointed at a white surface like a ceiling, start with the shortest exposure your camera will give and slowly work your way up until you start to see the image brighten a little, at that point you will probably be able to see the dust motes quite clearly.

To process them out of your actual image, proper flats (That test above is just a quick and rough way to prove they are dust spots) will generally get rid of them quite nicely. But you need to shoot new flats at least any time you remove the lens, or if any dust shows up that is not processing out, or really preferably, every time you shoot data and keep the flats with the data so you don't have to work out which flats for which lights six months down the track when you feel like having another go at processing.
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Old 19-07-2020, 11:59 AM
phomer (Paul)
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Quote:
Originally Posted by pkinchington View Post
In my recent image of eta carinae 3rd try using an unmodified dslr I got an image after stacking and processing with dark 'holes'. Are these artifacts or a feature?
Cheers Kanga
Kanga,


Consider using flats, they are not part of the nebula, which you can confirm by viewing other imagers results. I would also invest more time in getting accurate focus, challenging but the results will be worth it.


Paul
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