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INDI Library v1.9.9 Released (30 Nov 2022)

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

For those with focus issues

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I am troubled cause this is how it goes:

1. Manually I go as far as good I can, regularly HFR 1,2-1,4 and then start Auto Focus.
2. Iterration 1: 40+ stars found across the circle 
3. Iterration 2: 20 stars found only on one side of the circle
4. Iterration 3: 5 stars found, 3 on the right, 1 on the top and 1 at the bottom 
etc..
(Tried multiple steps from 100 till 10.)

I can see that on the the 1st pass went down for example to HFR 1.2, but then - cause it looses all those stars - the calculation changes and increases. 
​​​​​​
So when it finally says done after 20 Iterrations, there are only 5-6 stars with HFR 2+
11 months 3 weeks ago #80372

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Last night...

After meridian flip, tried 3 times the autofocus (while I was quite close to focus) and every time I could a different step number. So I left it unattended without any change, to refocus every 60'.

While reviewing now the images:

Hour 1 (when I pressed autofocus) :

 

Later on:

 


This is driving me crazy....Clear skies, perfect conditions.
 
11 months 3 weeks ago #80436
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Update: As it seems the "Out Step Multiple" has a great impact - at least for my setup and workflow. I remember that I've lowered it to 2, hoping for quicker result.
As soon as I got it back to 5, everything works just fine 
11 months 2 weeks ago #80669

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Replied by Martha on topic For those with focus issues

Hi guys,

I'd like to refresh the thread. Recently I bought a better class Altair triplet and the first impression says that it has a higher quality focuser. I tried to compare the refractor with another one that I have, it's optically superb Altair Starwave 102ED F/11 equipped with an ATM motorised focuser controlled manually via Arduino. I tried to capture Mars using the two refractors subsequently. I found that the focuser of the triplet keeps the planet perfectly in one place (excellent PA), while the focuser in the cheaper F/11 doublet is lifting the planet up or dropping down depending on moving the rocuser inwards or outwards. Did you take this problem of cheaper focusers into account?

Very soon after purchasing the triplet I decided to buy the ZWO EAF. I already performed three motorised focusers, one is driven straight by OnStep/Ekos, while two other are driven by the Arduino and my code. In the case of the triplet I expect excellent quality and comfort of focusing, that's why I ordered the EAF. It's installed now and waits for the clear sky. I'm going to perform a test of the backlash by moving it outwards for a number of steps and inwards.

My EAF is attached straight to the main axis of the focuser instead of the single knob and here I have a question about the number of initial steps. Some of you write that they set initial steps of 200-500 ticks, while others write that they use 20-50 ticks. What does it depend on? I have read all the thread and nowhere is mentioned whether the stepper motor should be attached to the main axis or to the 10:1 reducer axis. The ratio of 200-500:20-50 suggests that the bigger values are related to the reducer axis. I found (using a Bahtinov mask) that I get focus around 7600 ticks, which is around 27mm from its absolute zero position. Is it OK?

My second question is about the bin2 mode. I use a Canon 6D that has a quite big 6.54um pixel. The cameras mentioned within the thread usually have something about 3.7um pixels. I understand that my pixel works like 4 others, so should I consider the bin2 mode (if the Canon 6D offers it)?

I use a 3" x1.0 field flattener, so my stars are slightly elongated on edges of the full frame and of course in the corners. I think the 75-80% as the second value of the annulus should be OK.

I consider configuration like below:
- full field (should the "autoselect star" be selected then?),
- annulus 25% - 75(80)%
- SEP,
- linear algorithm,
- 5% tolerance,
- initial step 50.

Please let me know if I should think about something else. The good weather in the UK is so rare that I have no time for long experimentation. I appreciate your common experience and knowledge.

I will test with pleasure whether the linear algorithm brings the same focus point and the HFR like the polynomial one. I have experience with 10" budget Newtonian OTA equipped with Hexafoc 2.5" RnP focuser and the polynomial algorithm working with the ATM geared stepper motor (OnStep) and I was quite happy with the results, if the process was successful. Unfortunately, most often it fails. I hope the linear algorithm with the EAF attached to the high class focuser will surprise me positively.

Best regards,
Martha
* Altair 102EDT F/7 @ Opus Magnum ATM EQ Fork Mount / OnStep / Astroberry
* Altair 102ED F/11 & Vixen A80M + bino @ EQ5

www.astrobin.com/users/Vroobel/
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1 month 4 days ago #89270

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"I'm going to perform a test of the backlash by moving it outwards for a number of steps and inwards."

Do you mean "backlash", "slippage" or "missing steps"? Slippage and missed steps is going to be the much bigger problem than backlash. With a heavy camera, both can become a massive problem, especially if your telescope is nearly vertical.


"My EAF is attached straight to the main axis of the focuser instead of the single knob and here I have a question about the number of initial steps. Some of you write that they set initial steps of 200-500 ticks, while others write that they use 20-50 ticks. What does it depend on? I have read all the thread and nowhere is mentioned whether the stepper motor should be attached to the main axis or to the 10:1 reducer axis. The ratio of 200-500:20-50 suggests that the bigger values are related to the reducer axis."


Depends on 1) your code (how many steps does it allow), 2) on the torque your stepper motor can deliver (if attached to the main axis, you will probably require microsteps to achieve precise focus resolution. Microstepping reduces the available torque and will likely result in missed steps, especially when the telescope is nearly vertical and has to lift the camera and everything attached to it, so I have my focuser (also controlled by Arduino) attached to the reducer axis to minimize the need for microstepping.
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Last edit: 1 month 4 days ago by Jose Corazon.
1 month 4 days ago #89271

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Replied by Doug S on topic For those with focus issues

Hi Martha, you might want to read my comments (multiple) on page 3 of this post:

indilib.org/forum/ekos/11668-new-focus-a....html?start=24#82726

Basically, you shouldn't need to guess the step size. It should ideally be calculated from your CFZ size, EAF/focuser drawtube travel, and a couple of user selectable parameters. See the formula for New CFZ as defined in the post above. Then you'll want to know (or measure) your focuser travel per revolution and match this up to the EAF counts/rev. Set your step size to be somewhere between 1/2 and 1 CFZ. You don't want to jump over the CFZ, and if you set it too small, you'll just waste time during focus jumping within the same CFZ. As for how the EAF is mounted, If I remember correctly from the user manual, you should not mount on the 10:1. The counts/revs is already plenty high enough to do fine focus work as is. Expect backlash on the order of 85 counts (That's about where mine was when I tested, and it was confirmed by others in the forum with EAF).... Good luck & CS, Doug S
RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.
The following user(s) said Thank You: R Dan Nafe
Last edit: 1 month 4 days ago by Doug S.
1 month 4 days ago #89272

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Replied by John on topic For those with focus issues

Hi Martha,

If you haven't already, I'd suggest you have a look at the focus section of the kstars manual...
docs.kde.org/trunk5/en/kstars/kstars/tool-ekos.html#ekos-focus

It discusses the various algorithms and by all means give them all a go, but I'd suggest Linear 1 Pass (although since I wrote it I'm obviously biased!)

There is a section on "How to Setup for an Autofocus Run" which goes through some good starting values for various parameters and the trade-offs to consider. If you find anything unclear, wrong or missing let me know and I'll update the document.

Good luck and let us know how you get on.

John.
1 month 4 days ago #89274

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Replied by Martha on topic For those with focus issues

@Jose, @Doug and @John,

Thank you for your answers. in the beginning I decided to fillow the Doug's advice, especially that I understand all the NCFZ rule.

1. I measured the full travel of the focuser tube using a caliper and it's 94.4 mm. In the meantime the EAF performed 25,992 steps.
2. I found out that 1 step/tick mens 3.631886734 µm, please correct me if I'm wrong.
3. I didn't find whether for the diffraction limit I should use the Dawes limit (120/D) or the Rayleigh limit (140/D) so I took an average value 130/D.
4. I solved the equation for the 102mm F/ refractor and for everage seeing that is usually around 2 arcsec and my NCFZ is 42 µm.
5. I found on the 2nd page of the mentionet thread that the Step Size should be equal to 1/2 of the NCFZ. Should I understand that if 1 µm means 0.275338983 of the step/tick then the 1/2 of the NCFZ is 21 * 0.275338983 = 5.783512841
-> 6 steps ???

Edit.
Sorry, my fault, I have F/7 OTA now, not F/5. That means the NCFZ = 82.33984917, half of it is 41.16992458 and the Step Size is 11.33568517 -> 11
/Edit.

I cannot believe that so small movement may change something.

I really want to understand it, so Doug, please help me.

Martha
* Altair 102EDT F/7 @ Opus Magnum ATM EQ Fork Mount / OnStep / Astroberry
* Altair 102ED F/11 & Vixen A80M + bino @ EQ5

www.astrobin.com/users/Vroobel/
Last edit: 1 month 3 days ago by Martha.
1 month 3 days ago #89281

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Replied by Martha on topic For those with focus issues

I made a quick test. I assumed that the Step Size comes from not 1/2 NCFZ, but straight from the full value of the NCFZ, so the Step Size is 26. If the linear algorithm moves the tube owtwards for 10 x Steps Size that is 260 steps, then the tube moves outwards less than 1mm. And that should be OK, as my calculation says that 1mm means 275.3390 steps.

But my question is still going: if the proper sampling begins after coming back, inwards, at the position of -5 steps, so is it able to find the focus within less than 1mm? (-5 steps, +5 steps)?

Martha.
* Altair 102EDT F/7 @ Opus Magnum ATM EQ Fork Mount / OnStep / Astroberry
* Altair 102ED F/11 & Vixen A80M + bino @ EQ5

www.astrobin.com/users/Vroobel/
1 month 3 days ago #89282

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Replied by Doug S on topic For those with focus issues

Hi Martha, Point #2 as calculated is technically correct... however, I don't believe it (from a sanity check perspective).

From my calcs, your CFZ is 71.1 um @ 10% focus tolerance, and 87.1 um @ 15% tolerance. This seems right to me for f/7. If you're getting 2 arcsec seeing, I'd constrain to 10% tolerance or better...you don't want to waste good seeing with poor focus!

Now, about that travel measurement.... I'm having a hard time believing the measurement (unless I didn't understand what you said). I would have expected you to have at least 3-4 hundred motor counts for a CFZ that size, but you've measured 94400 um / 25992 motor counts or 3.632 um/motor count (only 0.27 motor counts/um). Are you sure you did that measurement right? You might want to measure again (or tell me what I didn't understand). In the end, I'd expect to find for f/7 something on the order of 300-400 motor counts per CFZ, and a corresponding step size of 250 or so (educated guess). How about a 2nd measurement of your focuser travel and EAF motor counts. Make sure you push one direction with the EAF for at least 100 counts (to negate backlash), and then start your test in the same direction, noting your starting EAF motor count, travel distance, and final motor count. I'd be curious to hear the result. Cheers, Doug
RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.
1 month 3 days ago #89284

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I think that value isn't unreasonable for an EAF directly connected to the focuser shaft. Mine (Sharpstar AL-140PH) has 2.8μ steps (coming from my BL measurements, using a micrometer gauge). And yes, 20 steps give a clear difference in HFR (I do have quite good seeing).
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1 month 3 days ago #89286

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Replied by Doug S on topic For those with focus issues

Hi Peter...ok, that means that the focuser has a pretty coarse thread pitch. I'm not used to that. Celestron has a typical thread pitch of 0.75um/rev, leading to a 0.13um/EAF step, so I get many more steps in my CFZ. Just wondering out loud, I wonder at the measured low counts/CFZ, maybe the 10:1 gear would have been an interesting test to get more sensitivity? I'm not recommending anything other than what EAF recommends, but it does make me wonder. Martha can measure and confirm (or not) if she has about what you have. As long as it works... Cheers, Doug
RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.
1 month 3 days ago #89287

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