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INDI Library v1.9.8 Released (Yesterday)

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

Tips for Auto-Focus

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Replied by S on topic Tips for Auto-Focus


The linear focusing algorithm does an initial pass to get a V-curve using the initial step size and then it does a second (or more I guess) pass with half that step size. If you set it too big with the linear algorithm it does not reach focus very accurately, no matter which tolerance you have. So it never goes below half the initial step size and really need to be very fine tuned to work well. That is my understanding and experience at least...
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Last edit: 1 year 6 months ago by S.
1 year 6 months ago #68437

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Replied by Doug S on topic Tips for Auto-Focus

This is why I don't like the algorithm's completion logic. If you're not careful about setting the step size to within 1 CFZ, that last pass at 1/2 stepsize will put you at a focus that is a bit too coarse (or possibly even out of the CFZ!). For those who will eventually use AFC, it means that this relative offset from best focus will be "frozen" as you adjust along the temperature sensitivity curve. Much better to set that last position to the polynomial minimum (as long as it's still inward from the tolerance zone). That keeps the backlash portion of the algorithm design decision in place, but honors the work of all HFR readings in creating the V curve in the first place. There are lots of unknowns involved while focusing, but your best last focus position should be the minimum of all those measurements taken (IMO). That sets you up for a nice ride on the temperature curve. ;-)
RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.
1 year 6 months ago #68441

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Replied by S on topic Tips for Auto-Focus

With all the noise in a sigle hfr measurement, I would also rely on the quadratic model. Maybe you can suggest it as an option?
Last edit: 1 year 6 months ago by S.
1 year 6 months ago #68442

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Replied by Doug S on topic Tips for Auto-Focus

Done....but minds change slowly about these kinds of things. Not everyone appreciates the power of averages and curvefits over single measurements..... ;-)
RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.
1 year 6 months ago #68444

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Replied by Rishi Garrod on topic Tips for Auto-Focus

What magnitude stars do you typically choose?
I assume this is also dependant on the filters in use.
I tend to go for magnitude 3 or 4 stars?
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1 year 6 months ago #68445

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Replied by Miguel on topic Tips for Auto-Focus

the more I read, the less I know!
Well, I'm starting to understand how autofocus works under the hood. But, as a good newbie, I have some basic questions. There are some settings I don't get the point completely. For example, what annulus setting means? Yes, I can read the tips ekos shows up, but don't really understand. Could please anybody clarify?
1 year 6 months ago #68448

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Replied by Andrew on topic Tips for Auto-Focus

Mgutierrez:
The annulus' are used to define areas of exclusion where stars will not be selected for measurements. This is to avoid measuring something nebulous in the center of the frame, and possibly distorted stars on the periphery of the image.
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1 year 6 months ago #68454

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Replied by Miguel on topic Tips for Auto-Focus


Thanks for the reply; yes, I know that. But I'm not sure what defines exactly the threshold you can set. The annulus ekos tooltips talk about "[...]the percentage of the frame that are filtered out[...]". But this options is only present when selecting "Full field" checkbox; so, "the percentage of the frame", which frame? the whole frame? if so, how is related with the annulus? Basically, I don't understand what that threshold defines
1 year 6 months ago #68459

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Replied by Andrew on topic Tips for Auto-Focus

It is the percentage of one side of the full image frame. For example with an image frame of 1000x1000, excluding 10% from the center will be a circle 100px wide where stars are not measured. Out to the edges of the frame, including 90% will be a circle 900px wide, and anything outside is excluded.
INDI/KStars on Raspberry Pi 4, 4gb
Raspbian Buster with AstroPi3 script configuration
Skywatcher HEQ5 Pro Mount
Canon 600D Camera
Orion SSAG/ASI120mm @280mm Guide Scope
PHD2
Waveshare Stepper Motor Board - DIY Focuser
Adafruit GPS Module
Generic Bluetooth Joystick.
Startech 7 port powered USB Hub.
The following user(s) said Thank You: Miguel
1 year 6 months ago #68496

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Replied by Miguel on topic Tips for Auto-Focus

Thanks for the reply. In fact in supposed something like that. But the word "annulus" was confusing to me. I thought that should be related to star annulus, which did not make sense; hence the confusion. Now even I can see more clear; now that I'm able to see the circles in the graph. I'm just trying now my new focuser. Before I was playing with simulators.

Thanks!
1 year 6 months ago #68498

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Replied by Eric on topic Re:Tips for Auto-Focus


Yes, trying out focusing with the simulators is currently not very helpful. I hope to change that before the end of the week.


-Eric
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1 year 6 months ago #68510

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Replied by Eric on topic Re:Tips for Auto-Focus

For reference, my PR updating the flux calculation in the CCD Simulator was merged in indilib. That should make the Focus simulation a bit more realistic.

-Eric
HEQ5-Pro - Atik 314E - Orion ED80T - DMK21 on Orion 50mm
DIY 3D-printed Moonlite and FWheel RGB/LPR
KStars and indiserver on two Atom 1.6GHz 1GB RAM Linux, VPN remote access
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1 year 6 months ago #68591

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