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blinky

Cant get SGPro focus to work

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I have been trying for a few weeks now but cant get the autofocus to work properly o SGPro.  Initially I had the first move of the focuser a little flat and was told this was due to backash.  I have now increased it to 250 and last night the VCurves looked bang on, I also never got the error I had had previously where SGPro said the HFR was not as good as expected.   On looking today at an image though Im still not sure its in focus.  Im pretty much out of ideas of what else to change, especially as Im getting a good VCurve.

My setup is a Pegasus focuser, connected to a WO ZS73 which has a R&P focuser.  Hanging off the focuser is a OAG, ZWO Filter wheel and ASI1600.

image.thumb.png.db25dfc1fe1f632b9742408796763aec.png

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Difficult to say without seeing what is happening live...

I don't know the SGP focuser routine and only have experience with Focusmax but I have learned that it's important to select a non-saturated star and not to select one from the middle or edge of the frame but to choose one roughly at the one third position to give the best average focus value for the frame as a whole, even with a flattener there can be considerable focus difference between the middle and edge of the frame so the Focusmax recommendation is to choose a star close to the one third position (one third in from right/left edge, one third in from top/bottom).

Another important setting in ACP/Focusmax with external add-on motors is to ensure the final focus movement is always inwards, the focuser drives out to far firstly and then moves into focus driving inwards only so that backlash is accounted for, I guess there must be something similar in SGP?

Lastly how was the seeing on the night? poor seeing will result in a poor focus and nothing SGP will do can correct for that. The jet stream has been pretty much running over the whole of the UK this last week and seeing down here on the South Coast has been very poor in between the rain bands. Despite the observatory opening to image under ACP control for twenty hours this week it only managed thirty minutes of captures, the rest of the time seeing fell well below the FWHM quality thresholds that I have setup and ACP didn't bother to begin any sequence plans after Tuesday.

William.

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I use a home-built focuser, but usually don't get too many issues, apart from some blustery nights... below are the settings I've come to use, that stops the system re-doing focusing every few images....

1699323702_AFSettings.png.b4042cb703a9db1afbbcb7a20e654bdd.png

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Posted (edited)
1 hour ago, blinky said:

I have been trying for a few weeks now but cant get the autofocus to work properly o SGPro.  Initially I had the first move of the focuser a little flat and was told this was due to backash.  I have now increased it to 250 and last night the VCurves looked bang on, I also never got the error I had had previously where SGPro said the HFR was not as good as expected.   On looking today at an image though Im still not sure its in focus.  Im pretty much out of ideas of what else to change, especially as Im getting a good VCurve.

My setup is a Pegasus focuser, connected to a WO ZS73 which has a R&P focuser.  Hanging off the focuser is a OAG, ZWO Filter wheel and ASI1600.

 

It would be nice if you share your settings.

I use DIY focuser and noticed that Autofocus is not perfect in SGP,

Usually I had bad results while seeing was poor as my default filter exposures did not match the environment... So I made all a bit longer, - just in case (LRGB 10sec Bin2, NB 25sec Bin x2), it looks like now all work good.

Edited by RolandKol

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i had another look and some of the focus runs were OK - Im actually wondering if it was down to seeing or something.

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Just now, blinky said:

i had another look and some of the focus runs were OK - Im actually wondering if it was down to seeing or something.

Most likely seeing...

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Blinky,

I use SGP with a Lakeside focuser and have encountered a range of issues leading to the HFR warning message, most of which I've managed to solve.

  • Seeing variations might be a cause, depending on how long your integrations are and how long your overall autofocus routine is. I used to have SGP set so that the guide-star was re-centered and guiding stabilised in-between each frame; that extended the time taken for the autofocus process, and recently I've just turned off the auto guiding during autofocus, resulting in much quicker AF routines and no issues with resuming tracking. You might avoid issues due to longer timescale variations in seeing by using this approach.
  • Have you checked for any slippage, rotation of the motor etc, that might introduce a slight shift between the position of the focus at the optimum point, and the position which the system returns to at the end of the focus routine? It would be worth comparing the optimum focus settings as a function of time and temperature across several nights. Slippage doesn't have to be large, or noticeable when you look at the hardware during a run. I detected slippage by seeing a systematic shift towards smaller autofocus position settings over the course of several nights, due to a small slip during each AF routine. In my case, each slip in itself wasn't enough to give the HFR error - just a few steps, but clearly there was a small difference between the optimum and achieved focus position at each run of autofocus. 
  • Another issue I've occasionally come up against is due to guiding not being settled during integration of the final AF frame (taken at the optimum location). This leads to a slight elongation of the stars, which skews the HFR. Once settled, the HFR agrees with the value at optimum focus, within the tolerance bounds. I don't see any sign of this in the image you posted, but it's worth keeping an eye. There are a few posts on the SGP forum relating to this issue.

Just some things to investigate if your issues persist.

 

Nigel

 

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250 is a lot of backlash if you ask me. Right time to put the thinking cap on. Check if the coupler is tightened properly, nothing is loose from the stepper motor end and the end which slips in to the focuser. I had the exact same issue not too long ago and it was just that and since then it's been working beautifully.

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250 sounds a lot but is only 3 or 4 mm

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13 hours ago, blinky said:

250 sounds a lot but is only 3 or 4 mm

mm?

Do you know your scope's critical focus range?

my 130PDS has 45 microns :)

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Hi Blinky,

I think your settings are probably OK, but I see that your bin size in <AutoFocus Options> is set at 2 x 2. Check that it is also set at 2 x 2 in the  <Frame & Focus > controller as I believe these must match.  I had odd results until thet did. Also try 2.0 second exposures if seeing is poor.

I am a fairly new adopter of SG Pro autofocus and have since had it running fine under very good sky conditions. Getting <step size> correct is vital for success and a nice V curve and hence best HFR. There is a very good U-tube video that helps with that calculation. I found the SG Pro default was way below where necessary as my focuser has a full range of 65,500 steps. This depends on each individual rig. 

But last time out, when I was largely testing other features and CWPI, I was blighted by a lot of intermittent thick cloud, and eventually, my target dropped below the roof of my house with very few stars then being visible and concentrated in a small area between my chimney and a higher gable (so this wasn't obvious from indoors). I was so focussed on what was happening indoors on my screen I completely missed what was happening outside in real life. It is not the first time I have done something similar in my warm cosy mission control. I am not saying this is your problem, simply that seeing conditions are indeed very material to autofocus success. 

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Yeah on looking again it may well just be bad seeing and I’m paranoid! Just annoying the weather has turned and it’s likely to be ages before I can have another shot at it.

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On 09/03/2019 at 10:15, blinky said:

I have been trying for a few weeks now but cant get the autofocus to work properly o SGPro.  Initially I had the first move of the focuser a little flat and was told this was due to backash.  I have now increased it to 250 and last night the VCurves looked bang on, I also never got the error I had had previously where SGPro said the HFR was not as good as expected.   On looking today at an image though Im still not sure its in focus.  Im pretty much out of ideas of what else to change, especially as Im getting a good VCurve.

My setup is a Pegasus focuser, connected to a WO ZS73 which has a R&P focuser.  Hanging off the focuser is a OAG, ZWO Filter wheel and ASI1600.

image.thumb.png.db25dfc1fe1f632b9742408796763aec.png

Can you post a sample of your v-curve. Also what is your exposure times on your filters during the auto focus.

 

Steve

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Hi Steve,

 

Dont have the V Curve anymore but it looked good - the exposure time was 6 seconds

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