Nigel Dunmore replied to the topic 'Tips for Auto-Focus' in the forum. yesterday

Have now been trying different SEP settings and have altered ‘min cont.’ to 0.1 from 0.005 that’s in the default setup. This seems to make the algorithm pick out the donuts better. More testing obviously needed.

YMMV …..

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Nigel Dunmore replied to the topic 'Focus backlash issue' in the forum. yesterday

ok this is just an idea based on a theory based on reading various websites… so may be completely stupid….

In the C6 manual when it goes on about how to focus, it says to go counter clockwise as the last step (ie lifting the mirror). Then when you have got your target in sharp focus (I’m sort of assuming the target is in the middle here as I’ve not got the manual to hand) to give it an extra turn of 1/12th of a turn for visual use and 1/24th of a turn for photographic use.

What I believe the idea is, is that given the sensor is a flat plane but the image focus point is in a curve with the edges further ‘in’ , that moving it a bit further moves the central part towards the back of the cfz and in doing so brings more of the edge into it.

For my setup C6 with a Celestron focuser we are on about approx 30 microns or 40 steps. This sort of matches somethings I’ve read (specifically the article from sky and telescope in 2010 by Don Goldman and Barry Megdal - In perfect focus - link astrodonimaging.com/tutorials/ ) the cfz for an f/10 is around 40 micron and f/7 around 20 micron in one direction (so I assume 40 and 40 wide).

So once in focus on the target in the middle of the image a step out of 40 would bring more into the cfz.

Possibly this is a bit of a old idea and that doing the focusing using the whole or large part of the frame makes it irrelevant.

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Nigel Dunmore replied to the topic 'Focus backlash issue' in the forum. 2 days ago

CFZ - don’t suppose you are working on some way of putting the central focus area towards the back of the cfz so those who either don’t have flatteners or whose flatteners don’t quite work have more of their image in the cfz? Or is that a daft thing?

How are you working out the cfz? I’ve seen different ideas for working this out which for my setup seem to range from over 150 microns down to 20.

Regards

Nigel

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Nigel Dunmore replied to the topic 'Focus backlash issue' in the forum. 2 days ago

What is this overscan thing? Is it just backlash compensation implemented in the lp1 algorithm? Wouldn’t that be the same as breaking the link between the current backlash entry and any driver backlash? What about the other algorithms? Isn’t there a way to implement backlash compensation somewhere between the algorithms and driver? If that was done all focusers would have bc even if their indi driver didn’t implement any and it would work for all algorithms. People whose focuser drivers had a more sophisticated/specific bc setup could use that and switch off this one.

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Nigel Dunmore replied to the topic 'Focus backlash issue' in the forum. 3 days ago

Let’s split things down a bit.

1. You have the algorithms - they take a set of data and work out where the optimal focus point is. The data could be a set of images plus focuser position or something like the current temperature and some preprocessed info for it to work out where the focus point is.

2. Backlash - this occurs afaik on change of direction of the focuser mechanism. Simplest solution appears to be to overshoot by some amount greater than the max backlash then move to the real position. It doesn’t really matter if the backlash varies each time or in either direction as long as the overshoot is greater. (I’ve no idea why NINA looks to have settings for both - this could just be the gui misleading me and only one is actually used).

3. Final move direction - in the case of sct’s with a focuser moving the mirror final the move direction needs to be against gravity. This move would also need to apply backlash compensation if it was a change of direction.

Current setup seems to not be quite right as it different parts seem to try and solve problems of other parts. I think the link between the backlash setting in the main gui needs splitting off from the focuser indi driver. Then the backlash compensation done independently of the algorithms and drivers if wanted by the user. The algorithms shouldn’t have anything to do with backlash. The indi driver could implement some focuser specific compensation if needed. The final move direction I think would be in the driver and would be active on every move that’s not in the ideal direction. This would shield the algorithms from bad positions without them having to know about it.

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Nigel Dunmore replied to the topic 'Focus backlash issue' in the forum. 4 days ago

ok the relevant code looks to be :-
——-
// implement backlash
int delta = targetTicks - FocusAbsPosN[0].value;
if ((FocusBacklashN[0].value < 0 && delta > 0) ||
(FocusBacklashN[0].value > 0 && delta < 0))
{
backlashMove = true;
finalPosition = position;
position -= FocusBacklashN[0].value;
}

if (!startMove(position))
return IPS_ALERT;

———
so the answer looks to be yes. If it’s moving inwards - delta <0 and focusBacklash is positive then it will subtract the backlash ie move further inwards, then later in another bit of code move outwards to the final position. This occurs for both absolute and relative moves. Doesn’t seem to worry about whether this is a change of direction or not which in this case is for the good.No idea why it would want to have backlash compensation in the other direction but the code seems to allow that.

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Nigel Dunmore replied to the topic 'Focus backlash issue' in the forum. 4 days ago

Looks like I was misunderstanding NINA.

The relevant page is nighttime-imaging.eu/docs/master/site/advanced/autofocus/

They have two types of compensation.

1.Absolute where it adds on a set of steps at a change of direction - looks to require knowing quite accurately your backlash. Not sure if this can have different numbers of steps for in and out as it doesn’t say but the gui having both seems to point to a possibility.

2. Overshoot which moves past the point then back to it. This has either in or out steps set but only one. This is so the focuser always completes its movement in one direction.


There’s a tip later in the manual - “ Overshoot can be very useful for SCT users to avoid mirror flop. In fact, when setting the Backlash Compensation to IN, the last focuser movement will always be outwards.”. Looks like NINA uses this rather than a switch like I was suggesting. I suppose the extra back and forthing is of little consequence just doesn’t seem tidy to me.

Now time for me to check whether the Celestron sct does the backlash compensation wiggle each move or not..

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Nigel Dunmore replied to the topic 'Focus backlash issue' in the forum. 4 days ago

My two pence worth…

surely it would be better to split off the backlash settings from the actual focusing algorithms given they are more to do with the focuser mechanics than how you work out how to do a curve to determine the best focal point?

Also looking at NINA that seems to have an idea of both in and out backlash compensation. Not sure whether you use both or just one. Which also brings me to in/out direction and sct’s, I’ve yet to try this out at night, but it looks like working in the in direction drops the mirror when really want it to be raising it. Maybe a switch would be of use for that, again maybe as part of the focuser mechanics.

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Ok turns out to be sort of user error doh..

While setting up my focuser I had got the feeling that there was some sort of usb port clash and while trying to prevent that I had somehow ended up with it thinking it had no port. This for some reason causes the driver to crash taking kstars with it. It also means it doesn’t display the indi control panel making it hard to see what might be the problem.

Hacking the config xml enabled the debug logging and I eventually got a log file with the clue as to my having null as the port. Removing the entry in the profile and then adding it back resolved the problem and everything is now starting.

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Not entirely sure. I try and start ekos/indi via kstars and kstars crashes. Try kstars again and it is able to connect to the now running instance but the driver for the mount fails to start. Got to do some digging around in log files to try and work out what’s upset it.

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btw I’m on about changes in the last couple of weeks. It was working very recently.

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Hi

I’ve updated my astroberry to the latest release (as of the 18/11/22 not got the versions to hand) and now I’m unable to get my iexos-100 mount to connect. In fact when I try and start my ekos profile kstars just crashes. On next attempt it seems the indi server is running and I can connect to it but the mount doesn’t appear in the indi screens. If I try restarting it kstars crashes again.

Anyone else having problems with the latest software versions (kstars is still at 3.6.0 because astroberry is still 32 bit so thatshould be a stable build so it looks to be something else..)? A bit of a long shot just don’t want to spend hours poking around if it’s not actually just my specific setup.


Thanks

Nigel

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With mine when it platesolves it works out what the real focal length is and updates the setting - the figure in brackets. At least it did, I’ve just updated my astroberry and now I cannot even get my mount working with kstars just crashing out when I try and start ekos…

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Nigel Dunmore replied to the topic 'Tips for Auto-Focus' in the forum. 1 week ago

Hi Mark,

Peter etal have more experience of this than me as I’ve only just got a focuser so you might want to take what I say with a pinch of salt….

The way I see it you need to move far enough from focus to get hfr’s that produce a V. Peters said how he does it and from his graph he gets a nice V. Me with my simpler equipment I’ve yet to get a proper V but I am developing an understanding of how this works now so maybe I will come up with an initial steps setting etc which works.
However I suspect that to get enough of a change in hfr I will stray into donut territory which leads to problems. Now I believe to handle those I need to pick/tweak the appropriate SEP settings. To do that I’m aiming to take some images that are out of focus to see what helps count the whole donut rather than just little bits. I’ve tried reading the ‘do not panic’ guide to SEP but obviously that’s for phd level people so I’m going to have to do some poking until I get an idea…unless of course someone else has already worked it out.


Regards

Nigel

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