PHD2 Guiding Question

[Starwiz]

On 10/08/2020 at 17:56, michael8554 said:

I've looked at the Star Lost positions in the Log and to be honest I don't know what is really happening.
So I will theorise 😆

First you haven't made any Dark or Defect maps for the camera, so the chances of locking on a hot pixel are high.

 

 

PHD2 then continously send Max Dur corrections (up to the horizontal red dotted line), trying to move that pixel into the centre of the guide box, which it never will be able to do.

(Note the vertical scale is 50arcsecs, so the normal guide pulses leading up to the Star Lost are too small to see, and I've only shown Dec for simplicity).

I notice that all the way through your guiding, PHD2 is showing the SAT message on every guide exposure - PHD2 auto select shouldn't select a Saturated star ?

Even on the very low star signal (yellow line), SAT was indicated.

Was the red SAT message not showing on the bottom taskbar?

You might try changing your Star Detection method.

 

Your guide HFD is about 3.5 pixels, so you could deselect Star Mass Detection and set HFD to 2, which is a higher figure than a hot pixel.

Though the PHD2 developers deny it, I believe it is all too easy to widely loose position during a Star Lost situation.

Finally, I think you're very brave leaving your mount unattended for long periods, when the chances of mount Runaway or uncorrected Star Loss are not zero, leading to wrapped cables or tripod/counterweight intimacy .

(and lots of wasted exposures).

Michael

I'm pleased to report I've now had three straight nights of full imaging since I implemented the above changes although it's been completely free of clouds each night.

The last two nights, I've selected the star manually as it always seems to auto-select the brightest star which results in the star being saturated .  Is there a way to change the settings to improve auto-select of the star?

Thanks

John

[alacant]

3 hours ago, Starwiz said:

three straight nights of full imaging

That's great news.

I think we're at about the same latitude. What i find at this time of year in particular is that the seeing -and so the guiding- is dictated very much by the air stream. The coastal strip here north of Alicante is only about 10km wide with steep slopes immediately to our west. Anything with an easterly component throws up haze as the damp air rises and cools. Everything else is dry and so the seeing remains constant all night. I wonder if you may be similarly affected? Maybe worth investigating, particularly as you become more automated. I think guiding is very much affected by seeing.

Cheers 

[Starwiz]

24 minutes ago, alacant said:

That's great news.

I think we're at about the same latitude. What i find at this time of year in particular is that the seeing -and so the guiding- is dictated very much by the air stream. The coastal strip here north of Alicante is only about 10km wide with steep slopes immediately to our west. Anything with an easterly component throws up haze as the damp air rises and cools. Everything else is dry and so the seeing remains constant all night. I wonder if you may be similarly affected? Maybe worth investigating, particularly as you become more automated. I think guiding is very much affected by seeing.

Cheers 

Thanks, that's interesting.  I'm about 3 degrees further south, but it's worth investigating.  Being surrounded by sea, it can get very humid in Malta and I always put a towel over my laptop at night, sometimes finding it quite damp by the morning.  I could also probably do with a better guide camera as the ASI120mc isn't the best choice, especially with OAG.  I originally bought it for planetary use before I even considered imaging DSOs.

John

[alacant]

23 hours ago, Starwiz said:

damp by the morning

Not so damp here until later on in the year, but here's an example with HFD.

Same telescope and guide calibration on consecutive nights. One with easterlies, 3.0, The next, northerlies, 2.6. Same part of the sky:

And here's an example where the air changes direction from East, via south west (along the coastal strip) to north-west (from the altiplano). The relative humidity is in light green. Looks like with a bit of luck, we'll make it through the whole of astro-darkness:)

 

Edited August 15, 2020 by alacant

[Starwiz]

2 hours ago, alacant said:

Not so damp here until later on in the year, but here's an example with HFD.

Same telescope and guide calibration on consecutive nights. One with easterlies, 3.0, The next, northerlies, 2.6. Same part of the sky:

Thanks, that's interesting.

John