Hey
I am trying to get better at controlling tilt and backfocus. I am working with my Octopi.
Have you ever seen the numbers in the Arberration inspector jump around like this?
I am NOT making any changes between these runs - and the numbers are ALL over the place.
Any input or advice?
I suspect that even very little wind might cause this.
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I believe the randomness gets worse with fewer stars. AI needs a dense star field in all corners as well as the center. It will run with few, but I think (based on observation not knowledge) that it gives less consistent results as the number of stars get less. I do not know if that is your problem, but I do know it works better as you get more stars; try finding a really dense area and/or lengthen your exposures.
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Is this without any changes, or after making a minor change. If you make a tilt/back focus change the numbers will vary a lot as focus is also affected, so you need to refocus and that's not always exact depending on the seeing conditions in my experience. Even things like temperature changes can affect these numbers over time.
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Hi Christian,
yes my results looks like yours. I think another reason depends on the differnent seeing conditions from one moment to another.
I haven't managed to adjust my optics perfectly with this tool yet.
Also, the best time for this is winter. And then you should move the telescope to one of the star-rich Milky Way regions to have much more stars.
CS
Kevin
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Michael Gorman:
Is this without any changes, or after making a minor change. If you make a tilt/back focus change the numbers will vary a lot as focus is also affected, so you need to refocus and that's not always exact depending on the seeing conditions in my experience. Even things like temperature changes can affect these numbers over time.
@Michael Gorman This is without making ANY changes AT all.
Literally just running the tool multiple times in a row.
I did make 1 autofocus run between 2 and 3 - that's the only this I did.
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Kevin Dahmke:
Hi Christian,
yes my results looks like yours. I think another reason depends on the differnent seeing conditions from one moment to another.
I haven't managed to adjust my optics perfectly with this tool yet.
Also, the best time for this is winter. And then you should move the telescope to one of the star-rich Milky Way regions to have much more stars.
CS
Kevin
@Kevin Dahmke Why winter?
I get the dense starfield - currently I'm on the Coma Cluster - which is less dense with stars.
That might be part of the reason.
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Linwood Ferguson:
I believe the randomness gets worse with fewer stars. AI needs a dense star field in all corners as well as the center. It will run with few, but I think (based on observation not knowledge) that it gives less consistent results as the number of stars get less. I do not know if that is your problem, but I do know it works better as you get more stars; try finding a really dense area and/or lengthen your exposures.
@Linwood Ferguson Will try that, thx!
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Christian Bennich:
@Kevin Dahmke Why winter?
I get the dense starfield - currently I'm on the Coma Cluster - which is less dense with stars.
That might be part of the reason.
Because now we can look out into the deep space.
As you say, you can see a lot of galaxies at the moment.
In the Winter monthes we can see the Milkyway arm at night sky with Tons of Stars in it.
That makes it easyer to finde a homogen Star field.
For Sure, in other monthes it's also possible but more difficult to finde a good starfield.
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all the questions:
What is your exposure length for the aberration inspector autofocus run?
How about for your regular autofocus/Hocus Focus run?
Do you have any compression fittings in your image train or all threaded connections?
When you run multiple autofocus runs (not aberration inspector) does the focus point keep arriving at the same focus step location?
Was your seeing poor/telescope still cooling down?
Apologies, to answer your question, no, I have not seen it jump around like that with no adjustments.... not that much anyway
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all the questions:
What is your exposure length for the aberration inspector autofocus run?
How about for your regular autofocus/Hocus Focus run?
Do you have any compression fittings in your image train or all threaded connections?
When you run multiple autofocus runs (not aberration inspector) does the focus point keep arriving at the same focus step location?
Was your seeing poor/telescope still cooling down?
Apologies, to answer your question, no, I have not seen it jump around like that with no adjustments.... not that much anyway
@noon - good and relevant questions, thank you for that.
Everything is screwed together. No compression fittings.
My autofocus is consistent, within a small margin.
The telescope “live” outside, so I assume it’s at ambient temperature and whether seeing was bad is hard to say. Most likely it was not super great.
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As a data point, (and contrary to my comment yesterday) I am just suddenly seeing similar things I’m not sure if it is user error or seeing-related. My aberration inspector last night would fail multiple times in a row and then suddenly succeed with a +-15micron tilt and no other changes. Sorry wish I had more to offer.
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Christian Bennich:
Hey
I am trying to get better at controlling tilt and backfocus. I am working with my Octopi.
Have you ever seen the numbers in the Arberration inspector jump around like this?
I am NOT making any changes between these runs - and the numbers are ALL over the place.
Any input or advice?
I suspect that even very little wind might cause this.
My suggestion is to use whatever method you like (in your case, aberration inspector) to minimize tilt and to then check it with a Bahtinov mask. Point your scope at a large open cluster with a lot of relatively bright stars and shoot a few 30s - 45s exposures with the B-mask on the scope. Then zoom in to examine the patterns over the whole field. If all of the patterns are perfectly symmetrical into all of the corners, you are done and you can stop adjusting things. The B-mask test is quick, easy, and unambiguous. Using a "long-ish" exposure averages out seeing effects so that you can pretty easily tell whether stars are in or out of focus. This isn't only a good way to cross check your results. I've used this method as the primary way to shim out tilt on the camera on my system in Chile.
John
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John Hayes:
Christian Bennich:
Hey
I am trying to get better at controlling tilt and backfocus. I am working with my Octopi.
Have you ever seen the numbers in the Arberration inspector jump around like this?
I am NOT making any changes between these runs - and the numbers are ALL over the place.
Any input or advice?
I suspect that even very little wind might cause this.
My suggestion is to use whatever method you like (in your case, aberration inspector) to minimize tilt and to then check it with a Bahtinov mask. Point your scope at a large open cluster with a lot of relatively bright stars and shoot a few 30s - 45s exposures with the B-mask on the scope. Then zoom in to examine the patterns over the whole field. If all of the patterns are perfectly symmetrical into all of the corners, you are done and you can stop adjusting things. The B-mask test is quick, easy, and unambiguous. Using a "long-ish" exposure averages out seeing effects so that you can pretty easily tell whether stars are in or out of focus. This isn't only a good way to cross check your results. I've used this method as the primary way to shim out tilt on the camera on my system in Chile.
John
Hi John
Great advice - I will definitely try that.
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As a data point, (and contrary to my comment yesterday) I am just suddenly seeing similar things I’m not sure if it is user error or seeing-related. My aberration inspector last night would fail multiple times in a row and then suddenly succeed with a +-15micron tilt and no other changes. Sorry wish I had more to offer.
It must be the Northern Hemisphere summer poltergeists playing tricks on us 🤣🤣
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