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Bi-monthly release with minor bug fixes and improvements

Focus is not good

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Replied by John on topic Focus is not good

Hi Morelli,

Thanks for posting the screenshots. I'll concentrate on the Linear 1 Pass focus runs. From your signature it looks like you're using a MAK180 SW and ASI183MM PRO. I don't know if you have a reducer, if not you're at FL 2700 f/15. The pixel size is 2.4 microns which gives an image scale of 0.18"/pixel for bin 1. I see you're 2x2 binning which would be 0.36"/pixel.

Are you running Autofocus with the Bahtinov mask on? Or adding it after Autofocus completes in order to compare the focus position with the Bahtinov? I'll assume the latter. Out of interest what is the focus position that the Bahtinov gives you?

You imply you are using a single star to focus rather than using multiple stars. Is that correct? Either should be OK but I always use multiple stars (but am at a much shorter FL). If you do use multiple stars then its worth checking the "Use weights" option.

The curves in general look ok in terms of number of points and total HFR change from min to max. I suspect, however, that with the Mak you will be suffering from donuts when you move out of focus. I can't tell from the screenshots though.

Given your FL, the exposure times seem short (1 and 3 seconds). You are averaging over 3 or 5 frames. Personally I would increase the exposure time maybe to 4 to 5 secs and average over 1 frame. If you have a lot of saturated stars at 5 secs you'll have to reduce the exposure time.

When you are on the first and last datapoint (out of focus) how is the star detection? You can move to that focuser position and take a frame. If you zoom in you can see how well (or not) star detection is working. I see you are using the "SmallStars" SEP profile. Is there a reason for that? Have you tried the "Focus" SEP profile?

One other thing we could try is if you set the "Save Focus Images" option. The focus images are saved in the same directory as log files. You could turn this option on, do a focus run, then send me the images. You probably will want to then turn the option off so you don't fill up your disk. I'm happy to play around with star detection with these. This is how to turn the option on..
.

One more thing... backlash. The v-curves don't show any evidence of backlash which is a good thing. But how are you controlling it? What settings do you have? When Linear 1 Pass goes to the solution the algorithm has calculated, its imperative that the focuser is able to perform that final outward motion with well controlled backlash. So there are a couple of ways to do that:
1. Does the MyFocuserPro do its own backlash control? Is this what you are using? If so, does it manage mirror flop (if you have any on the Mak)?
2. If the MyFocuserPro is not controlling backlash how are you controlling it in Ekos? Is the driver controlling backlash? If so, are you sure this is working correctly?
3. AF Overscan should work with the Mak to overcome any flop. Are you using it?

Sorry for all the questions, but hopefully through the dialog we'll get a good solution.
11 months 2 weeks ago #91794
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Replied by John on topic Focus is not good

One way to see if backlash is well controlled is:
1. Put the Bahtinov mask on and get to focus. Say its 6321.
2. Take the mask off and take an exposure. Note the HFR. Repeat 5 times.
3. Move the focuser to approximately the most inward point on an autofocus run, say 6000.
4. Move the focuser back to 6321.
5. Take an exposure and note the HFR. Repeat 5 times.
6. Put the Bahtinov on and see if you're in focus.

If the HFRs before and after match and the Bahtinov tells you that you in focus (in point 6) then all is well. If not, then there's a problem with the focuser / backlash compensation.
11 months 2 weeks ago #91797

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Replied by MORELLI on topic Focus is not good

Hi John,

My setup for the tries is with the ED80 + reducer 0.85 (FL 510, F/D 6.3 - FL 522 F/D 6.5 mesured).
I used the Bahtinov mask for comparison. The first position for the Bahtinov was 6405. But this position changed after but I didn't note it.
I used multi-stars after aiming at a star: Capella next Castor.
The motor of the focuser has not backlash.
The SmallStars option matches with my FOV I think.
This evening I 'll save the focus image in order to send it you.

On the beginning, I measured the HFR of a single star in order to determine the initial step. I setup it to 10 for my measures. The results are strange:
Position HFR
6405 1.39 (Bahtinov position)
6415 1.29
6425 1.30
6435 1.27
6445 1.43
6455 1.46
6465 1.98
6475 2.79
6485 2.49 - 2.69 - 2.41 (one frame) 2.19 - 2.56 - 2.64 - 2.53 (5 frames)
6495 2.97 (5 frames)
5005 2.19 (5 frames)
5015 2.41 (5 frames)

I control the focuser this morning. There is a problem. The lenght max is 80mm from 0 (external) to 10000 (fully retracted). One tour=18mm
I measured the lenght for position 6500 starting from 10000. Successively, 24.6mm, 27.6mm, 27.6mm, 29.3mm.
I tightened the nuts of the focuseur. 27.7mm and starting from the external position (0) 29.5mm.
11 months 2 weeks ago #91799

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Replied by John on topic Focus is not good

Hi Morelli,

Thanks for the info. It should be much easier with the ED80 at f6.5! I think 1 to 3 secs exposures will be fine so ignore my suggestion to increase this. Also ignore my comments on donuts. The image scale is 0.95"/pixel so either bin 1or bin 2 (as you have)

As you mention sounds like something is slipping. That 6 point test I mentioned this morning will be a good test. It should be possible to get the focuser in focus then move away and back to the same spot and still be in focus. This is what Linear 1 Pass (as well as Iterative and Polynomial) rely on.

When you mention "The motor of the focuser has not backlash." whilst this may well be true, there could be backlash in the drawtube mechanism and/or the focuser binding to the drawtube.
11 months 2 weeks ago #91804

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Replied by MORELLI on topic Focus is not good

Hi,

I do my tries on saturday night (not fever). Conclusion, I have to change my focuser. I can't be confident with it, poor quality perhaps. I look for a Kepler M-LRA that fit on my ED80. Do you think it is a good choice ?
11 months 2 weeks ago #91858

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Replied by a Guest on topic Focus is not good

A conceivable explanation for this could be a problem with your hardware such as your focuser or camera. There may also be an issue pertaining to the software that you are using like Stellarmate or Astroberry.

To troubleshoot this, try adjusting settings on your equipment say, the focus motor DIY or trying out different autofocus algorithms to check if they generate better outcomes. You can also regulate your camera's settings such as exposure time or ISO levels to observe whether this makes any improvement in the quality of captures.

Manual focusing could be another choice albeit it is time-consuming but it may yield better results sometimes. You can also opt for a Bahtinov mask and other focusing aids that may facilitate achieving more precise focus.

If autofocus still turns up errors, contacting the maker of your hardware or software for extra support might serve a good purpose.
11 months 2 weeks ago #91860

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Replied by John on topic Focus is not good

Hi Morelli,

I have a ZWO EAF which works well on my SW 100ED. I don't have any experience with the focuser you suggest - maybe others can comment? Obviously it will need an indi driver to be useable from Ekos.

On the myFocusPro, I know some other folks on here have the same focuser. Maybe you could create a new post and see if other folks can help with the problem you have.
11 months 2 weeks ago #91861

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Replied by MORELLI on topic Focus is not good

When I talk about focuser, I mean the mecanical part of the ED80. So I would replace this Crayford model with the Kepler M-LRA.
My Robert Brownb model focuser with MyFocuserPro2 driver works perfectely.
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Last edit: 11 months 2 weeks ago by MORELLI.
11 months 2 weeks ago #91872

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Replied by MORELLI on topic Focus is not good

I made a complete setting of my Crayford. I made tests this afternoon with the conceptor of the focuser.
First just placed on the table, then vertically, the weight being maximum.
All seem to run perfectely.
A noted position, 3500, was retreived at every move.
Just to wait for a cleary night now and real tests.
11 months 2 weeks ago #92010

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