×

INDI Library v1.9.8 Released (29 Sep 2022)

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

New Focus Algorithm in Ekos

  • Posts: 384
  • Thank you received: 115

Replied by Doug S on topic New Focus Algorithm in Ekos

Hi Ron,

A couple thoughts for you. I like the approach, it has a BIG advantage over the current linear alg in that it doesn't "pull up short" which has previously been described by prior posts on the subject.

My only suggestion is to consider whether you want to make the same mistake Linear Alg made in the Mechanics tab. Picking an "Initial Step", and "Out Step Multiple" has created a lot of unnecessary confusion for folks. In reality, the "proper" way to define the step size and out step multiple is to calculate those parameters from other system info as it relates to CFZ. Knowing the focus drawtube screw pitch and motor scale would ensure the correct step-size is used. Alternatively, not knowing these parameters creates the conditions for step-size exceeding the CFZ (jumps over), or too small (wasting focus time). This is completely avoidable. You might want to consider at least having an option to calculate the step size, correlating to CFZ, motor scale, and focuser thread pitch size. See the following info which might help:

www.goldastro.com/goldfocus/ncfz.php

Cheers, and good luck, Doug S
RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.
7 months 2 days ago #82642

Please Log in or Create an account to join the conversation.

  • Posts: 225
  • Thank you received: 15
Doug,

Thanks for the thoughts. I have read this article and find it interesting. I guess that I have used "trial and error" for my different scopes and focusers.

Like others, I find that the "one pass" does a pretty good job at finding the best focus. The second pass process, while theoretically valuable, does little to improve the focus. In fact, it usually was the cause of creating an error, aborting and restarting the process.

I'm looking forward to using John's new process!

Ron
Mounts: Sky-Watcher EQ6-R Pro, Meade LX85, Celestron NexStar Evolution Alt/Az
OTAs: Celestron 8" Edge HD w/Hyperstar, Meade 80mm APO Triplet Refractor
Cameras: ASI533MC Pro, ASI183MC Pro, ASI224MC, ASI120MC-S, ZWO ASI290MM
Raspberry Pi 4 with Stellarmate OS, MacBook Pro
7 months 2 days ago #82644

Please Log in or Create an account to join the conversation.

  • Posts: 184
  • Thank you received: 46

Replied by John on topic New Focus Algorithm in Ekos

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?
7 months 2 days ago #82645

Please Log in or Create an account to join the conversation.

  • Posts: 184
  • Thank you received: 46

Replied by John on topic New Focus Algorithm in Ekos

Thanks Doug, I'll take a look at this.
7 months 2 days ago #82646

Please Log in or Create an account to join the conversation.

  • Posts: 225
  • Thank you received: 15
John,

I only use the Celestron focuser with the linear method of my Celestron 8HD Edge. I'm not sure that I would describe it as an issue with the mechanics... the current process just doesn't give the focuser time to complete the "out" movement before it issues an "in" command. It may be working fine and I'm simply experiencing what Doug is describing. However, when I'm sitting at the scope it sounds like it starts reversing before it finishes the out movement.

This is one of those situations where I would think it wouldn't hurt to have a very short (1 sec) pause between commands.

BTW... I'm not fond of the Celestron focuser. I sometimes experience connection issues with INDI... seems unstable. I've ordered an ZWO EAF to replace it on the 8HD Edge, but have been waiting several weeks for the back order to clear.

The ZWO EAF on my refractor works perfectly with the polynomial process.

Thanks for your effort!

Ron
Mounts: Sky-Watcher EQ6-R Pro, Meade LX85, Celestron NexStar Evolution Alt/Az
OTAs: Celestron 8" Edge HD w/Hyperstar, Meade 80mm APO Triplet Refractor
Cameras: ASI533MC Pro, ASI183MC Pro, ASI224MC, ASI120MC-S, ZWO ASI290MM
Raspberry Pi 4 with Stellarmate OS, MacBook Pro
7 months 2 days ago #82647

Please Log in or Create an account to join the conversation.

  • Posts: 522
  • Thank you received: 103

Replied by Jim on topic New Focus Algorithm in Ekos

Would it be possible to have the system determine what the step size should be in some way each session? The starting step for determining the final step size could even be calculated from the user's equipment configuration. Store this value and use it as the seed for the next time an auto-configure of step size is run.
12" pier with HDX110 using EQMod
ASI 1600 mono/color mains with ASI290MM in off-axis
ASI filter wheel
Moonlite focusers for the sharpening
AT115EDT w/.8x for the light
Fedora Linux, 100% INDI
The following user(s) said Thank You: R Dan Nafe
7 months 1 day ago #82655

Please Log in or Create an account to join the conversation.

  • Posts: 184
  • Thank you received: 46

Replied by John on topic New Focus Algorithm in Ekos

Thanks for the reply Jim, let me know if you have any suggestions on what the step size algorithm should be.
7 months 1 day ago #82658

Please Log in or Create an account to join the conversation.

  • Posts: 384
  • Thank you received: 115

Replied by Doug S on topic New Focus Algorithm in Ekos

Hi John, IMHO, the only step size that is "appropriate" is one that is tightly correlated to the CFZ size (in microns) for the instrument. This is what the Critical CFZ discussion I previously posted is all about. It's seeing and focus tolerance dependent after factoring f/ratio and aperture size. Whether one wants to be conservative and use a step size that is 1/2 CFZ (to always be sure to land in it), or less conservative (~1 CFZ) could be a user choice (but with potential consequences).

It would be best if the algorithm calculated step size from user input of how many microns per revolution the focus motor has, and how many microns of focuser drawtube travel occurs per revolution of the focusing mechanism. Not knowing these two values, and just "winging" a generic step size is just guessing. Folks should try to get some understanding of their CFZ and then set a step size to match the instrument. Since some will not want or know this info (or won't want to go to the trouble to find it), the guess may need to be allowed. But a better solution would be to allow for a precise calculation when the parameters are known.
RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.
7 months 13 hours ago #82662

Please Log in or Create an account to join the conversation.

  • Posts: 827
  • Thank you received: 96
Thank you, thank you, thank you!!! Several of us have been saying for almost two years about the linear auto focus always choosing the wrong focus point. I always had to go back in and move it back to the pre-calculated (from the first pass) position which was ALWAYS better than the spot EKOS stopped at. I baffled me why it go through the trouble to calculated a perfect focus spit, then choose a spit just inside of it. I image with a C11 w/ the ZWO EAF and the initial calculated point always produced a better focus point.

What I found worked was to let EKOS run through the first pass, and then I would move the focuser outward a ways (to take up the backlash) and then move it inward to the calculated spot. It worked great - but was basically manual.

With the C11 EdgeHD and ZWO EAF it was important that the final focus movement was INWARD. Otherwise I would end up with some mirror tilt.

iOptron CEM120 EC2 and CEM25P
Celestron C11 EdgeHD and William Optics Star71
ASI 1600MM Pro, ASI 462MC
Moonlight Litecrawler (C11) and Motorfocus (WOStar71)
LodeStar X2 and ZWO OAG
Nextdome, AAG Cloudwatcher
MacMini
The following user(s) said Thank You: R Dan Nafe
7 months 5 hours ago #82671

Please Log in or Create an account to join the conversation.

  • Posts: 134
  • Thank you received: 13
Concerning the CFZ discussion, to determine the microns per motor step one could simply measure the max. drawtube travel and the corresponding step delta and divide those figures. So no need to know the drawtube screw pitch and motor scale.

The linear 1-pass algo (in principle any focus algo) then could have 3 additional (optional) input fields: "Microns per motor step", "Critical focus zone in micron" and "Desired step size in CFZ units". The latter can default to 0.5, but the user can overwrite it (using 1, for instance, or whatever).

The calculated step size would then be "Desired step size in CFZ units" x "CFZ in micron" / "Microns per motor step". Alternatively, the user can ignore those additional input fields and enter the step size manually as it is today.
254/1450 mm Newton, 130/730 mm APO, 70/336 mm APO, EQ6-R, ZWO EAF focusers, DeepSkyPro 2600c, ASI183MM, Intel NUC 8i5, Ubuntu 22.04
6 months 4 weeks ago #82696

Please Log in or Create an account to join the conversation.

  • Posts: 184
  • Thank you received: 46

Replied by John on topic New Focus Algorithm in Ekos

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.
6 months 3 weeks ago #82703

Please Log in or Create an account to join the conversation.

  • Posts: 384
  • Thank you received: 115

Replied by Doug S on topic New Focus Algorithm in Ekos

Hi John, non-professional sites typically have seeing in the 2.5 to 3.0 (or worse) category. Folks love to claim they have sub 1 arcsecond seeing in their backyards, but well....you know how that goes. Anyway, I'd suggest defaulting to 3 and then users could change it if they want. You could also default tolerance to 10% (which should be fine).

Remember that only very fast telescopes (f/2 - f/5) will be particularly sensitive to the values. Those with f/7 to f/10 systems have such large CFZs that it's not going to matter much. About the thread pitch and motor spec, I was being technically precise, but not implying that folks need to locate that info. The vast majority of people will simply run some reasonably large number of motor counts and measure the millimeters of focuser travel. If you allow entry of those numbers in the GUI (measured mm travel and motor steps for that travel) the alg could solve for microns/step internally to avoid that confusion for users. Cheers Doug
RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.
Last edit: 6 months 3 weeks ago by Doug S.
6 months 3 weeks ago #82710

Please Log in or Create an account to join the conversation.

Time to create page: 0.377 seconds