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14 Nov 2018
Glad to announce of release of INDI Library v1.7.5 on 2018-11-14. A few drivers were added in this release as we continue to improve & stabilize existing drivers.
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TOPIC: First time issues with automated focusing

First time issues with automated focusing 7 months 3 weeks ago #24551

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This is my first time using automatic focusing in EKOS. Typically, I focus once, then never touch it again, and I've not had issues with my flats. But my first imaging session, I did one full set of L at one focus setting, then switched to Red and focused again. I left the focus for G & B at the same setting. Then I did all my flats at my last focus setting, which was what RGB were set to.

If I don't take my flats at the proper focus, I would assume dust motes would not correct out of the image properly?

Hence, the below stretched Luminance image showing uncorrected dust motes.



And then this stretched Green showing no dust motes. Red and Blue also didn't have any.




If you are automating the process of capturing with refocus either for temperature changes or filter changes, then how do you account for the focus setting? Is this information saved somewhere in the image, or can it be appended to the file name?

Also, I took the flats at 20k ADU, which has been typical for me in the past, but as you can see vignetting wasn't fully uncorrected in these images. What's the best way to understand the proper ADU for your flats to correct properly?
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Re:First time issues with automated focusing 7 months 3 weeks ago #24552

I'm far from being an expert at this, but to me flats provide correction for dust/vignetting located on the optical path between lens and photosites. Thus focus shouldn't have any impact because that path is moving as a whole during that process, except for the the scattering of light over the sensor. But I can't see any reason to change the focus for flats neither. I suppose the type of optics would also make a difference, doublet or triplet refractors for instance. Still, I'm no expert at this.

-Eric

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First time issues with automated focusing 7 months 3 weeks ago #24553

I've actually had similar experience with the dust motes. I ended up shooting flats immediately after a filter capture is complete. Now that I think about it again... It might be a good idea to store the filter offset for each filter somewhere and then when flats for that filter are taken, the filter is moved to the position.... Ok I'll add this to my TODO list.

Regarding ADUs, I take it at 25k personally, some even suggest going higher. IMO, it's not an exact science as some might claim so it would take a bit of trial and error to see what works best for your optical train.

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Re:First time issues with automated focusing 7 months 3 weeks ago #24569

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TallFurryMan wrote: I'm far from being an expert at this, but to me flats provide correction for dust/vignetting located on the optical path between lens and photosites. Thus focus shouldn't have any impact because that path is moving as a whole during that process, except for the the scattering of light over the sensor. But I can't see any reason to change the focus for flats neither. I suppose the type of optics would also make a difference, doublet or triplet refractors for instance. Still, I'm no expert at this.

-Eric


You're right in that the focuser is moving all imaging gear as a whole. But it's distance from the objective, which you are shooting through, changes. Thus the focus of any object through the objective, or dust on the objective, changes relative to the distance from the focuser. That's my understanding anyway.

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First time issues with automated focusing 7 months 3 weeks ago #24570

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knro wrote: I've actually had similar experience with the dust motes. I ended up shooting flats immediately after a filter capture is complete. Now that I think about it again... It might be a good idea to store the filter offset for each filter somewhere and then when flats for that filter are taken, the filter is moved to the position.... Ok I'll add this to my TODO list.

Regarding ADUs, I take it at 25k personally, some even suggest going higher. IMO, it's not an exact science as some might claim so it would take a bit of trial and error to see what works best for your optical train.


What's the difference between storing the offset, versus the absolute position of the focuser on each filter? Would the absolute position be more accurate, if for instance you accidentally moved the focuser before you shot flats?

As someone who has to tear down the setup each night after shooting (and before I'm able to set the scope in front of a light box), knowing the absolute focus position would eliminate any guesswork if the focuser got bumped or moved when tearing down the setup. Obviously though, I try to avoid bumping it if at all possible, and leave my imaging train intact when moving the scope, but it doesn't rule out accidental bumps.

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