PHD2 guiding tips

[gregbradley]

I have been using PHD2 guiding on and off. Its a fabulous program and gives superior guiding. Its free and its sophisticated.

The guiding assistant works out the best parameters for your guiding for that night which is a great tool.

The only issue I have had it can lose a guide star and then it does not seem to try to continue and stops if that occurs and does not re-engage the star once the cloud passes like say CCDsoft will (it just simply keeps going until told to stop).

One solution I used now is 1) use really long guide exposures - 10 seconds or more. 2) I fitted a .6X reducer on the end of my SBIG STi guider and these 2 actions makes for a really high signal to noise ratio guide star usually.

But if it were slightly cloudy I would revert to using Sky X for autogudiing which is the same as CCDsofts.

I was getting .62 arc sec guiding last night for quite a while and then it went to .78. That graph was very flat and is the best guiding I have ever seen (AP1600GTO).

Greg.

[RobC]

Greg - (1) I am a bit curious to know how you determined you were getting 0.62 arc second guiding and (2) do you think that long exposure guiding is stopping the guide software from oscillating ?

Cheers

Rob

[PRejto]

Greg,

I can give you a script that will address the very issue you are complaining about! It's just a bit fiddly to run, but it works as advertised and has adjustable parameters such as how long to wait before reestablishing the guide star, etc. You need to run it from a command prompt and you need to install a program to run .pl. I will attach the files a bit later with complete instructions.

Peter

PS Do hyou not find it odd that PHD2 currently won't bin guide cameras? I think that is about to change but at the moment I find the program not sensitive enough for dim guide stars. I also wish the track box size were 2x bigger. It's currently 15x15. TSX defaults to 32x32.

Greg, can you please explain to me exactly what/how CCDSoft tries to reestablish a lost guide star? I have not used the program for guiding for some time now. Thanks!

[PRejto]

Greg,

Attached is the script and a pretty self explanatory help file.

I installed this program (free and just runs in the background after installing):

http://strawberryperl.com

Open your command prompt (make a shortcut!) and see where the default folder is. That is where you place the script file. Then just type in restart_guiding.pl

If PHD2 is running everything from that point is automatic. You can view what restart_guiding is doing in the command prompt window.

For me it works great!

Peter

[codemonkey]

If your camera has an ASCOM driver that allows binning you may be able to use that. I do that now with my QHY5L-II. Unfortunately it resets the pixel size every time, so I need to up it from 3.75um to 7.5 every time I reconnect the camera.

[peter_4059]

Greg,

Have you tried setting Star Mass Tolerance to 100? Setting this to 100 disables the star mass tolerance feature. You also have control over the tracking box size and can increase this to larger than 15x15 however the risk is you end up with multiple stars in the box and this can impact centroid determination. Using darks also helps with guide star S/N if you aren't already doing so.

"'Search region' - specifies the size of the "tracking rectangle", in units of pixels. You may need to increase this value if your mount does not perform well or, more commonly, if it's not well-aligned on the celestial pole.
'Star mass change detection' - tells PHD2 to monitor the brightness and size of the guide star compared to the sky background.
'Star mass tolerance' - if 'star mass change detection' is checked, PHD2 will trigger a 'lost star' error if the measured brightness and size vary by more than this percentage. This might be useful if you have two stars inside the tracking rectangle and you want to be sure that PHD2 doesn't mistakenly switch stars. It can also prevent errors caused by thin clouds, high camera noise, or alpha particle "hits"; but it may be unreliable if you are guiding on a faint star. If you are getting too many 'lost star' errors when the star is plainly visible on the display, try increasing the value of this setting. Setting the value to 100 effectively disables the warnings entirely."

http://openphdguiding.org/man-dev/Advanced_settings.htm#Guiding_Tab

I'm a bit surprised you are having issues with this - what system are you guiding with?

Cheers,

Peter

[gregbradley]

On PHD2 it has several display options. One is a very good graph showing RA and Dec errors plus the correction commands to the mount, the other is a stats board which shows the current average PE error (that 's the .62 I was referring to).

I used the guide assistant which determines guide exposure length and min/max moves. It actually recommended 14 seconds. The AP1600 PE is super smooth so if PA is very accurate (which mine is) then that gives the really super low PE number of .62 arc seconds.

Long guide exposure is basically saying the mounts PE is really good and only needs a minor correction every now and then.

Greg.

[gregbradley]

I can give you a script that will address the very issue you are complaining about! It's just a bit fiddly to run, but it works as advertised and has adjustable parameters such as how long to wait before reestablishing the guide star, etc. You need to run it from a command prompt and you need to install a program to run .pl. I will attach the files a bit later with complete instructions.

Peter

PS Do hyou not find it odd that PHD2 currently won't bin guide cameras? I think that is about to change but at the moment I find the program not sensitive enough for dim guide stars. I also wish the track box size were 2x bigger. It's currently 15x15. TSX defaults to 32x32.



Thanks Peter. You're a gem!

Greg.

[gregbradley]

Thanks Peter.

I'll try that out. I'm not having issues with it in clear skies only when there is a bit of light cloud around where if it gets a cloud it stops.

I'll try that. But that is the problem and not sure if that setting is designed to handle that, perhaps it is. I have not seen anything like that in any other program.

Long exposures and the reducer make for a high SNR and using PHD2 when its fully clear and using Sky X when its perhaps a bit dodgy is what is reliable at the moment. PHD2 seems to do the best job of autoguiding of anything I have used so far.

My system is AP RHA 305 on an AP1600GTO mount, Sky X, AP Ascom driver, PHD2, SBIG STi guide camera in an Astrodon MMOAG and either a FLI Proline 16803 or an SX Trius 694 fitted to FLI 7 position filter wheel with 50mm square filters.

At first I did not like using the reducer with the RHA as the edge stars looked pretty whacky but last night they seem perfectly round and bright.

Greg.

[niharika]

Good to see you are getting comfortable with the mount Greg :)

[peter_4059]

Greg,

Thin clouds will trigger the star mass tolerance error and can cause phd to stop guiding. If you want it to try to keep guiding increase the tolerance to 100.

The other thing to check is the reported guide star S/N. I think you are looking for a number greater than 6 ideally.

[gregbradley]

Yes I am. The tracking is amazing. Best I have seen and that includes a PMX and PME, a Tak, MI250, Vixen Sphinx (well that wouldn't be hard!).

Greg.

[gregbradley]

I will try that. Thanks. A smallish thick cloud that totally blocks the stars is the scenario we need to overcome. I'll set that to 100 but I suspect it will still fail in that situation but hopefully it works. Its a superb program and if its just a setting to handle that then that's even better. But if you commit to a several hour imaging run and you sleep and find out the next day a small cloud stopped the session 30 minutes after you walked away its not a good feeling! (actually happened). SkyX is more reliable that way.

Thanks Peter. I think 6 is the SNR target for calibration but yes it needs to be as high as possible. The reducer and long exposures are giving much higher SNR, more like 40-50.

Greg.

[PRejto]

Greg,

The script I gave you will do exactly what you want. It will recover from a thick and long cloud. It will even find a new star and start guiding if you slew the mount to a new position!

Can you please tell me what CCDSoft does when the guide star is lost?

Thanks!

Peter

[gregbradley]

It keeps imaging with the guide cam. When the cloud clears if your guide star is still in the guide box you used it will reacquire and continue autoguiding.

Greg.

[PRejto]

OK, thanks! That isn't comprehensive enough to do what I need it to do which is to automatically take a full frame view, reselect a guide star and initiate guiding. The PHD2 script does that.

Peter

[troypiggo]

That's exactly what PHD2 does if you follow Peter's advice above ;)

[gregbradley]

Ok thanks Troy. I have set my star mass setting to 100. I'll wait to see how it goes in the next slightly cloudy night. I thought it might be a setting somewhere.

Greg.

[allan gould]

I had this problem with thin cloud at Astrofest where PhD2 would start its "bonging" as thin cloud went past due to a lowering of the "star mass".
I did as Peter has suggested here and increased the setting to 100. No problems and when it lost the star due to cloud it just picked up again when the star re-appeared. Polar alignment with PhD2 is recommended for this to work well - I was doing 30 min subs again.
Allan

[gregbradley]

Thanks Allan.

That's good to confirm that it does that. So that was my only concern with it. Its a super program and is giving me superior guiding to Sky X.

Anyone using the free dither plug in? Not sure how that works. It would need to work with the camera wouldn't it? Otherwise it might to try to dither in the middle of an exposure.

Greg.

[troypiggo]

I agree - dithering should be done from the imaging software between exposures. SGP and Maxim certainly work this way.

[LewisM]

Not sure how different my PHD2 is or what settings I use that differ to others, but I find PHD2 snaps to the guidestar I chose even after stopping guiding for a while.

Anyway...

[lazjen]

You've probably got auto-star selection on and it's grabbing the star again?

I seem to recall that happening for me.

Also, as already mentioned - do the dithering from the imaging software as it will handle it between subs.

[LewisM]

Probably Chris. I know it JUST WORKS,so I don't fiddle :)