PHD Guiding Basic Use and Troubleshooting

[Owmuchonomy]

Hi Gary, I'm not much of an expert in guiding to be honest, although i do manage it with PHD2 but my guiding pixel scale is 5.15"/px.

[GaryCH]

Thanks for your input, it certainly gives me another line of investigation. I might just have to bide my time and wait until I can afford a more suitable guide scope, or somehow convert my finder scope (I think is 50mm) to be able to take, and focus with, my webcam and/or buy a better guide cam.

I'm completely new to guiding so even the basics still seem quite daunting to me!

Gary.

[IanL]

Sounds very much like there is no star in the image and so PHD will just bes stretching the noise to produce the grainy white out you see. Things to check:

- Focus. Start with the moon as it will be obvious when it is the frame and then get focus.

- Framing. Next try a bright star or planet. You will still get a white or black snowstorm until you have a star in the frame. Bear in mind the guide scope may not be pointing at the same spot as the main one.

- Gain/brightness. Test this on the moon too in order to get in a sensible range for night time use.

- Exposure length. I don't know what the max length is for your webcam so do some testing. Bear in mind that a long exposure in PHD may still only end up in a short one at the camera if the hardware or driver don't support long ones.

[GaryCH]

Thanks Ian, and btw thanks for your original post in this thread. I've read through it a few times and I'm quite certain that I'll be referring back to it to fine tune the settings once I'm up and running!

I take all your points onboard, especially the last one referring to exposure times and drivers for the web cam as i think the guide scope should have had something in the image as I tested the alignment during the day and it looked pretty good. I'll look into it as it's still cloudy so I'm ready when the skies clear and let you know!

Thanks again,

Gary.

[astrodude]

I am fairly new to guiding, but I don't think focal length is an issue. (1) Have you tried taking dark frames to improve your image. (2) Finding the focus point can also be difficult at first. I have tried racking the focuser in and out fully and only got static with a lodestar x2. It turned out that i needed more back focus and had to add an extension to the front of the lodestar. Try your camera at early dusk on a distance terrestrial object that is easier to see such as a tree or building to check the focus point. You will have to play around with exposure, it might need to be 0.1sec or even faster at dusk but it is much easier than trying to find a star when you are not in focus. Good Luck.

[GaryCH]

I used the dark library in phd2, it took the darks and saved them when I first connected my webcam. Hopefully that works ok.

I have no problem focussing on terrestrial object but I've only managed to test it to a range of approximately 1/2 mile (at least) and that left me with the majority of the focuser still to use but I will certainly confirm that when the moon next appears to see if that's enough try to get out at dusk, as you suggest.

Many thanks Astro,

Gary.

[julian489289]

I have an Explore Scientific 102 mm F/7 APO refractor.  I am guiding this using the magnificent mini guide scope package with the Orion starshoot camera and the 9x50 Focal length 162mm guide scope all mounted on my HEQ5 pro mount.

I have used the original PHD without many issues before and achieved smooth guiding graphs but I have recently upgraded to PHD2.  Ever since this time, I am having issues with my guiding.  Most recently the guide cam kept crashing however, however, I reloaded the software and that issue seems resolved now, fingers crossed!

I have read the tutorial, which is very detailed and helpful, thanks.  However, I was trying last night to guide on M66 in Leo and the graph was awful.  I played with the hysteresis & aggression altering both in opposite ways but could not get a smooth guide graph.  So I closed down PHD and tried again to calibrate on a guide star.

Then PHD would not complete the calibration stage.  One main issue that I had last night (and always) is that during calibration of the guide star typically it goes west & east 15-20 steps but north south 30-50 steps.  Why a difference in the two?

Also the guide cross hairs move west say 15 steps but when they move back the same steps east the cross hairs do not centre back on the star they are usually out of the green box that is around the star.  It then does clear backlash sometimes upto 7-10 steps but does not recentre the star in the green box with the cross hairs.  So when the north south calibration starts it is not aligned with the star initially and ends up even further away after doing sometimes upto 50 steps.  It then read final nudge south 1 and the program goes no further.

I took some screen shots to try and explain this issue in pictures.

https://www.dropbox.com/s/i8sxikrzbljnogq/Screenshot%20%2859%29.png?dl=0

https://www.dropbox.com/s/ivsc4y4y4wwjkw4/Screenshot%20%2860%29.png?dl=0

https://www.dropbox.com/s/o7n4r5sn0ohcc1b/Screenshot%20%2861%29.png?dl=0

https://www.dropbox.com/s/px8lv5bhte42h8f/Screenshot%20%2862%29.png?dl=0

https://www.dropbox.com/s/gt56y00vbrc3ia9/Screenshot%20%2863%29.png?dl=0

https://www.dropbox.com/s/h33fnbuz4yw03yd/Screenshot%20%2864%29.png?dl=0

https://www.dropbox.com/s/s2yb83adnbf798f/Screenshot%20%2865%29.png?dl=0

For the mount, I have RA & Dec algorithm set to Hysteresis both set to 10 for hysteresis and aggression 100.  Hys Min move 0.23, Dec min move 0.22 & max duration RA & Dec at 2000.   Dec guide mode is set to auto and I have set the calibration step to 3500 ( i did try the calculate option but his never seemed to work). Typically I chose a guide star with SNR 40-50. 

The camera I set to 1.5 s refresh.

When I used to calibrate in PHD, the cross hairs moved west and then east centreing back onto the star before starting north and south and again finishing back up on the star.  What have I set wrong and why is the program doing this during calibration?  I assume that this maybe the issue with the poor guiding?????

I would appreciate any help in resolving this, please

Kindest regards

Julian

[Xplode]

Firsly you need to check your guide speed. If you use EQMOD with pulseguiding i suggest you set it to 0.5x under "ASCOM pulseguide settings) in eqmod. If you use ST4 you also have an option there to set it to 0.5x. I have tried lower settings, but found calibration to take more time without making guiding more accurate.

I calculated your needed calibribration step to 1850ms.

I also suggest you change dec algorithm to resist switch.

SNR 40-50 seems very high? I usually guide at stars with SNR 7-12

[julian489289]

Thanks Ole.

My pulse guide setting in Eqmod is 0.1 for both RA & Dec, will change to 0.5.

If I calibrate any lower than 2000 steps PHD2 does n't calibrate.  I was initially using dec algorithm at resist switch when I had the issues but changed it to hysteresis after reading some other forum and was to give this a go.  I have n't tried it on hysteresis yet??

I usually use the software to pick the guide star and it seems to go for the higher ones??  Will bear this in mind.

Any idea regards the cross hairs on calibration run?

[Xplode]

Guide speed works together with calibration step so 1850ms should work.

I did the calculations for your setup at 0.1x speed and calibration step would need to be 9200ms! I guess this is why your earlier settings didn't work.

Auto select star should work great, never had a problem with it myself so i suggest you stick to it too.

From what i understand hysteresis on DEC should only be used on mounts without backlash...so none of the Skywatcher mounts and most other cheap mounts won't be suitable either.

[julian489289]

Do you think changing these settings will sort how the cross hairs track the star on calibration ie  returning back to the star before doing north south ?

[julian489289]

Also I have found a version 2.5.0, I will try this as well

[Davey-T]

Thanks for your input, it certainly gives me another line of investigation. I might just have to bide my time and wait until I can afford a more suitable guide scope, or somehow convert my finder scope (I think is 50mm) to be able to take, and focus with, my webcam and/or buy a better guide cam.

I'm completely new to guiding so even the basics still seem quite daunting to me!

Gary.

I've guided fine using 900mm f/l scope, be better off spending on a dedicated guide camera, Loadstar is good but cheaper options available.

Dave

[GaryCH]

I've guided fine using 900mm f/l scope, be better off spending on a dedicated guide camera, Loadstar is good but cheaper options available.

Dave

That's good to know, thanks Dave.

I have had a bit of joy guiding now - my first attempt was very erratic because I forgot to change the speed and it was all over the place but I was pleased to track a star in PhD none the less! My second attempt I adjusted to sidereal and the graph was much better but during my attempt at a ten minute exposure the scope ended up near a street light as Pleiades was so low in the sky and completely washed the image out!

I think my main problem is my combination of a quickcam pro 4000 with the 800mm guide scope which gives me a very small fov - the pixel scale is 1.44 ish - and even when I was looking at Pleiades, I still struggled to find a star. When I tried to slew to other targets I couldn't find any stars again even though I could see them in my finder scope. I think this is a fov and sensitivity of the web cam problem, it just doesn't seem to be able to pick up anything other than very bright stars.

I mount my guide scope on top of the imaging scope with a homemade bracket. I'm very happy with the solidity and lack of flexure but, I have no adjustment on it. My next project (now I know that it does work to a point) is to add some adjustment to the bracket so I can centre the guide scope properly and perhaps offset it to find a bright guide star that would otherwise not be in the fov.

Thanks for all the advice on the matter, I'm up and running but, I still have work to do! I managed to track a random area of the sky for ten minutes yesterday with no trailing so I must be on the right track!!

Gary.

[kalasinman]

Do you think changing these settings will sort how the cross hairs track the star on calibration ie  returning back to the star before doing north south ?

Don't worry about that. When it is calibrated the lines turn green and center on the star again.

[julian489289]

Well I finally got out on a clear night to try out guiding with PHD2. 

With all of your kind help and suggestions, all of the issues that I had before are now sorted, with a guiding rate set at 0.5 this sorted the calibration and gives a great looking graph.  On calibration, set at  1850 with 0.5 set, PHD calibrated itself with only 7 steps in each direction.  Previously it was over 40 steps on some occasions.  10 minute subs with pinpointed stars, PHD is fab!!

Thanks again

[Woodwind]

A really good set of notes IanL.

I meddled with all sorts of software and systems some ten yers ago and then one day went out and bought the Orion Starshhot autoguider. What a difference it made. As you mention, suddenly all the things you thought were going to be nigh on impossible became easy and the stars turned out to be round after all.

After a good mount I would say that an autoguider is the next best thing to invest in if you are going to be imaging. It is a terrific morale booster !!

[Peje]

A really good set of notes IanL.

I meddled with all sorts of software and systems some ten yers ago and then one day went out and bought the Orion Starshhot autoguider. What a difference it made. As you mention, suddenly all the things you thought were going to be nigh on impossible became easy and the stars turned out to be round after all.

After a good mount I would say that an autoguider is the next best thing to invest in if you are going to be imaging. It is a terrific morale booster !!

Interesting, so you add that guider to an upgraded finder scope ( I assume) and it controls the mount directly? Is it simply powered via usb or does the pc have some sort of interaction with the guider

Edited June 18, 2015 by Peje

[alcol620]

Hi  julian489289 what setting on PHD do you use.? Are you Drizzling as well? I wondered what those blips were on you PHD data graph

Alec

[Woodwind]

Interesting, so you add that guider to an upgraded finder scope ( I assume) and it controls the mount directly? Is it simply powered via usb or does the pc have some sort of interaction with the guider

You have a second small (60mm approx) scope piggy-backed and as long as it points in roughly the same direction, and also as long as the mount is roughly aligned to the Pole Star, you simply select a single star to guide on and press the button. The link goes direct to the mount at that point and you have no further interraction for the guidance to take over.

You do have to select a star and that requires you to have a PC or laptop for the display of course. But that really is about the sum total involvement at a basic level. If you want to get more involved you can select a number of parameters such as refresh rate and guidance tolerances etc.

It is pretty close to a "plug and play" guidance system as far as I am concerned.

[Peje]

You have a second small (60mm approx) scope piggy-backed and as long as it points in roughly the same direction, and also as long as the mount is roughly aligned to the Pole Star, you simply select a single star to guide on and press the button. The link goes direct to the mount at that point and you have no further interraction for the guidance to take over.

You do have to select a star and that requires you to have a PC or laptop for the display of course. But that really is about the sum total involvement at a basic level. If you want to get more involved you can select a number of parameters such as refresh rate and guidance tolerances etc.

It is pretty close to a "plug and play" guidance system as far as I am concerned.

That sounds brilliant. I had planned to use an ST80 as the guide scope but that's still a while off yet

[Woodwind]

That sounds brilliant. I had planned to use an ST80 as the guide scope but that's still a while off yet

You asked about power supply - that is usually provided by one of the two cables that connect the guide camera to the PC or to the mount (the former can be one of several types of USB, the latter a standard US phone-type connector); I am not sure which one does the power, to be honest. Some guide cameras might use separate power supplies but the Orion Starshoot system is the one I use and it is as described with only the two cables.

[julian489289]

Hi  julian489289 what setting on PHD do you use.? Are you Drizzling as well? I wondered what those blips were on you PHD data graph

Alec

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Celestron 8SE, Skywatcher Evostar 80ED DS-Pro, ASI120MC, Canon 1100D & 550D modded, AZ EQ6-GT

Hi Alec,  I dither between subs and I have found that you must increase the pause between exposures sufficiently enough to allow PHD to settle down after each dither.  I do also drizzle 2x in the stacking parameters.  The blips are a graph setting which show when a correction has been made by PHD.

Julian

[alcol620]

Hi Julian

Thanks for feedback

Regards

Alec

[bendavidson]

What a brilliant beginner's guide - thank you so much Ian.

A couple of questions re the pixel scale calculations.  I have a Canon EOS 700d, similar to the one you used as an example here.  Your EOS 500d has 15.5 megapixels (15.1 effective megapixels) and a chip size of 22.3 x 14.9mm.  That's a chip size of 22,300µm x 14,900µm = 332,270,000µm2, divided by 15,500,000 pixels, comes to 21.44µm2 per pixel (or 22µm2 per pixel if you're only counting the effective ones).  Yet you say the chip's pixels are 4.7µm2. 

1/ Your number looks like the square root of mine.  Is that right and, if so, why?

2/ Also if so, how come you are using the effective number of pixels rather than the total number?

Thanks in anticipation.

Ben