I've been imaging successfully with EKOS for a few years. I continue to occasionally come across an issue where the focus module picks up on some stray element, and gets way out of focus unable to recover. Unfortunately, it thinks it's in focus as it has no way of actually knowing. Last night, imaging M106, it did exactly this. After a dozen or so successful focus attempts, on one focusing run, it got out of focus and stayed there. Then the scheduler tried to check alignment, and the scheduler tried to solve the unfocused image 196 times. It seems at some point, the system should recheck focus with so many failed attempts. Looking at the focus parameters I noticed Max Travel, and Max Step size. Which of these would I want to set to stop this from happening? Usually focus seems to float within a few hundred (0-250) or so. I have a Moonlite focuser, so no backlash, and I've been using Polynomial process.

What should my parameters be for both the process and mechanics tab. Thanks for any help. I've lived with this issue far too long, and probably could have avoided it had I looked closely at these settings.

Instead of Gradient Detection you may wanna try SEP. That very often gives me excellent results. Also try a smaller initial step size. This will ensure that the focuser doesn’t take big jumps though it also requires a close to optimum initial focus so you may need to manually focus (more or less) before switching to auto focus. And a tolerance of 1% is too small. Better try 5%. Finally I average over 3 frames to reduce the effect of varying seeing.

Do you try to focus with a single star, sub frame or entire FOV? I switched to entire FOV using an inner annulus of 25% and an outer annulus of 80%.


HTH, Wouter

What does tolerance actually do? I've tried full frame focus, but find that the overall FWHM is larger (maybe that's because it's averaging it across the frame). I do single star, auto selection, subframe. I will definitely set average. And a smaller initial step size. Though since focus varies as much as 200 on my Edge scope due to temperature drops, I don't think I want to make it too small. I'm thinking max step size and max travel are probably wrong and I still need to set them. I believe either or both have something to do with how far focus is allowed to travel before resetting. And since they are large, it allows my scope to get far out of focus without resetting. I just don't know which I should adjust and what they specifically have an effect on.

Not that I've been having any real troubles... I want to try your settings Wouter.

But you have a good point, I think it's very important to get into focus as close as you can manually before using the automation.

That step size should be 'just' large enough to produce a clear focus change so that the algorithm can decide in which direction it should look for the focus. After that, the polynomial algo will anyhow compute its own step sizes.
I can second the suggestion to use SEP and full field, this (now) seems to work very stable. I'm also using it.

I have to admit, I'm also unsure about the max step size and max travel, ISTR that max travel was the (integrated absolute) steps it does during the whole process, to prevent it continuously oscillates. The max single step size you should be able to cut down to maybe 500-700 at max if you typical focus variation is 200 steps.

Sorry about your issues.

In general, I agree with Wouter's recommendations. In particular:
- SEP detection
- Full field star detection with an inner annulus of 25% and an outer annulus of 80%
- For the moonlight v2 controller on my 4" refractor, I use a step size of 25
- 5% tolerance
- If you find the focus goes far away sometimes, you can constrain it with maximum travel. E.g. give it some freedom, but if, e.g. it should never travel 300 steps away, then use 300. For those without such issues, it's OK to leave that very large.
- I'm not as much a fan of multiple exposures if you're already doing full field, but, of course, feel free to experiment.
- Self serving for me, but if you're having trouble with the Polynomial algorithm, try the Linear algorithm: see Jasem's latest announcement about 3.4.0 knro.blogspot.com/2020/02/kstars-v340-is-released.html

Tolerance is the percentage of HFR worse than the estimated best focus HFR that the algorithm is willing to "settle for". Setting it too tight, and the algorithm may never find it because of noise in the measurements and backlash and so on. Also, I know my Moonlight has backlash, I'd be very surprised if yours didn't. It's just that the driver has no mechanism for repairing it. The Linear focus algorithm attempts to deal with it.

Someday we'll have a focus wizard to set all these parameters :/

Focus (and align) can fair for reasons that can't be fixed, e.g. a cloud comes by. I agree that the system should be able to recover from those. You bring up a valid point that the system should not try to re-align 196 times

I've thought that we should also have a maximum HFR parameter, e.g. the AF algorithm should fail if the best HFR was 5. Do you have a log for that 196x align run?

Hy

Thanks to everyone offering help.

Unfortunately I didn't save a log. But I did manage to cut and paste the windows from both focus and alignment to text files. It's obvious from the screen shot that the focus system got out of focus by looking at some noise and not an actual star. This was half way through the evening (I had been imaging about 6 hours with refocus set every 45 minutes due to temperature variation). There must be some kind of threshold that could be set so that the focus algorithm doesn't pick up on noise, and insures there's a star. The star, when there, is obvious visually as it's a point source multiple pixels wide. The noise is clearly not a white point source. And this camera the ASI2600 is extremely low noise. I have the low profile Edge Moonlite focuser using the Pegasus Astro UPBV2 focus controller which does have backlash compensation, but they recommended turning it off for the Moonlite.

Hy, I love your suggestion about a wizard that could create a "focus profile" for each scope. It could measure the average distance the focuser has to move, and can automatically set some parameters around that to keep from getting too far away from focus on accident. It would have to be linked to the scope, not the focuser as I use the same Moonlite driver for all my scopes.

Thanks for the input Hy, you probably understand the system way better than I do.

Updated to add scheduler log.

Andrew, one way of ensuring that actual stars are picked is by doing full frame focusing. And please try SEP as I suggested before because it is MUCH better at detecting stars.


Wouter

Yep, I will try that for sure. I was using full frame for some time as it did help with lots of focus failures. But switched back to single star as I thought it did a better job of getting better focus. Maybe it was all in my imagination.

As you had mentioned that before I think: That full frame usually gives slightly higher values for HFR is no issue. It is the relative variation that counts. Minimum is minimum...

And for SEP: If you're unsure what it is, this is the algorithm of sextractor in library form, which (AFAIK) is one of the most robust source detectors....

Does anyone know if it's possible to set focus to Bin 2x2 or 3x3 and achieve just as good of a focus? Full frame on the ZWO ASI2600 is 52.2 MB in size. It takes forever not doing sub frames.

Definitely fine to bin 2x2 for focus. In fact, if you zoom in on the picture where Jasem announced the new focus algorithm for 3.4.0 in knro.blogspot.com/ you can see I was binning at 2x2 on my Asi1600. Full frame focus is a good idea. Never tried 3x3.
Hy

PS Clear write up a review of your new camera--would love to hear more about it!