Hi Doug, Matteo, Jim and Bernd,
I reached out to Jeff Winter at GoldAstro to see if he would be willing to collaborate. He's currently busy on a project but said he'd get back to me, so I'll let you know how things go. I'm sure you've seen the calculator on the GoldAstro website:
So as we started off discussing, as a way to ensure Step Size is set to a "sensible" value this could have some merit. Don't forget though that we should be able to do better than just "somewhere in the NCFZ" by curve fitting the datapoints.
So for the inexperienced user it should provide some assistance during setup but I'm not sure it provides anything to the experienced user who has spent time working out his/her setup and has arrived at values that suit their equipment. Or am I missing something? What would your workflow be if this feature was available?
Hi Ron, I debugged my ASI EAF through the hokey-cokey to see how it coped with the outward then immediately afterward, inward movement. The code is event driven with a user defined "polling" period (say 500ms). So an outward motion is started and every 500ms the focuser is queried to see what's happening. If the focuser is still moving then the system waits; if the focuser has completed the motion then the system starts the inward motion.
I don't have a Celestron focuser so I can't do the same thing with that. The only things I can suggest are:
1. Make sure you're on the latest version of Indi and the drivers to ensure you have the latest bug fixes.
2. If the Celestron driver works like the ZWO EAF, then there will be a polling period in the Indi tab that you can set. You could try upping the value and see if that fixes your problem.
3. If the above don't work you could raise an issue and hopefully someone with knowledge of the Celestron driver would be able to take a look.
Hi Doug and Bernd,
I started looking at the CFZ. Some observations:
1. Whilst I easily found the steps / revolution of my focuser, I can’t find the thread pitch of my SW draw tube. I think it has a 1:11 gearing but that may be incorrect so I’ll have to measure movement per focuser step as Bernd suggests. Since I don’t have anything other than a ruler to measure this the result won’t be very accurate, but I’ll give it a go.
2. Bernd suggests 3 parameters to capture which is of course possible.
3. In addition some decisions would need to be made on:
a) Seeing. Would need to capture a value from the user for astronomical seeing or total seeing. Could calculate the diffraction component for the telescope based on filter (wavelength of light being used) but this may be overkill.
b) Tolerance %. The article quotes many different values from a few % to a few 10%. Based on the formula this has a sqrt(tolerance) impact on NCFZ.
I have to say that this looks like it will require quite a bit of knowledge from the user to fill in the correct data to get a reasonable answer for NCFZ and then step size. For those that know this info the GoldFocus website provides a calculator to do this so I’m not convinced putting it in EKOS would provide much benefit.
Just my initial thoughts.
Thanks for the reply Jim, let me know if you have any suggestions on what the step size algorithm should be.
Thanks Doug, I'll take a look at this.
Thanks Ron, I'll take a look. I see you have a Celestron Focus Motor and ZWO EAF. Do you think both have this issue?
Thanks for replying. On the standard deviation:
1. If single star mode is selected, the SD option is disabled.
2. For multi-star... the stars go through an extraction process to find suitable candidates (I haven't changed this). There are several options but if you use the default SEP there are many parameters to control this, for example removing clipped stars and those below a certain brightness. After this process has run there will be a set of stars that meet the criteria and each has its HFR calculated. I then calculate the SD of this set.
The star set will vary from frame to frame and there is some existing work in Linear to try and use the common subset of stars for consistency. I am trying to use this in Linear 1 Pass, but there is still some work to do. Variation in brightness of the stars should not affect the HFRs too much (assuming the extraction and processing parameters are set reasonably).
The variation in HFRs will depend on focus effects, seeing, etc. but I think its a reasonable measure of "quality" for the focus point. What I've observed on my equipment is a trend whereby SD increases with distance from optimum focus but then certain points deviate from this with transient effects like seeing, wind gusts, etc etc.
As to whether applying weighting makes enough of a difference to the calculated optimum focus point to be noticeable, I don't know. We'll just have to give it a try.
Thanks for the reply. So what happens with Linear is that whenever it moves outward it does the "backlash hokey-cokey" by moving "2 * Step Size" further outward than needed, then when that completes, it moves inward by "2 * Step Size". Step Size does get changed by the algorithm but it will never be bigger than the Initial Step Size field on screen. So, for example, if Initial Step Size = 40, then it will correct for 80 ticks of backlash... if you have, say 100 ticks of backlash, then 20 will be uncorrected.
With Linear 1 Pass there will be 2 ways to deal with backlash:
1. Same as Linear (if on-screen backlash field is set to zero).
2. User entered backlash into on-screen backlash field. The hokey-cokey will be use this value. So in the above example, if your real backlash is, say 100, then set the field to 200 and you'll be fine.
Hopefully this would fix your issue.
I'm in the process of writing a new focus algorithm for Ekos. If your focus already works well then there's probably not much here for you so you might want to just keep on scrolling!
For my equipment, the Iterative and Polynomial algos don't work very well because of the backlash in my ASI EAF. Linear works the best but usually finishes up overshooting the point of optimum focus. So I'm building a new algorithm, called "Linear 1 Pass" that is based on Linear but does a single pass, works out the point of optimum focus in that pass, and moves to that point.
Here is a write up of what it does...