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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

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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
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The following user(s) said Thank You: R Dan Nafe
5 months 4 days ago #82655

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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.
5 months 3 days ago #82658

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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.
5 months 3 days ago #82662

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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
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5 months 3 days ago #82671

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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, RPi4b 8GB, Bullseye 64bit
5 months 1 day ago #82696

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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.
5 months 14 hours ago #82703

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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: 5 months 9 hours ago by Doug S.
5 months 10 hours ago #82710

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I don't know about this technical talk, but all I would love is to be able to use autofocus without having to go back in manually and move the focuser back out to the calculated spot - which is ALWAYS better than the final focus point that EKOS chooses. My whole routine has been to run autofocus, then manually move the focuser OUT about 800 points on the ZWO EAF (to prevent mirror tilt), and then back in to the previously calculated focus point. I image at 7,000 ft in central New Mexico, with humidity levels in the single digits. The difference between these two focus points is very noticeable and frustrating that EKOS aways chooses the worse point. At least it is consistent in that regard.

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
5 months 9 hours ago #82711

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Replied by Alfred on topic New Focus Algorithm in Ekos

Peter, why don't you make use of the "backlash" functionality in the focuser tab? Once activated, you only need to manually set the point of best focus and Ekos will take care of the rest, i.e. move the focuser further out and back in automatically.
4 months 4 weeks ago #82715

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Since f/ratio is known, "Critical focus zone in micron" could be calculated automatically (also with ccd-corrected formulae since we know sensor pixel size too). So only needed parameters are "Microns per motor step" and "Step size (CFZ units)". For "microns per motor step", I think the best approach for non technical users is to provide them with two fields: "maximum focuser travel (mm)" and "maximum steps (for total focuser trave)" and let the code do the division. This suggests the users to measure the max travel and not, to say, the needed steps to travel 1 cm, which is useful to reduce impact of inevitable measure error.

My 10 cents.
Matteo
4 months 4 weeks ago #82716

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Good point. So the focus routine can collect the needed data from the mount (f#) and camera (px size) sections.
254/1450 mm Newton, 130/730 mm APO, 70/336 mm APO, EQ6-R, ZWO EAF focusers, DeepSkyPro 2600c, ASI183MM, RPi4b 8GB, Bullseye 64bit
4 months 4 weeks ago #82719

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Alfred, I have done that, and it takes care of the focuser's backlash. But what I was talking about is the slight primary mirror tilt I get when the focuser moves it outward. I have found that my images suffer from very small tilt when the focuser ends it's movement outward. Fortunately EKOS ends it's movement INWARD, which is great, but it overshoots the ideal calculated spot forcing me to backup and move the focuser outward to the best focuser position. That adds the tilt. So I have to first go outward quite a ways, and then back inward to straighten the primary.

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
4 months 4 weeks ago #82724

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