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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

Tips for Auto-Focus

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Replied by Mark Aston on topic Tips for Auto-Focus

Thanks Peter, too big a step size has been my playground for a while, but I’m only using 10 and 15 steps at present. I can see the star image grow and shrink nicely, but it’s EKOS that does not seem to stop before it goes so far as to produce annuli. I don’t get this at all and it’s going past a x3 HRF.

I will keep playing, but one thought that is coming to mind is that the iOptron focuser is not up to the job…

Cheers

Mark
1 year 4 months ago #88210

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Replied by Nigel Dunmore on topic Tips for Auto-Focus

Try setting the max travel to restrict how far it moves from its initial start point.

I’ve been trying to find how to handle donuts with my C6 when it moves even a 100 steps from its focus point and this seems to at least stop the algorithm wandering off. Unfortunately not sure, at least in my case, whether this will stop me getting a V to identify the new focus point.
1 year 4 months ago #88213

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Replied by Peter Kennett on topic Tips for Auto-Focus

As Nigel says, your “max travel” is set too high.
1 year 4 months ago #88214

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Replied by Nigel Dunmore on topic Tips for Auto-Focus

Hi Peter

I was just looking at your settings and thinking the sizes were huge, then I checked the lightcrawler steps per revolution - 374920 so rather larger than my Celestron focus motor which has 1000.

I thought my max travel of around 100 was small (nb still waiting for a clear night to try my settings out properly) at 36 degrees of rotation but yours seems to be around 2 degrees. Am I missing something because that would seem to mean it’s really hard to manually focus as just a tiny twitch would be 2 degrees?

Regards

Nigel
1 year 4 months ago #88215

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Replied by Mark Aston on topic Tips for Auto-Focus

Thanks Nigel and Peter, max travel is probably the culprit as you say, but based on experience of other autofocus programmes, I was expecting EKOS to determine a limit of increasing size itself to decide whether to focus in or out, to auto v-curve the action.

Is there a description of the algorithms employed in the various measurement options so I can see how the main variables the user inputs will affect the operation of the system?

All the best

Mark
1 year 4 months ago #88216

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Replied by Peter Kennett on topic Tips for Auto-Focus

Yes, the Litecrawler has extremely fine steps, for long focal length scopes. While I don’t manually focus at all, it has a dial to adjust the step size increment so you can move the focuser quickly if needed.
1 year 4 months ago #88217

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Replied by Peter Kennett on topic Tips for Auto-Focus

I’m a little confused at to what you referring to when you say “degrees”. I am not using the normal C11 focuser. The Litecrawler sits in the optical train and has its own focuser and rotator.
1 year 4 months ago #88218

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Replied by Peter Kennett on topic Tips for Auto-Focus

Here's some help that shows the relationship between the initial step size, max step size, and max travel. The goal is to get a nice curve. I can get a good curve with just 3 steps outward and inward. I have used more but it didn't improve anything.

You need to know how many steps YOUR focuser needs to go from an ideal HFR (smallest value obtainable) to 2 times that number.
This is first done by moving the focuser in small amounts and manually capturing images and noting the HFR values. Once you know how many focuser steps you need to double the HFR - the rest is easy.



This is how I set mine up, There may be other ways or methods - but this technique works VERY well for my setup. Obviously your actual values will be different, but the technique should work.
The following user(s) said Thank You: Stefan, Rafael Schlegel
1 year 4 months ago #88221
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Replied by Nigel Dunmore on topic Tips for Auto-Focus

By degrees I was meaning how much you rotated the knob on the telescope. I was thinking you were using the standard focuser knob on you C11 like I do on my C6 but it looks like I’m mistaken.
1 year 4 months ago #88224

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Replied by John on topic Tips for Auto-Focus

Thx for the tips Peter, I'm sure people will find this very helpful.

I'm wondering if the 2x HFR "rule" that you use to setup focus would be more generally applicable to SCTs. If so, I can update the focus documentation. It would be interesting to hear your comments Nigel as you and Peter almost bookend the size range of generally available SCTs.

(Small point but just FYI, Linear and Linear 1 Pass don't use Max Step Size).
1 year 4 months ago #88225

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Replied by Peter Kennett on topic Tips for Auto-Focus

No I don’t use the built-in mirror focus. It leaves the mirror unstable and allows mirror flop. Also, it causes image shift while focusing. I’m at such a long focal length that neither effects are acceptable to me. The Moonlite Litecrawler allows me to keep my mirror locked down tight. In addition to focus it also gives me automatic rotation, perfect for remote control use.
1 year 4 months ago #88226

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Replied by Peter Kennett on topic Tips for Auto-Focus

Thanks John, I had a feeling I wasn't seeing any changes with the Max Step Size. It wasn't greyed out, so I wasn't sure.
I think my 2X rule is for long focal length scopes - such as an SCT with an OAG. I am imaging at either 0.8 or 0.4 arc seconds per pixel, and so small changes in HFR are noticeable.
1 year 4 months ago #88229

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