Peter Sütterlin replied to the topic 'Problem to connect ASi EAF' in the forum. yesterday

Not sure if that is an issue here. But in my experience the ZWO drivers have problems when a connected device disappears. In my case it was a bad power connection. After such an event, you have to restart the driver (indi_asi_focuser) before it will recognize the EAF again.

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I'm using eqmod cable and driver for my GP-DX, which has one of the EQ3/5 upgrade kits installed. Initially, before getting the eqmod cable, I had used the HC to connect, and ISTR that the HC has to be put into a special mode so it listens on the input port and translates it into proper commands for the motor controller. Did you do that?
Depending on what cable you ordered, if it is an eqmod cable (which includes AFAIK an USB-to-RS422 converter) it would have to be plugged to the motor control box instead of the HC.

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Peter Sütterlin replied to the topic 'For those with focus issues' in the forum. 3 weeks ago

@Martha: What version of kstars do you run? L1P was added in July (git), and was in the 3.6.0 release, so I had just assumed most people run it by now. My fault :o . No worries, just keep in mind to test it once you update to something >= 3.6.0 :D

As for measuring backlash:
Make sure the BL compensation in the driver is off.
Do two focus runs (with linear), note the average value. Then go to the INDI tab of the EAF. There's a 'Reverse Motion' Button. Toggle that, and repeat the focus runs, twice again. The difference of the two values should be a quite good starting point for the BL compensation.
If clear sky is too expensive to waste you can also do it inside, but you need a good caliper. Just step the EAF in one direction in small steps, and with each step measure the position of the focus tube relative to the OTA. Once the change is linear, step in the other direction, again noting the focuser tube position. Continue until that one changes linearly.
If you plot those (position vs. EAF reading) you should see two straight lines, maybe some deviations in the start and turn area. Draw a horizontal line through a region where both are linear, and look up the EAF readings for the two positions were the horizontal line crosses the two sloped ones. The difference is your BL.

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Peter Sütterlin replied to the topic 'For those with focus issues' in the forum. 3 weeks ago

I'd like to share results of my first focusing with the EAF and the linear algorithm: I love it! :woohoo:

Hehe, who would have thought that :cheer:

If you have time, definitely also gibe Linear 1Pass a try, using the 'Parabolic' or 'Hyperbolic' methods, including weighting. For me, that is even more stable than simple linear.

For the comparison with polynomial: Keep in mind that that one doesn't do any backlash compensation, and does move in both directions. So to do it justice, you'll first have to measure BL, and activate BL compensation in the driver - else the results will be very random... :(

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Peter Sütterlin replied to the topic 'For those with focus issues' in the forum. 4 weeks ago

Hi Martha,

yes, the long available range is to allow various optical configurations. Like adding a star diagonal for visual, various correctors, barlows or reducers etc. that require changes in back focus. If you only use one configuration it will stay at one position almost all of the time.

As for filter offsets, if (once...) you use a filter wheel there is the option to have a list of relative focus positions for each filter. You have some sort of reference (like L, or in case of RGB, G), and for other filters that table tells how much the focus differs from that value. If you then change to another filter EKOS will compute the needed focus change, and apply the difference, so that a consecutive AF run will already start at focus. Or you trust that, and start imaging. (I'm wary, and always do AF on filter change).

With manual filter changes that won't work, so forget about it for now.

And careful with the OIII filter - they are not really suited for color cameras, as many pixels will not get any light at all. There are special dual-band or triple-band filters made for color cameras. I have no experience with them, though. But my guess would be for a normal (photo) camera they might also be sub-optimal, as those cameras often block the light of Hα. So better ask around before taking (a lot of) money in your hands... ;)

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Peter Sütterlin replied to the topic 'For those with focus issues' in the forum. 4 weeks ago


I run my refractor (140mm, F/6.5) with a step size of 20, and the Linear 1P algorithm. The NCFZ for my setup/site is 31μ, or 11 steps. The chose step size stems from the first linear implementation that did the second run at half step size. I didn't change that when switching to L1P, but at least for me the interpolation it does usually leads to very good results.

As you mention, it is somewhat crucial to have a good start point, even without the donut problem (refractors don't have that). I think the (L1P) algorithm has improved in that respect, still it is (IMO) highly recommended to do an initial manual focus (I use a bright star and video mode). Doesn't have to be extremely accurate. And for automated AF, definitely use filter offsets if you use a filter wheel.

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Peter Sütterlin replied to the topic 'For those with focus issues' in the forum. 4 weeks ago

Hej Doug,

I'd say that isn't uncommon for standard rack&pinion focusers. And there's no real issue with that, IMO. That is why we use a stepper motor that has no problem doing single step accuracy. The 10:1 is for "clumsy fingers", but always has the chance of inherent slip, so it's really not recommended if you want reproducible focus-by-number. There's no gain of accuracy in having 'big numbers' when using a stepper motor.

As for the low 0.75μ/rev, that sounds to me like it is the movement of the main mirror, not the movement of the focus position, so that would get a magnification of about 10 from the secondary re-imaging, depending on your type of optics. Would still lead to quite large numbers, but that is really just focuser specific. A Crayford likely also has smaller step sizes than a R&P.

Cheers & Happy New Year!

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Peter Sütterlin replied to the topic 'For those with focus issues' in the forum. 4 weeks ago

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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The 'big red button' icon activates that stars/pixels above 60000 (IIR the value correct) are plotted red (also the total number of those is then printed in the status line). Would that suffice?

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Peter Sütterlin replied to the topic 'Mosaics using scheduler' in the forum. 1 month ago

Are people here now also starting to post ChatGPT answers without having a clue what they write about?

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Peter Sütterlin replied to the topic 'Solver is not working' in the forum. 2 months ago

Interesting. Or puzzling.
My only suspicion could be that indeed the pointing model (either of EKOS, or of the mount, if it has one) are somehow messed up. Like what I said about syncing close to the poles, if the coordinates that the mount slews to are badly off, the hinting ("Position") of course will not work if you are more than 30 degrees off. So that might explain why it falls back to blind solving.

The mount tab of EKOS has some button to discard mount models. I don't know if that also affects settings of the Gemini. Have you tried that? Else check the manual of the mount if there is a way (via HC?) to discard any stored models, and see if that helps.

Other than that, my pool of ideas is depleted... :(

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