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INDI Library v1.9.8 Released (29 Sep 2022)

Bi-monthly INDI Library released with new drivers and bug fixes.

New Bahtinov Mask Assistant Tool

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Hi AstroMuni,

Adding a graphical indicator if you are turning the focus knob the right way would be a nice feature.

The trend graph that is enabled when in automatic mode (after pressing the start capture button) has an similar function. You can see in the graph if your focus is increasing or decreasing. In the graph you can see if the focus trend is going in the right direction.

I noticed that the HFR will fluctuate around a certain value when you take multiple images without touching the focus knop. The value of the HFR can either increase or decrease slightly due to atmospheric conditions. This means that you need some more captures between each focus change to see if the turn on the focus knob improved your focus.
These variations make it difficult to show in a graphical indicator if your focus change went the correct way after just one or two captures.

That's why I use the automatic mode even when performing manual focus actions. The graph gives me a good indication if my focus is right and if I turn my focus knob the right way.

Implementing a graphical indicator based on a single measurement, might give misleading information, as it might happen that you turned the focus knob the right way, but due to atmospheric conditions, the HFR value stays the same or went the other way. Then the indicator will show that you should turn your focus knob the other way and you see in your next measurement that it got even worse.

But I will put my thinking cap on :-) and see if I can find a solution for that. I do agree that for manual focus such an indicator can be a good improvement.

Thanks for the feedback. Suggestions are always welcome.

Kind regards,
AstroRunner
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1 year 6 months ago #71644

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Perhaps you could compare it with whatver HFR value was showing just before the capture took place or take an average of the values (if its possible ofcourse) :-)
Another nice to have would be if there was some way to 'calibrate' it to understand if the focusser was moving in or out and then be more intelligent in suggesting what the user should do!

Celestron Astromaster 130 on HEQ5 Pro mount, ZWO ASI224mc, 30mm guidescope with ASI120mm mini. All managed using Kstars/Ekos on RPi with Astroberry build.
1 year 6 months ago #71647

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This is a very helpful thread about what must be a very helpful feature.
I am looking forward to using it as soon as I get a clear night.
8 months 3 weeks ago #81218

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Hi AstroRunner,
I have a question about the HFR when a Bahtinov mask is in place. Is that accurate or does the mask 'spoil' the view and HFR readings become less meaningful? i.e all that matters is how close is the centre line to the actual centre.

Celestron Astromaster 130 on HEQ5 Pro mount, ZWO ASI224mc, 30mm guidescope with ASI120mm mini. All managed using Kstars/Ekos on RPi with Astroberry build.
Last edit: 3 months 3 weeks ago by AstroMuni.
3 months 3 weeks ago #85222

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Hello Astromuni,
I am not sure to be the right person to answer. Otherwise, in my opinion, HFR with Bahtinov might be of poor help.
Maybe some people using this function can answer in a better way.
Clear skies
3 months 3 weeks ago #85223

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Didnt realise there were 2 Patricks in this conversation :-) I was hoping Astrorunner would respond.

Celestron Astromaster 130 on HEQ5 Pro mount, ZWO ASI224mc, 30mm guidescope with ASI120mm mini. All managed using Kstars/Ekos on RPi with Astroberry build.
3 months 3 weeks ago #85224

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The Bahtinov mask produces a strongly diffracted star image, for which something like a HFR doesn't make much sense. If you use such a mask for focus, look only at the position of the line. Reported HFR values are meaningless.

EDIT: This referred to HFR as what it actually means. I wasn't aware that the assistant calls the offset distance "HFR" - my bad :(
openSUSE Tumbleweed KStars git INDI git
GPDX+EQMOD, CEM60EC, ASI2600/1600/290mini+EFW+EAF
Last edit: 3 months 3 weeks ago by Peter Sütterlin.
3 months 3 weeks ago #85232

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Hi AstroMuni,

The HFR does not represent the same as with the other focus methods. But the HFR is not meaningless. The HFR in the Bahtinov mask focus assistant is a value that represents the offset to optimum focus. This means that the closer this value is to 0, the better you are in focus, where 0 represents perfect focus. Unfortunately the HFR value used for the Bahtinov focus assistant does not have a unit, that will make predicting how much you need to move the focus to get perfect focus difficult. Example: You can NOT say for instance that when the HFR value for Bahtinov focus is 1.2 the you need to move your focuser a certain amount of micrometer to get to perfect focus.
I think just like with the other auto-focus methods, a scan is done from one focus position to another to create a curve, then the lowest point in that curve is the optimal focus position. The same works for the Bahtinov auto-focus too.

I hope this will answer your question sufficiently.

Kind regards,
AstroRunner
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3 months 3 weeks ago #85261

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In effect you are saying that when I select the Bahtinov mask option, the graph is NOT showing HFR but a representation of the offset, right?

Celestron Astromaster 130 on HEQ5 Pro mount, ZWO ASI224mc, 30mm guidescope with ASI120mm mini. All managed using Kstars/Ekos on RPi with Astroberry build.
Last edit: 3 months 3 weeks ago by AstroMuni.
3 months 3 weeks ago #85262

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Hi AstroMuni,

Yes, that's right. For the Bahtinov focus the HFR labels should actually say something like "Offset". That would have been less confusing.

Regards, AstroRunner.
3 months 3 weeks ago #85268

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I am using Kstars 3.6.0 on Linux Mint and I get this pattern when I choose the Bahtinov mask option. What do all these numbers mean? And what am I doing wrong. I thought once I select the star I should start seeing 3 lines and an offset reading for central line.

Celestron Astromaster 130 on HEQ5 Pro mount, ZWO ASI224mc, 30mm guidescope with ASI120mm mini. All managed using Kstars/Ekos on RPi with Astroberry build.
Last edit: 3 months 3 weeks ago by AstroMuni.
3 months 3 weeks ago #85289
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Hi AstroMuni,
I would expect that after you selected a star in the image, it would capture the image again and then indeed show the 3 lines. From your question I understand that has not been the case. You can try to click the capture button again to force taking a new image and make the Bahtinov calculation. If it still fails, can you look at the log messages at the bottom of the window to see if there is an error?
I haven't been able to check Kstars version 3.6.0 for myself yet. But I will give it a try as soon as I have more time for it.
Regards, AstroRunner
3 months 3 weeks ago #85297

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