PHD question

[starpusher]

I was looking at the website question and answer tutorial [http://www.stark-labs.com/wiki/doku.php?id=tutorials:phd:faq#setups_settings]

The problem I have with PHD is this:

“Q. After a fine calibration, the star just works its way “up” out of the cross hairs.”

And one answer is:

“6. If your using the Autoguide port.. Make sure to check the autoguide settings for BOTH RA and Dec. 50% to 99%.”.

Can anyone please explain what these percentages are?

Regards,

Richard

[adamsp123]

The % is the amount of agression in the signal as I understand it, I would leave it at 80-90% and fiddle with other settings. I had a similar problem and in my case it was an imbalance in the DEC axis.

[starpusher]

Thanks Pete,

It's the empahasis on the word BOTH that puzzles me. I thought the PHD agression adjustment, after clicking the brain icon, only applied to RA and not DEC. I have checked my balance and that seems good but there is a tiny amount of play in the DEC axis. I might have a fiddle and try to remove that play on the mount.

Regards,

Richard

[Tim]

It depends

Are you using the ST4 autoguider port on the mount? As I understand it, you want to reduce the speed of those so that the autoguiding can make several fine adjustments rather than overshoot the thing. Typical settings for the ST4 port might be RA 50% and DEC 25%.

If you are not using the ST4 port, eg, pulse guiding through EQDIR, those settings mean nothing.

Actually, although only slightly related, the EQMOD autoguiding PDF file will probably have the accurate answer, I have it printed at home, but am at work atm, you can find it online though.

[starpusher]

Tj,

I am connected to the autoguider port (I think it is referred to as ST4) on the mount (HEQ5 with Synscan upgrade) and the cable then connects to the QHY5 guide camera on the guidescope. But I don't know how to check the settings for the port i.e. RA 50% and DEC 25%, I don't even know what they are! I guess these %'s are not those associated with aggressiveness in PHD?

Regards,

Richard

[Tim]

Richard, they will likely be in your synscan unit if you are using that as your goto? IIRC there is only one setting though, and it will be 'autoguide rate' or something similar.

In eqmod you can set each axis seperately.

Are you having problems then? Its more likely related to your polar alignment than settings in PHD. Try and get your alignment good enough so that it will track a star and hold it fairly central for 10 mins or so without drifting, without PHD guiding it. If PHD has to fight alignment drift too much it will always struggle.

[starpusher]

TJ,

There is an "Auto Guide Speed" -1x,0.75x,0.5x,0.25x,0.125x.

I will have to recheck but I think it is set at 1x.

There is also a Tracking Rate - Sidereal, lunar, solar, PEC+ Sidereal, Stop Tracking. I will confirm but I think it is set at Sidereal.

I have never tried eqmod.

I find that the guide star drifts from under the cross hairs after say 2 minutes of PHD guiding. It works a little better if I increase the RA aggressive to the max 120% and hysteresis increased to 35% but the star still drifts away after about 3 or 4 minutes.

I have ordered a reticule eyepiece so I can hopefully get a good drift alignment and then check out the mount using PEC+ Sidereal.

Thanks for your help.

Regards,

Richard

[adamsp123]

What setting do you have for the pulse time in RA and DEC? this sets the number of pulses you need for calibration, I set mine to get between 10-15 in W-E cal and N-S if you are calibrating and need a lot more pulses to calibrate then I would suggest you increase the guiding pulse width settings.

Make sure you have good polar alignment as well if it is too far off PHD won't cope with the rapid change of guidestar positon.

BTW what scope are you using for the guider.

[starpusher]

Pete,

I get about 15-20 calibration steps for both W-E and N-S. Backlash only 2-5 steps.

I will look at the polar aligment more closely.

The guider is a refractor 80mm, f600mm.

The imaging scope is a reflector 200mm, f1000mm

Regards,

Richard

[Beyond_Vision]

What setting do you have for the pulse time in RA and DEC? this sets the number of pulses you need for calibration, I set mine to get between 10-15 in W-E cal and N-S if you are calibrating and need a lot more pulses to calibrate then I would suggest you increase the guiding pulse width settings.

Make sure you have good polar alignment as well if it is too far off PHD won't cope with the rapid change of guidestar positon.

BTW what scope are you using for the guider.

Pete,

Richard isn't using pulse guiding he is guiding using a QHY5 with a guider port connected to the mounts ST4 port. It sounds like PHD is managing to calibrate so calibration time shouldn't be the cause of the problem. It would be worth doing the drift alignment to ensure you have reasonable alignment then see how you get on. PHD usually works well with the default settings and only needs the calibration time to be tweaked when using short focal length guide scopes.

Regards

Kevin

Regards

Kevin

[adamsp123]

Kevin,

what I should have said was "calibration step" but as the number of steps Richard was getting in calibration seems fine no need to alter, I agree the default settings normally work well, I use a finderguider so the calibration step I use is between 1500 and 2000ms dependeing on which part of the sky I am looking at, near the pole I need longer steps.

I have found pretty good polar alignment is needed as is getting the balance right and cables neatly tied down and not flopping around.

[starpusher]

Thanks for your help. I will let you know how I get on

[Tridge1]

I have had many frustrating nights with PHD using the standard Orion packaged 80mm guide scope, starshoot autoguider, mounted piggy back on an Orion EON 80mm ED, mounted on a Skyview Pro EQ with Synscan goto, with autoguider port. Not as easy as some folks seem to have. The software seam very sensitive and I have a little trial and error each time to get it working. My set up works best shooting to the east and last night after 6 previous outings I got it tracking reasonably well shooting to the west.

Level mount accurately, align accurately on Polaris, I use a polar scope. Make sure my guider chip axis is perpendicular to the RA. Make sure I have scope weight slightly off balance to keep the RA motor loaded. I marked my weight shaft so when I guide shooting west, I can change the weight position to keep the RA motor loaded. I have succesfully done this without having to do a new start alignment procedure. I usually just do a one star alignment in the beginning (lazy) and get good results using the goto system. After all this and focusing the guide camer to get reasonably sharp guide stars.

I am direct cabled from the guide camera to the mount guide port.

Must set Synscan to 1.0x guide speed

Start with RA agressivenes at 100, but to the west usually 120

Leave Hysterisis at 10

I leave Dec tracking off as my drift is along the RA axis

Calibration step starting at 800, sometimes as high as 900

Use subframes

Exposure setting 1.5 or 2.0 s

I usually have to play around with RA, Calibration, and Exposure time to get it tracking. My next efforts are going to be to check voltage levels between all components to see I am getting good voltage signals to and between the guide camera and the autoguider port. I have no trouble connecting my scope to my PC planetarium software and finding any object I want. Just can't seem to get my autoguiding package working consistently without the above. I may try the Shoestring USB guideport adaptor to see if it makes any difference in control stability.

Anyway, this is my saga.

Richard W

[adamsp123]

Richard, how many steps does it take your setup to calibrate both in RA and DEC?

[Tim]

Welcome to SGL Richard. I'm not certain what your exact problem is really? One thing though, usually the guide speed in the sysnscan is set to less than 1.0, probably 0.5 or 0.25, but im not sure how or if that will affect your setup in particular.

[starpusher]

Richard (W) maybe it’s because we have the same first name but your difficulties sound at little bit like mine.

I recently received my reticle eyepiece and checked the polar alignment using first a south and an east star and found that there was hardly any north south drift suggesting the alignment is probably good enough. But I did notice drift in RA. The magnification was 160 and the RA drift was significant after only a couple of minutes. In fact it seemed like to look like what I see on the PHD screen when it is guiding i.e. a one sided increment drift after about 2-3 minutes that sort of just stays there and then very slowly worsens up to about 6 minutes. I have tried all of the usual adjustments for PHD, aggressiveness, hysteresis, exposure time e.g 70% - 120%, 15% to 35%, 0.5 to 2.0 seconds. The calibration is fine (18- 30 stepsand I get the “guiding” message. It seems my best settings are RA aggr = 100 – 110 %, hyteresis = 25- 30 %, exp = 0.5 – 1.0 sec. My supply voltage is good, measures about 13 volts. I have tried different guides speeds and it seems that 0.5 works the best. Even at its best the image at say a 4 minute exposure shows star trailing and the stars look like doubles a bit little dumbells all aligned in the same direction (probably RA but have not confirmed). I have tried different guide stars and get the same dumbbell stars. I did some images of M51 last night and for one of them I tried without PHD and only used the mount tracking. This image was very similar to the guided images certainly no worse, lots of little dumbbells. It occurred to me that my HEQ5 might have free play in the RA axis and I did try to feel this by moving the scope and balance weights and I thought I could feel a little bit of play. One thing I didn’t do was have the PEC switched on (I forgot even though I did the training!!). So perhaps I should try to reduce the RA free play or at least try the PEC. Does anyone have any other ideas… thanks for your thoughts so far?

Regards,

Richard

[adamsp123]

I have come to realise is the cable routing/strain relief is critical on my set up, any strain seems to make the system a "twang" ie I see in my case the DEC graph especially "bounce" around and I get elongated or double stars.

Choice of guide star seems to matter, if I see the guidebox jumping around during guiding I try another star and some seem to work much better, I think PHD sometimes has trouble knowing where the guide star centre is located - note brightness is not a factor IMO.

I also seem to get better results when I have the step time quite long, OK I use a finder guider but I have increased the step length such that it takes 10 or less steps to calibrate. Now when I start the run the PHD graph is quite bouncy but after 5 mins it settles down very nicely and BTW I leave hysteresis at 10, more and I believe it will likely degrade the guiding, lower hysteresis will take longer for the guiding to settle but it should be smoother.

My 2pence worth

Pete

[NickH]

It may be worth (moderators?) setting up a PHD settings/equipment list, like a table with scope/mount (side by side, or piggyback etc)/camera/settings in PHD list, plus any quirks in balance... given that so many of us use this?

[starpusher]

Pete,

I don't think it is cables pulling or something similar to that mainly because I could see the star wander out of the recticle centre in the RA direction as the mount tracked it. This was only after a few minutes when I was looking through the eyepiece i.e. no camera, cables attached, just telescope, mount and eyepiece (and my eye). The guidescope was still piggy backed but nothing connected to it. This is what makes me think it is something to do with free play or some other mechanical quirk in the mount's RA axis.

Good idea Nick I will do that!

Regards,

Richard

[adamsp123]

Starpusher, try resetting the PHD settings back to default, after noting your setup, then increase the calibration step time until it takes about 8 steps in RA/DEC for calibration and see how that goes. My reason is you say you calibrate in 18-30 steps and I am wondering if PHD just can't keep up with the star drift you are getting with such small steps.

As I said in my earlier post I now use a setting that calibrates in fewer steps than I used to use, that combined with better cable "management" I seem to be getting better results with PHD.

[starpusher]

Pete,

I had another go last night. This time I couldn’t find a guide star near M51. So I slewed it to Mizar and picked a bright star in that area. The cross hairs on PHD seemed to hold it better. It was a brighter star than I have chosen before. Fiddled with the settings and ended up with RA agg = 100% Hysteresis = 15% (I think these are the default settings). I also had the exposure time quite low = 0.5 seconds. I had set the calibration step to 600 ms (previously 350 / 400) and it was calibrating in say 13 steps (I had not read your post prior to this). So for a four minute exposure the star trailing was still there but improved (more of an egg shape and the stars were not exactly pin-point). The cross hairs certainly held better on the brighter guide star. I noticed the cross hairs drifted off the star’s centre to its edge, and after 30 seconds or a minute tended to move back on to the centre but probably not quite to centre. There was also a bit of wander around the star centre but it at least the cross hairs didn’t leave the star even after about 5 minutes. Maybe I need to use brighter stars in the future. My guide scope is 80 mm, F600mm, should I be thinking about using a shorter focal length and wider field of view to give a better chance of picking up brighter stars? I can adjust the axis of the guide scope relative to the image scope because the its mount rings each have three long screws securing the tube.

Regards,

Richard

[Psychobilly]

If theres no cloud around i always use fainter stars for guiding and adjust the exposure whilst keeping an eye onthe star profile .. you dont want to saturate the guide star...

If theres cloud about i will pick a brighter star to be able to guide through it... its quite suprising how thick the cloud has to be before a decent guidecam loses the star...

It can also help to slightly defocus the guide scope...

Peter..

[starpusher]

Hi Peter,

I had a go last night and found a guide star and it seemed to guide better than I have had in the past for about a five/six minute exposure of M51. I still got the star trails but improved with the the telescope balance weights slightly biased on the east side. Although I could still see the cross hairs wander off slightly after about four minutes and then it pulled the star back. I read somewhere that this can improve the guiding. I think it takes the slack out of the RA and gives the motor something to work against. I know it's not a very good effort but I am getting better at this very very slowly:icon_confused:

Regards,

Richard

[Glider]

Hi StarPusher. I've just read this whole thread and note 2 things right at the top, you had a go at adjusting some play in the DEC mechanism and the mount is a Synscan 'upgrade'.

Reading between the lines I think a common element through the thread seems to be that whatever you do the mount simply isn't moving quick enough to keep up with the star you are guiding on. Thinking laterally, could the mount gearing be wrong?

There was a very long running thread on SGL which eventually found the wrong pair of gears had been engaged when someone has rebuilt their mount.

Just a wild thought.

[starpusher]

Glider,

Thanks, it may be that. Although it seems to hold the star pretty well for about 3 minutes (a minute or two longer with a bit of "tuning" ) and then it tends to drift off. If it were the gears then I would expect it to drift off at the start of the guiding. On the other hand the system might be fighting it... I'll recap on the upgrade instructions.

Regards,

Richard